A2 Extended Writing Practice
367 minutes
331 marks
Q1.
(a) A spring, which hangs from a fixed support, extends by 40 mm when a mass of
0.25 kg is suspended from it.
(i)
Calculate the spring constant of the spring.
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(ii)
An additional mass of 0.44 kg is then placed on the spring and the system is set into
vertical oscillation. Show that the oscillation frequency is 1.5 Hz.
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(4)
(b)
With both masses still in place, the spring is now suspended from a horizontal support rod
that can be made to oscillate vertically, as shown in the diagram below, with amplitude
30 mm at several different frequencies.
The response of the masses suspended from the spring to the vertical oscillations of the
support rod varies with frequency. Describe and explain, as fully as you can, the motion of
the masses when the support rod oscillates at a frequency of (i) 0.2 Hz, (ii) 1.5 Hz and (iii)
10 Hz.
The quality of your written answer will be assessed in this question.
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(6)
(Total 10 marks)
Q2.
Deep space probes often carry modules which may be ejected from them by an explosion.
A space probe of total mass 500 kg is travelling in a straight line through free space at 160 m s–
1
when it ejects a capsule of mass 150 kg explosively, releasing energy. Immediately after the
explosion the probe, now of mass 350 kg, continues to travel in the original straight line but
travels at 240 m s–1, as shown in the figure below.
(a)
Discuss how the principles of conservation of momentum and conservation of energy
apply in this instance.
The quality of your written communication will be assessed in this question.
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(6)
(b)
(i)
Calculate the magnitude of the velocity of the capsule immediately after the
explosion and state its direction of movement.
magnitude of velocity = ....................................... m s–1
direction of movement ............................................................
(3)
(ii)
Determine the total amount of energy given to the probe and capsule by the
explosion.
answer = ....................................... J
(4)
(Total 13 marks)
Q3.
A student was required to design an experiment to measure the acceleration of a heavy
cylinder as it rolled down an inclined slope of constant gradient. He suggested an arrangement
that would make use of a capacitor-resistor discharge circuit to measure the time taken for the
cylinder to travel between two points on the slope. The principle of this arrangement is shown in
the figure below.
S1 and S2 are two switches that would be opened in turn by plungers as the cylinder passed over
them. Once opened, the switches would remain open. The cylinder would be released from rest
as it opened S1. The pd across the capacitator would be measured by the voltmeter.
(a)
Describe the procedure the student should follow, including the measurements he should
make, when using this arrangement. Explain how he should use the measurements taken
to calculate the acceleration of the cylinder down the slope.
The quality of your written communication will be assessed in this question.
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(b)
When the student set up his experiment using the arrangement shown in the figure above,
he used a 22 μF capacitor, C, and a 200 kΩ resistor, R. In one of his results, the initial pd
was 12.0 V and the final pd was 5.8 V. The distance between the plungers was 2.5 m.
(i)
From the student’s result, calculate the time taken for the cylinder to reach the
second plunger.
answer = ................................... s
(3)
(ii)
What value does this result give for the acceleration of the cylinder down the slope,
assuming the acceleration is constant?
answer = ............................m s–2
(2)
(Total 11 marks)
Q4.
(a) Long cables are used to send electrical power from a supply point to a factory some
distance away, as shown in Figure 1. An input power of 500 kW at 25 kV is supplied to
the cables.
Figure 1
(i)
Calculate the current in the cables.
answer = .................................A
(1)
(ii)
The total resistance of the cables is 30Ω. Calculate the power supplied to the
factoryby the cables.
answer = ...............................kW
(2)
(iii)
Calculate the efficiency with which power is transmitted by the cables from the input
at the supply point to the factory.
answer = ................................%
(1)
(b)
In Great Britain, the electrical generators at power stations provide an output at 25 kV. Most
homes, offices and shops are supplied with electricity at 230 V. Power is transmitted from the
power stations to the consumers by the grid system, the main principles of which are shown
in Figure 2. In this network, T1, T2, T3, etc, are transformers.
Figure 2
(i)
Explain how a step-down transformer differs in construction from a step-up transformer.
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(1)
(ii)
Explain why the secondary windings of a step-down transformer should be made
from thicker copper wire than the primary windings.
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(2)
(c)
Discuss the principles involved in high voltage transmission systems, explaining why a.c.
is used in preference to d.c. and how the energy losses are minimised.
The quality of your written communication will be assessed in this question.
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(Total 13 marks)
Q5.
(a) A transformer operating on a 230 V mains supply provides a 12 V output. There are
1150 turns on the primary coil.
(i)
Calculate the number of turns on the secondary coil.
answer = ........................... turns
(1)
(ii)
A number of identical lamps rated at 12 V, 24 W are connected in parallel across the
secondary coil. The primary circuit of the transformer includes a 630 mA
fuse.Calculate the maximum number of lamps that can be supplied by the
transformer if its efficiency is 85%.
answer = .......................... lamps
(2)
(iii)
The transformer circuit includes a fuse. Explain why this is necessary.
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(1)
(iv)
Why is the fuse placed in the primary circuit rather than in the secondary circuit?
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(1)
(b)
The figure below shows an experimental arrangement that can be used to demonstrate
magnetic levitation. The iron rod is fixed vertically inside a large coil of wire. When the
alternating current supply to the coil is switched on, the aluminium ring moves up the rod
until it reaches a stable position ‘floating’ above the coil.
(i)
By reference to the laws of electromagnetic induction explain
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why a current will be induced in the ring,
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why the ring experiences a force that moves it upwards,
•
why the ring reaches a stable position.
The quality of your written communication will be assessed in your answer.
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(6)
(ii)
What would happen to the ring if the alternating current in the coil was increased
without changing the frequency? Explain your answer.
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(2)
(Total 13 marks)
Q6.
(a)
Define the gravitational potential at a point in a gravitational field.
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(2)
(b)
The figure below, which is not drawn to scale, shows the region between the Earth (E)
and the Moon (M).
(i)
The gravitational potential at the Earth’s surface is –62.6 MJ kg–1. Point X shown in
the figure above is on the line of centres between the Earth and the Moon. At X the
resultant gravitational field is zero, and the gravitational potential is –1.3 MJ kg–1.
Calculate the minimum amount of energy that would be required to move a Moon
probe of mass 1.2 × 104 kg from the surface of the Earth to point X. Express your
answer to an appropriate number of significant figures.
answer = .................................. J
(3)
(ii)
Explain why, once the probe is beyond X, no further energy would have to be
supplied in order for it to reach the surface of the Moon.
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(1)
(iii)
In the vicinity of the Earth’s orbit the gravitational potential due to the Sun’s mass is
–885 MJ kg–1. With reference to the variation in gravitational potential with distance,
explain why the gravitational potential due to the Sun’s mass need not be
considered when carrying out the calculation in part (b)(i).
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(2)
(c)
The amount of energy required to move a manned spacecraft from the Earth to the Moon
is much greater than that required to return it to the Earth. By reference to the forces
involved, to gravitational field strength and gravitational potential, and to the point X,
explain why this is so.
The quality of your written communication will be assessed in your answer.
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(6)
(Total 14 marks)
Q7.The diagram below shows the orbits of two Earth satellites, a communications satellite in a
geosynchronous orbit and a monitoring satellite in a low orbit that passes over the poles.
(a)
The time period, T, of any satellite in a circular orbit around a planet is proportional to r3/2,
where r is the radius of its orbit measured from the centre of the planet. For a satellite in a
low orbit that passes over the poles of the Earth, T is 105 minutes when r is 7370 km.
(i)
Calculate the height above the surface of the Earth, in km, of a satellite in a
geosynchronous circular orbit.Give your answer to an appropriate number of
significant figures.
height above surface .............................. km
(4)
(ii)
Calculate the centripetal force acting on the polar orbiting satellite if its mass is
650 kg.
centripetal force ................................ N
(2)
(b)
These geosynchronous and polar satellites have different applications because of their
different orbits in relation to the rotation of the Earth.
Compare the principal features of the geosynchronous and polar orbits and explain the
consequences for possible uses of satellites in these orbits.
In your answer you should explain why:
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a low polar orbit is suitable for a satellite used to monitor conditions on the Earth.
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a geosynchronous circular orbit above the Equator is especially suitable for a
satellite used in communications.
The quality of your written communication will be assessed in your answer.
(6)
(Total 12 marks)
Q8.A radioactive source used in a school laboratory is thought to emit α particles and γ radiation.
Describe an experiment that may be used to verify the types of radiation emitted by the source.
The experiment described should allow you to determine how the intensity of radiation varies
with distance in air or with the thickness of suitable absorbers.
Your answer should include:
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the apparatus you would use and any safety precautions you would take
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the measurements you would make
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how the measurements would be used to reach a final decision about the emitted
radiation.
The quality of your written communication will be assessed in your answer.
(Total 6 marks)
Q9.Many astronomical observations rely on a Charge Coupled Device (CCD) to obtain an image.
Describe the structure and operation of the CCD and discuss the advantages of using a CCD
for astronomical observations.
The quality of your written communication will be assessed in this question.
(Total 6 marks)
Q10.(a)
Sound waves are incident on the ear canal of a normal human ear. Describe the physical
processes involved in the transmission of the energy from the air through to the inner ear.
Include an outline of how the variations in air pressure in the ear canal are amplified to
produce greater pressure variations in the inner ear.
The quality of your written communication will be assessed in your answer.
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(b)
Define intensity of sound.
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(c)
A human ear has a threshold of hearing of 54 dB at a given frequency. Calculate the
intensity of sound incident on the ear at this frequency.
Give your answer to an appropriate number of significant figures.
Io = 1.0 × 10−12 W m−2
intensity of sound ................................... W m−2
(3)
(Total 11 marks)
Q11.(a)
Explain why the compression stroke of a diesel engine is considered to be an adiabatic
change.
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(2)
(b)
Figure 1 shows the cylinder of a diesel engine. The pressure of the air at the start of the
compression stroke is 1.0 × 105 Pa and the volume above the piston is 4.5 × 10−4 m3.
Figure 2
Figure 1
Figure 2 shows the same cylinder at the instant just before the fuel is injected. The pressure
above the piston is now 6.2 × 106 Pa. The compression is adiabatic with no leakage of air past
the piston or valves.adiabatic index
(i)
for air = 1.4
Calculate the volume above the piston at the instant just before the fuel is injected.
Give your answer to an appropriate number of significant figures.
volume ......................................... m3
(3)
(ii)
The temperature of the air in the cylinder at the start of the compression stroke is
297 K. Calculate the temperature of the air at the instant just before the fuel is
injected.
temperature ........................................... K
(2)
(iii)
Explain why, in a diesel engine, the fuel starts to be injected into the cylinder slightly
before the piston reaches its highest point in the cylinder.
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(1)
(c)
Figure 3 shows the indicator (p – V) diagram for a real diesel engine compared to
the p – V diagram for a theoretical diesel cycle of the same maximum and minimum
volumes and fuel injection cut-off.
Figure 3
Compare the real engine cycle with the theoretical cycle. In your account you should:
•
discuss the important differences between the cycles
•
explain why the overall efficiency of the real engine is less than that predicted by an
analysis of the theoretical cycle.
The quality of your written communication will be assessed in your answer.
(6)
(Total 14 marks)
Q12.In his investigation of radio waves, Hertz created stationary waves by using a large flat metal
sheet to reflect radio waves as shown in the diagram below.
(a)
Explain why stationary waves are formed in this arrangement and describe how the
wavelength of the radio waves can be determined by moving a suitable detector along XY.
The quality of your written communication will be assessed in your answer.
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(b)
Hertz knew the frequency of the radio waves from the electrical characteristics of the
transmitter. He found the wavelength from the investigation described in part (a) and was
then able to calculate the speed of the radio waves. Explain the significance of the result
of this calculation.
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(2)
(Total 8 marks)
Q13.
(a) On the figure below sketch a graph to show how the radius, R, of a nucleus varies
with its nucleon number, A.
(1)
(b)
(i)
The radius of a gold-197 nucleus
is 6.87 × 10–15 m.
Show that the density of this nucleus is about 2.4 × 1017 kg m–3.
(2)
(ii)
Using the data from part (b)(i) calculate the radius of an aluminium-27
nucleus,
.
answer = ...................................... m
(2)
(c)
Nuclear radii have been investigated using α particles in Rutherford scattering
experiments and by using electrons in diffraction experiments.
Make comparisons between these two methods of estimating the radius of a nucleus.
Detail of any apparatus used is not required.
For each method your answer should contain:
•
the principles on which each experiment is based including a reference to an
appropriate equation
•
an explanation of what may limit the accuracy of each method
•
a discussion of the advantages and disadvantages of each method.
The quality of your written communication will be assessed in your answer.
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(Total 11 marks)
Q14.
TRAPPIST is a robotic telescope designed to detect exoplanets, which are planets outside
our solar system.
(a)
The charge coupled device (CCD) attached to TRAPPIST has a quantum efficiency of
96% for light of wavelength 750 nm.
Explain what is meant by the quantum efficiency of a CCD.
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(1)
(b)
(i)
The optical arrangement of the telescope includes an objective mirror of diameter
0.60 m.Calculate the minimum angular separation of two objects which can be
resolved by the telescope for light of wavelength 750 nm.
answer = .................................... rad
(1)
(ii)
One of the nearest exoplanets orbits the star Epsilon Eridani, which is 10.5 light
years from Earth. The exoplanet has an elliptical orbit, whose orbital radius varies
from 1 AU to 5 AU.
Calculate the maximum angular separation of the star and the planet when viewed
from a distance of 10.5 light years.
answer = .................................... rad
(3)
(iii)
TRAPPIST detects the presence of exoplanets by measuring the reduction in light
intensity that occurs as the planet passes in front of the star.
Explain why it is unlikely that the telescope could be used to observe such planets
directly.
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(1)
(c)
Different types of telescope are used to detect the various parts of the electromagnetic
spectrum. Discuss with reference to three different parts of the electromagnetic spectrum,
the factors which should be taken into account when deciding the siting and size of
telescopes.The quality of your written communication will be assessed in your answer.
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(Total 12 marks)
Q15.
(a) Explain how and why ultrasound is used to obtain an image of an unborn foetus.
You might consider the following points in your answer
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the method of obtaining the image
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practical considerations for the scan
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safety issues.
The quality of your written communication will be assessed in this question.
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(6)
(b)
Explain why the pulses of ultrasound used in medical imaging must be of short duration.
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(2)
(Total 8 marks)
Q16.
Figure 1 shows a model steam engine used in a school to demonstrate energy
transfers.The steam engine drives a dynamo which requires a constant torque.By means of
valves, high pressure steam is applied to one side of the piston on the outward stroke (as
shown) and to the other side of the piston on the inward stroke. The motion of the piston is
converted to rotary motion by a connecting rod and crank. A flywheel (not shown) is fitted to the
crankshaft.
Figure 1
Figure 2 shows how the torque on the crankshaft due to the engine varies with the crankshaft
angle θ for one rotation of the crankshaft. The broken line shows the constant dynamo torque
required from the output.
Figure 2
(a)
State and explain how you could use Figure 2 to determine the work done by the engine
in one revolution of the crankshaft.
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(1)
(b)
The dynamo has a low moment of inertia.
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Explain why the engine torque varies over a cycle.
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Explain why, in terms of kinetic energy or angular momentum, it is necessary to fit a
flywheel to the crankshaft of the engine.
•
Discuss how the motion of the crankshaft is influenced by the value of the moment
of inertia of the flywheel.
The quality of your written communication will be assessed in your answer.
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(Total 7 marks)
Q17.
(a) Light has a dual wave-particle nature. State and outline a piece of evidence for the
wave nature of light and a piece of evidence for its particle nature. For each piece of
evidence, outline a characteristic feature that has been observed or measured and give a
short explanation of its relevance to your answer. Details of experiments are not required.
The quality of your written communication will be assessed in your answer.
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(b)
An electron is travelling at a speed of 0.890 c where c is the speed of light in free space.
(i)
Show that the electron has a de Broglie wavelength of 1.24 × 10–12 m.
(2)
(ii)
Calculate the energy of a photon of wavelength 1.24 × 10–12 m.
answer = ...................................... J
(1)
(iii)
Calculate the kinetic energy of an electron with a de Broglie wavelength of1.24 × 10–
12
m.Give your answer to an appropriate number of significant figures.
answer = ...................................... J
(2)
(Total 11 marks)
Q18.
A fixed mass of ideal gas at a low temperature is trapped in a container at
constantpressure. The gas is then heated and the volume of the container changes so that the
pressure stays at 1.00 × 105 Pa. When the gas reaches a temperature of 0 °C the volume is
2.20 × 10–3m3.
(a)
Draw a graph on the axes below to show how the volume of the gas varies
withtemperature in °C.
(2)
(b)
Calculate the number of moles of gas present in the container.
answer = .................................moles
(2)
(c)
Calculate the average kinetic energy of a molecule when this gas is at a
temperature of 50.0 °C. Give your answer to an appropriate number of
significant figures.
answer = .........................................J
(3)
(d)
Calculate the total internal energy of the gas at a temperature of 50.0 °C.
answer = .........................................J
(1)
(e)
By considering the motion of the molecules explain how a gas exerts a pressure and why
the volume of the container must change if the pressure is to remain constant as the
temperature increases.
The quality of your written communication will be assessed in this question.
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(6)
(Total 14 marks)
Q19.
(a) On the axes below draw the Hertzsprung-Russell (H-R) diagram, labelling the main
sequence stars, giant stars and white dwarf stars. Complete the vertical axis by labelling a
suitable absolute magnitude scale.
(3)
(b)
Deneb is the brightest star in the constellation Cygnus.
(i)
The black-body radiation curve for Deneb shows a peak at a wavelength
of 3.4 × 10–7 m. Calculate the black-body temperature of Deneb. Give your
answer to an appropriate number of significant figures.
answer = ........................................K
(3)
(ii)
The power output of Deneb is 70000 times greater than the Sun. Calculate theradius
of Deneb.
surface temperature of the Sun = 5700K
answer = .......................................m
(3)
(c)
The spectrum of Deneb contains Hydrogen Balmer absorption lines. Describe how
Hydrogen Balmer absorption lines are produced in the spectrum of a star.
The quality of your written communication will be assessed in this question.
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(Total 15 marks)
Q20.
(a) An ECG trace is to be obtained for a patient. State and explain the procedure and
some design features of the equipment needed to ensure a good trace is obtained.
The quality of your written communication will be assessed in this question.
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(b)
The figure below shows an ECG trace for a healthy person.
(i)
Add a suitable scale and unit to the potential axis.
(2)
(ii)
Add a suitable scale to the time axis.
(1)
(iii)
State the electrical events which give rise to the points:
P ........................................................................................................
R ........................................................................................................
T ….....................................................................................................
(3)
(Total 12 marks)
Q21.
(a)
Newton suggested a theory that light is composed of corpuscles. He used his theory
to explain the refraction of a light ray travelling from air to glass, as shown in Figure 1.
Huygens explained the refraction of light using his own theory that light consists of waves.
Figure 1
(i)
State one reason why Huygens’ theory of light was rejected for many years after
itwas first proposed, in favour of Newton’s corpuscular theory of light.
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(1)
(ii)
Explain why the eventual measurement of the speed of light in water led to
thedefinite conclusion that light consists of waves and not corpuscles.
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(2)
(b)
Young demonstrated that a pattern of alternate bright and dark fringes was observedwhen
light from a narrow single slit passed through double slits, as shown in Figure 2.
Figure 2
Newton’s corpuscular theory predicted incorrectly that just two bright fringes would be
formed in this pattern. Use Huygens’ theory of light to explain why more than two bright
fringes are formed in this pattern.
The quality of your written communication will be assessed in this question.
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(6)
(Total 9 marks)
Q22.
(a) In a thermal nuclear reactor, one fission reaction typically releases 2 or 3 neutrons.
Describe and explain how a constant rate of fission is maintained in a reactor by
considering what events or sequence of events may happen to the released neutrons.
The quality of your written communication will be assessed in this question.
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(7)
(b)
Uranium is an α emitter. Explain why spent fuel rods present a greater radiation hazard
than unused uranium fuel rods.
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(3)
(Total 10 marks)
Q23.
(a) In 1997 a type 1a supernova was observed which contributed to the controversial
conclusion that the expansion of the Universe is accelerating.
Explain why observations of supernovae led to the conclusion that the Universe is
expanding at an accelerating rate and discuss why this conclusion is controversial.
The quality of your written communication will be assessed in this question.
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(6)
(b)
Measurements of the shift in the 21 cm H1 line in the spectrum of galaxy M84 suggests
that it is receding at a velocity of 900 km s–1.
(i)
Calculate the value of the red shift, z, for this galaxy.
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z = ..........................................
(1)
(ii)
Calculate the distance to this galaxy.
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distance = ...................................... Mpc
(2)
(Total 9 marks)
Q24.
(a) On the axes below, sketch the action potential of a nerve cell. Indicate units and
scales on both axes.
(3)
(b)
Explain in terms of ion movement, starting at resting potential, how bioelectrical signals
are produced in muscle fibres.The quality of your written answer will be assessed in this
question.
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(7)
(Total 10 marks)
Q25.
(a) Figure 3 shows the indicator diagram for a theoretical or ideal four-stroke petrol
engine (Otto) cycle.
Figure 1
Use Figure 1 to describe the process that occurs during each of the
parts A to B, B to C,C to D and D to A of the cycle. Describe whether heating or cooling is
taking place, the type of process and whether work is being done on or by the air.
The quality of your written answer will be assessed in this question.
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(6)
(b)
Show, on Figure 2, how the indicator diagram might be expected to appear if
measurements of pressure and volume were made on a real four-stroke petrol engine of
the same volume under operating conditions. The ideal cycle is shown in dashed lines as
a guide.
Figure 2
(2)
(Total 8 marks)
Q26.
Figure 1 shows the probe of a scanning tunnelling microscope (STM) above a metal
surface.
Figure 1
(a)
Explain why electrons can cross the gap between the tip of the probe and the surface,
provided
•
the gap is sufficiently narrow
•
a potential difference is applied between the tip and the surface.
The quality of your written communication will be assessed in this question.
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(6)
(b)
The probe is moved horizontally in a straight line across the surface. As it moves, the
current due to the transfer of electrons between the surface and the probe decreases then
returns to its initial value at the end of the line, as shown in Figure 2.
Figure 2
Explain why the current changes in this way.
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(2)
(Total 8 marks)
Q27.
(a) Sketch, using the axes provided, a graph of neutron number, N, against proton
number, Z, for stable nuclei over the range Z = 0 to Z = 80. Show suitable numerical
values on the N axis.
(2)
(b)
On the graph indicate, for each of the following, a possible position of a nuclide that might
decay by
(i)
α emission, labelling the position with W,
(ii)
β– emission, labelling the position with X,
(iii)
β+ emission, labelling the position with Y.
(3)
(c)
Used fuel rods from a nuclear reactor emit β– particles from radioactive isotopes that were
not present before the fuel rod was inserted in the reactor. Explain why β– emitting
isotopes are produced when the fuel roads are in the reactor.
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(3)
(d)
A nuclear power station is a reliable source of electricity that does not produce
greenhouse gases but it does produce radioactive waste. Discuss the relative importance
of these features in deciding whether or not new nuclear power stations are needed.
The quality of your written answer will be assessed in this question.
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(6)
(Total 14 marks)
Q28.
Modern astronomy relies on the analysis of radiation from many different parts of the
electromagnetic spectrum. Compare the main features of telescopes used to detect radio waves
with those of optical reflecting telescopes. Explain the differences in their resolving and
collecting powers.
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(Total 6 marks)
Q29.
(a) The discovery of photoelectricity and subsequent investigations led to the wave
theory of light being replaced by the photon theory. State one feature of photoelectricity
that could not be explained using the wave theory of light and describe how it is explained
using photon theory.The quality of your written answer will be assessed in this question.
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(6)
(b)
A certain metal has a work function of 2.2 eV.
(i)
Explain what is meant by this statement.
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(ii)
The surface of the metal is illuminated with light of wavelength 520 nm.
Calculate the maximum kinetic energy of electrons emitted from the surface.
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(5)
(Total 11 marks)
Q30.
Charge coupled devices (CCDs) are commonly used in astronomy because of their
highquantum efficiency.
(a)
Describe the structure and operation of a CCD.
You may be awarded additional marks to those shown in brackets for the quality of written
communication in your answer.
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(4)
(b)
Explain what is meant by quantum efficiency, and state a typical value of the quantum
efficiency of a CCD.
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(2)
(Total 6 marks)
Q31.
The figure below shows the design of an X-ray image intensifier.
The main components are labelled A to D. Name each component and state its purpose in the
process of image intensification.
You may be awarded additional marks to those shown in brackets for the quality of written
communication in your answer.
A............................................................................................................................
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B.............................................................................................................................
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C.............................................................................................................................
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D............................................................................................................................
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(Total 8 marks)
Q32.
Describe the main features of the Big Bang theory and the evidence that supports it.You
may be awarded marks for the quality of written communication in your answer.
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(Total 4 marks)
Q33.
The diagram below shows the probe tip of a scanning tunnelling microscope (STM) above
a metal surface. The probe tip is at a constant negative potential relative to the metal surface.
(a)
Explain why electrons can cross the gap between the probe tip and the surface, provided
the gap is sufficiently narrow.
You may be awarded marks for the quality of written communication in your answer.
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(4)
(b)
Describe one way in which an STM is used to investigate a surface.
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(3)
(Total 7 marks)
M1.
(a)
(i)
mg = ke (1)
k=
(ii)
= 61(.3) N m–1 (1)
T=
(1)
(1)
(= 0.667 s)
(= 1.5(0) Hz)
4
(b)
The marking scheme for this part of the question includes an overall
assessment for the Quality of Written Communication (QWC). There
are no discrete marks for the assessment of QWC but the candidates’
QWC in this answer will be one of the criteria used to assign a level
and award the marks for this part of the question.
Level
Descriptor
an answer will be expected to meet most of the criteria in the
level descriptor
Good 3
Mark
range
– answer supported by appropriate range of relevant points
– good use of information or ideas about physics, going
beyond those given in the question
– argument well structured with minimal repetition or
irrelevant points
5-6
– accurate and clear expression of ideas with only minor
errors of spelling, punctuation and grammar
Modest 2
– answer partially supported by relevant points
– good use of information or ideas about physics given in
the question but limited beyond this
– the argument shows some attempt at structure
3-4
– the ideas are expressed with reasonable clarity but with a
few errors of spelling, punctuation and grammar
Limited 1
– valid points but not clearly linked to an argument structure
– limited use of information or ideas about physics
– unstructured
– errors in spelling, punctuation and grammar or lack of
1-2
fluency
0
– incorrect, inappropriate or no response
0
examples of the sort of information or idea that might be used tosupport an argument
•
forced vibrations (at 0.2 Hz) (1)
•
amplitude fairly large (≈ 30 mm) (1)
•
in phase with driver (1)
•
resonance (at 1.5 Hz) (1)
•
amplitude very large (> 30 mm) (1)
•
oscillations may appear violent (1)
•
phase difference at 90º (1)
•
forced vibrations (at 10 Hz) (1)
•
small amplitude (1)
•
out of phase with driver or phase lag of π on driver (1)
[10]
M2.
(a) The candidate’s writing should be legible and the spelling,
punctuation and grammar should be sufficiently accurate for the
meaning to be clear.
The candidate’s answer will be assessed holistically. The answer will be
assigned to one of three levels according to the following criteria.
High Level (Good to excellent): 5 or 6 marks
The information conveyed by the answer is clearly organised, logical and
coherent, using appropriate specialist vocabulary correctly. The form and
style of writing is appropriate to answer the question.
The candidate states that momentum is conserved, supported by reasoning
to explain why the conditions required for momentum conservation are
satisfied in this case.
The candidate also gives a statement that total energy is conserved, giving
detailed consideration of the energy conversions which take place,
described in the correct sequence, when there is an explosion on a body
that is already moving.
Intermediate Level (Modest to adequate): 3 or 4 marks
The information conveyed by the answer may be less well organised andnot fully
coherent. There is less use of specialist vocabulary, or specialistvocabulary may be used
incorrectly. The form and style of writing is lessappropriate.
The candidate states that momentum is conserved, but the reasoning ismuch more
limited.
and/or
There is a statement that (total) energy is conserved, with basicunderstanding that some
energy is released by the explosion.
Low Level (Poor to limited): 1 or 2 marks
The information conveyed by the answer is poorly organised and may not
be relevant or coherent. There is little correct use of specialist vocabulary.
The form and style of writing may be only partly appropriate.
The candidate indicates that either momentum or energy is conserved, or
that both are conserved. There are very limited attempts to explain either
of them.
The explanation expected in a competent answer should include a
coherent selection of the following points concerning the physical
principles involved and their consequences in this case.
Momentum
•
momentum is conserved because there are no external forces
acting on the overall system (probe plus capsule) – or because it’s
free space
•
they are moving in free space and are therefore so far from large
masses that gravitational forces are negligible
•
during the explosion, there are equal and opposite forces acting
between the probe and the capsule
•
these are internal forces that act within the overall system
•
because momentum has to be conserved, and it is a vector, the
capsule must move along the original line of movement after the
explosion
Energy
•
total energy is always conserved in any physical process becauseenergy can be
neither created nor destroyed
•
however, energy may be converted from one form to another
•
the probe is already moving and has kinetic energy
•
in the explosion, some chemical energy is converted into kineticenergy (and some
energy is lost in heating the surroundings)
•
the system of probe and capsule has more kinetic energy than theprobe had
originally, because some kinetic energy is released bythe explosion
max 6
(b)
(i)
conservation of momentum gives (500 × 160)
= 150 v + (350 × 240) (1)
from which v = (−)26(.7) (m s−1) (1)
direction: opposite horizontal direction to larger fragment
[or to the left, or backwards] (1)
3
(ii)
initial Ek = ½ × 500 × 1602 (1) (= 6.40 × 106 J)
final Ek = (½ × 350 × 2402) + (½ × 150 × 26.72) (1) (= 1.01 × 107 J)
energy released by explosion = final Ek − initial Ek (1)
= 3.7 × 106 (J) (1)
4
[13]
M3.
(a) The candidate’s writing should be legible and the spelling, punctuationand
grammar should be sufficiently accurate for the meaning to beclear.
The candidate’s answer will be assessed holistically. The answer will beassigned to one
of the three levels according to the following criteria.
High Level (good to excellent) 5 or 6 marks
The information conveyed by the answer is clearly organised, logical andcoherent, using
appropriate specialist vocabulary correctly. The form andstyle of writing is appropriate to
answer the question.
The candidate provides a comprehensive and logical description of thesequence of
releasing the ball and taking measurements of initial and finalvoltages. They should
identify the correct distance measurement and showa good appreciation of how to use
these measurements to calculate thetime and acceleration from them. Time should be
found from capacitordischarge, using known C and R values. Repeated readings would
beexpected in any answer worthy of full marks, but five marks may beawarded where
repetition is omitted.
Intermediate Level (modest to adequate) 3 or 4 marks
The information conveyed by the answer may be less well organised and
not fully coherent. There is less use of specialist vocabulary, or specialist
vocabulary may be used incorrectly. The form and style of writing is less
appropriate.
The candidate provides a comprehensive and logical description of the
sequence of releasing the ball and taking measurements of the initial and
final voltages. They are likely to show some appreciation of the use of suvat
equations to calculate the acceleration, although they may not recognise the
need to measure a distance.
Low Level (poor to limited) 1 or 2 marks
The information conveyed by the answer is poorly organised and may not
be relevant or coherent. There is little correct use of specialist vocabulary.
The form and style of writing may only be partly appropriate.
The candidate is likely to have recognised that initial and final voltages
should be measured, but may not appreciate the need for any other
measurement. They may present few details of how to calculate the
acceleration from the voltage measurements.
The explanation expected in a competent answer should include acoherent
selection of the following points.
Measurements
•
initial pd across C (V0) from voltmeter (before releasing roller)
•
distance s along slope between plungers
•
final pd across C (V1) from voltmeter
•
measurements repeated to provide a more reliable result
Analysis
(b)
•
time t is found from V1 = V0e-t/RC, giving t = RC ln (V0/V1)
•
from s = ut + ½ at2 with u = 0, acceleration a = 2s/t2
•
repeat and find average a from several results
(i)
RC = 22 × 10–6 × 200 × 103 [or = 4.4 (s)] (1) (4.40)
5.8 = 12.0 e–t/4.40 (1)
gives t = 4.40 ln (12.0/5.8) = 3.2 (3.20) (s) (1)
3
(ii)
(1)
= 0.49 (0.488) (m s–2) (1)
2
[11]
M4.
(a)
(i)
current I
= 20 (A)
11
(ii)
wasted power (I2 R) = 202 × 30 = 1.20 × 104 (W) (12.0 kW)
power output from cables = 500 – 12 = 488 (kW)
or voltage drop along cables = IR = 20 × 30 = 600 (V)
output voltage = 25000 – 600 = 24400 (V)
power output = IV = 20 × 24400 = 4.88 × 105 (W)
(iii)
efficiency
=
= 98 (97.6) (%)
1
(b)
(i)
primary coil must have more turns than secondary
1
(ii)
to reduce heating (I2R) loss [or energy/power/copper loss]
(because) IS > IP
and R is reduced (by use of thicker wire)
max 2
(c)
The candidate’s writing should be legible and the spelling,
punctuation and grammar should be sufficiently accurate for
the meaning to be clear.
The candidate’s answer will be assessed holistically. The answer
will be assigned to one of three levels according to the following criteria.
High Level (Good to excellent): 5 or 6 marks
The information conveyed by the answer is clearly organised, logical
and coherent, using appropriate specialist vocabulary correctly. The form
and style of writing is appropriate to answer the question.
The candidate provides a comprehensive and logical description of the
main principles of the grid system. They should identify I2R heating as
the main cause of energy loss, and know that this can be reduced by using
transformers to raise voltage and therefore decrease current (for the same
power), and that transformers require ac. They may not have referred to
safety and insulation issues that ultimately require the voltage to be reduced
again or to energy losses from transformers.
Intermediate Level (Modest to adequate): 3 or 4 marks
The information conveyed by the answer may be less well organised andnot fully
coherent. There is less use of specialist vocabulary, or specialistvocabulary may be used
incorrectly. The form and style of writing is lessappropriate.
The candidate provides a description of the main features of the grid systemwhich
recognises that heating losses can be reduced by use of transformersto decrease the
current. They should know that transformers require ac.They may not fully explain the
reasoning for the use of a higher voltage andthey are unlikely to refer to safety and
insulation issues that require thevoltage to be reduced again.
Low Level (Poor to limited): 1 or 2 marks
The information conveyed by the answer is poorly organised and may not
be relevant or coherent. There is little correct use of specialist vocabulary.
The form and style of writing may be only partly appropriate.
The candidate recognises that the use of higher voltage will reduce
transmission losses and that transformers need ac. They give a much
weaker account (if any) of the underlying principles.
Incorrect, inappropriate of no response: 0 marks
No answer or answer refers to unrelated, incorrect or inappropriate
physics.
The explanation expected in a competent answer shouldinclude a coherent
selection of the following points concerningthe physical principles involved and
their consequencesin this case.
voltages are changed using transformers, which work with acbut not with dc
ac generation and transmission is therefore essential
current in cables causes joule heating ( or I2R loss)
resistance of cables should be as low as possible
losses are reduced if current in cables can be reduced
current can be reduced (for same power I V) if voltage is increased
the higher the voltage, the smaller the proportion of theinput power that is wasted
high voltage introduces insulation problems and raises safety issues
voltage must be reduced as the supply reaches its consumers
this is done in stages as the supply is moved from overheadcables to underground wires
transformers cause energy losses because they are not perfectly efficient
features are incorporated in the design of transformers to reducelosses from them
max 6
[13]
M5.
(a)
(i)
use of
= gives NS =
= 60 (turns)
1
(ii)
max output power = 0.85 × 0.630 × 230
max number of lamps
[or efficiency =
max number of lamps
=5
(= 123 W)
(no mark for non-integer answer)
(and max IS = 10.3 (A))
gives 0.85 =
=5
]
2
(iii)
fuse prevents transformer from overheating [or prevents transformer from supplying
excessive currents]
1
(iv)
(all of) transformer is disconnected from supply when fuse fails [or fuse in
secondary circuit would leave primary circuit live]
1
(b)
(i)
The candidate’s writing should be legible and the spelling, punctuation
and grammar should be sufficiently accurate for the meaning to be clear.
The candidate’s answer will be assessed holistically. The answer will be
assigned to one of three levels according to the following criteria.
High level (good to excellent) 5 or 6 marks
The information conveyed by the answer is clearly organised, logical and coherent,
using appropriate specialist vocabulary correctly. The form and style of writing is
appropriate to answer the question.
The candidate states that the ac in the coil produces a constantly changing
magnetic field that passes through the ring, causing an emf to be induced according
to Faraday’s law.
The candidate recognises that the induced emf will cause a current to flow in the
ring, that the current is likely be large because the coil acts as a single conductor
with low resistance, and that this current also produces a magnetic field.
The candidate appreciates that Lenz’s law indicates that the direction of the induced
current is such as to produce a magnetic field that will oppose the existing field, and
that the two fields will interact.
The candidate refers to the force that acts on a current-carrying conductor when it is
in a magnetic field and that this force lifts the ring upwards (into an area where the
magnetic field is weaker) until the upwards magnetic force is equal to the
downwards weight of the ring.
Intermediate level (modest to adequate) 3 or 4 marks
The information conveyed by the answer may be less well organised and not fully
coherent. There is less use of specialist vocabulary, or specialist vocabulary may be
used incorrectly. The form and style of writing is less appropriate.
The candidate is familiar with either or both Faraday’s and Lenz’s laws but only
applies one of them to explain what happens in this demonstration. There are
correct references to the two forces that act on the ring, and a reasonable
explanation of why the ring reaches a stable position.
Low level (poor to limited) 1 or 2 marks
The information conveyed by the answer is poorly organised and may not be
relevant or coherent. There is little correct use of specialist vocabulary. The form
and style of writing may be only partly appropriate.
The candidate refers much more superficially to either Faraday’s or Lenz’s law (or to
both of them) but shows some understanding of why the forces acting on the ring
cause it to reach equilibrium.
The explanation expected in a competent answer should include a coherent
selection of the following points concerning the physical principles involved
and their consequences in this case.
Faraday’s law
•
An emf is induced whenever there is a change in the magnetic flux passing
through a conductor.
•
The magnitude of the emf is proportional to the rate of change of magnetic flux
linkage.
•
The induced emf will cause a current to flow in any complete circuit, such as a
single conducting ring.
•
Because the ring is made from aluminium, which is a good conductor, a large
initial current will be induced in it.
Lenz’s law
•
The induced current flows in such a direction as to oppose the increase in
magnetic flux when the current is switched on in the coil.
•
The current produces a magnetic field in the opposite direction to that
produced by the coil.
•
These two (alternating) fields interact like the fields between two facing like
magnetic poles, giving repulsion.
Forces
•
The ring is a current-carrying conductor in a magnetic field, and
consequently it experiences a force.
•
This magnetic force acts upwards, in the opposite direction to the
weight of the ring.
•
As the ring rises, the magnetic field to which it is exposed becomes
weaker as it moves away from the coil.
•
This reduces the induced current, reducing also the magnetic force
on the ring.
•
The ring reaches a stable height when the magnetic force has
decreased to the point where it is equal to the weight of the ring.
6
(ii)
ring would ‘float’ higher [or be expelled upwards]
because (initial) current or emf (induced) in ring is greater
or ring moves into weaker field until magnetic force balances weight [or (initially)
magnetic force exceeds weight]
2
[13]
M6.
(a)
work done (or energy required) per unit mass
in moving a mass from infinity to the point
2
(b)
(i)
ΔV (= – 1.3 – (–62.6)) = 61.3 (MJ kg–1)
energy required (= mΔV) = 1.2 × 104 × 61.3 × 106
= 7.4 × 1011 (J)
to 2SF only
3
(ii)
beyond X, gravitational potential decreases as Moon is approached
[or gravitational field (or force) of Moon will now attract the probe]
1
(iii)
distance from Earth to Sun » distance from Earth to Moon
change in Vsun (or in gsun) over Earth to Moon distance is negligible
value of Vsun (or gsun) is not (significantly) changed by relative positions
of E+M
2
(c)
The candidate’s writing should be legible and the spelling, punctuation and
grammar should be sufficiently accurate for the meaning to be clear.
The candidate’s answer will be assessed holistically. The answer will be assigned to one
of three levels according to the following criteria.
High Level (Good to excellent): 5 or 6 marks
The information conveyed by the answer is clearly organised, logical and coherent, using
appropriate specialist vocabulary correctly. The form and style of writing is appropriate to
answer the question.
The candidate discusses the forces of attraction due to the Earth and due to the Moon,
appreciates that they act in opposite directions, and that the former is generally much
greater than the latter.
The candidate discusses the resultant gravitational field between E and M, understands
that there is a ‘neutral’ point at which the resultant field strength is zero and that this point
is much closer to M than E. It is recognised that this point has to be passed for the journey
to be completed in either direction.There is a discussion of gravitational potential, in which
it is pointed out that the resultant potential rises to a maximum at the neutral point. There
is a reference to the much greater amount of work that has to be done on the spacecraft
to reach this point from E than from M.
Intermediate Level (Modest to adequate): 3 or 4 marksThe information conveyed by
the answer may be less well organised and not fully coherent. There is less use of
specialist vocabulary, or specialist vocabulary may be used incorrectly. The form and style
of writing is less appropriate.
The candidate discusses the forces of attraction due to the Earth and the Moon, and
appreciates either that they act in opposite directions, or that the former is much greater
than the latter. There is a relevant discussion of field strength or potential. The
significance of the neutral point may not be appreciated. The candidate is likely to make
some reference to the work that has to be done on the spacecraft.
Low Level (Poor to limited): 1 or 2 marks
The information conveyed by the answer is poorly organised and may not be relevant or
coherent. There is little correct use of specialist vocabulary. The form and style of writing
may be only partly appropriate.
The candidate has some understanding of the forces that act during the journey but
makes very limited references to the significance of the variation of the gravitational field.
Discussions of gravitational potential and/or work done are likely to be superficial and may
be absent.
The explanation expected in a competent answer should include a coherent
selection of the following points concerning the physical principles involved and
their consequences in this case.
Gravitational forces
•
The spacecraft experiences gravitational attractions to both the Earth and the
Moon during its journey.
•
These forces pull in opposite directions on the spacecraft.
•
Because E is much more massive than M, for most of the outward journey the
force towards E is greater than that towards M.
•
Only in the later stages of the outward journey is the resultant force directed
towards M.
•
On the return journey the resultant force is predominantly towards E.
Gravitational field strength
•
During the outward journey E’s gravitational field becomes weaker and M’s
becomes stronger.
•
The resultant field is the vector sum of those due to E and M separately.
•
A point (X) is reached at which these two component fields are equal and
opposite, giving zero resultant.
•
X is much closer to M than E.
•
Once X has been passed, the spacecraft will be attracted to M by M’s
gravitational field.
•
On the return journey the spacecraft will ‘fall’ to E once it is beyond X.
Gravitational potential
•
The gravitational potential due E increases (i.e. becomes less negative) as the
spacecraft moves away from E.
•
The resultant gravitational potential is the (scalar) sum of those due to E and M
separately.
•
At X the gravitational potential reaches a maximum value before decreasing as
M is approached.
•
In order to reach M on the outward journey, the spacecraft has to be given at
least enough energy to reach X, and vice-versa for the return.
•
Much more work is needed to move the spacecraft from E to X than from M to
X, since a larger force has to be overcome over a larger distance.
6
[14]
M7.(a)
(i)
from which
= 5.73
and rE (= 5.73 × 7370) = 42 200 (km)
height above surface = 42 200 − 6370 = 35 800 or 35 900 (km)
answer to 3SF only
Full solution derived from Newton’s law of gravitation is acceptable
for all 4 marks.
[or Newton ’s law approach for 1st two marks:
∴rE3 =
(=7.54 × 1022)
from which rE = 42 200 (km)
]
For 3 rd mark, final answer must be expressed in km.3SF mark is
independent.
4
(ii)
centripetal force (= m ɷ2r) =
= 4800 (4760) (N)
If both T and r values for the geosynchronous satellite are
substituted, award 0 marks for (ii).
[or centripetal force
and v =
gives v = 7350 (m s−1) and centripetal force =
= 4800 (4760) (N)
]
[or centripetal force
= 4800 (4770) (N)
]
If only one correct T or r value for the polar satellite is substituted,
mark (ii) to max 1.
2
(b)
The candidate’s writing should be legible and the spelling, punctuation and
grammar should be sufficiently accurate for the meaning to be clear.
The candidate’s answer will be assessed holistically. The answer will be assigned to one
of three levels according to the following criteria.
High Level (Good to excellent): 5 or 6 marksThe information conveyed by the answer is
clearly organised, logical and coherent, using appropriate specialist vocabulary correctly.
The form and style of writing is appropriate to answer the question.
Four aspects must be considered in a high level answer:Features of polar orbit.Features of geosynchronous orbit.Why
polar orbit is suitable for monitoring.Why geosynchronous orbit is
suitable for communication.
The candidate gives a comprehensive comparison of the principal features of the satellite
orbits and explains the consequences for the uses of the two types of satellites. There are
clear statements showing good understanding of why the polar satellite is suitable for
monitoring, and of why the geosynchronous satellite is useful for communications.
Intermediate Level (Modest to adequate): 3 or 4 marksThe information conveyed by
the answer may be less well organised and not fully coherent. There is less use of
specialist vocabulary, or specialist vocabulary may be used incorrectly. The form and style
of writing is less appropriate.
The candidate’s comparison of the principal features of the orbits is less complete and the
consequences for the uses of satellites in them are less well understood. The candidate
has an acceptable appreciation of why the polar satellite is suitable for monitoring, and of
why the geosynchronous satellite is useful for communications.
Low Level (Poor to limited): 1 or 2 marksThe information conveyed by the answer is
poorly organised and may not be relevant or coherent. There is little correct use of
specialist vocabulary. The form and style of writing may be only partly appropriate.
The candidate has a much weaker knowledge of the principal features of the orbits and
very limited knowledge of consequences for the uses of satellites in them. Understanding
of why the polar satellite is suitable for monitoring, and why the geosynchronous satellite
is suitable for communications, is limited or absent.
The explanation expected in a competent answer should include a coherent
selection of the following points.
Low polar orbit
•
Orbital period is a few hours
•
•
•
•
•
•
•
•
•
•
•
Earth rotates relative to the orbit
Many orbits with different radii and periods are possible
Orbit height is less than geosynchronous satellite
Speed is greater than that of geosynchronous satellite
Satellite scans the whole surface of the Earth
Applications: surveillance of conditions / installations on Earth, mapping, weather
observations, environmental monitoring
Gives access to every point on Earth’s surface every day
Can collect data from regions inaccessible to man
Contact with transmitting / receiving aerial is intermittent
Aerial is likely to need a tracking facility
Lower signal strength required than that for geosynchronous satellite
Geosynchronous orbit above Equator
•
•
•
•
•
•
•
•
•
•
•
Orbital period matches Earth’ rotational period exactly
Satellite maintains same position relative to Earth
Only one particular orbit radius is possible
Travels west to east above Equator (in same direction as Earth’s rotation)
Orbit height is greater than polar orbit satellite
Speed is less than that of polar orbiting satellite
Scans a restricted (and fixed) area of the Earth’s surface only
Applications: telecommunications generally, cable and satellite TV, radio, digital
information, etc.
Satellite is in continuous contact with transmitting / receiving aerial
Aerial can be in a fixed position
Higher signal strength required than that for polar satellite
max 6
[12]
M8.The mark scheme for this part of the question includes an overall assessment for the Quality of
Written Communication (QWC).
QWC
Descriptor
Mark range
High Level (Good to excellent)
The candidate refers to all the necessary apparatus and records the count-rate at various
distances (or thicknesses of absorber). The background is accounted for and a safety
precaution is taken. The presence of an α source is deduced from the rapid fall in the count rate
at 2 – 5 cm in air. The presence of a ɣ source is deduced from the existence of a count-rate
above background beyond 30 -50 cm in air (or a range in any absorber greater than that of beta
particles, e.g. 3 – 6 mm in Al) or from the intensity in air falling as an inverse square of distance
or from an exponential fall with the thickness of a material e.g. lead. The information should be
well organised using appropriate specialist vocabulary. There should only be one or two spelling
or grammatical errors for this mark.
If more than one source is used or a different experiment than the
question set is answered limit the mark to 4
5-6
Intermediate Level (Modest to adequate)
The candidate refers to all the necessary apparatus and records the count-rate at different
distances (or thicknesses of absorber). A safety precaution is stated. The presence of an α
source is deduced from the rapid fall in the count rate at 2 – 5 cm in air and the ɣ source is
deduced from the existence of a count-rate beyond 30 -50 cm in air (or appropriate range in any
absorber, e.g. 3 -6 mm in Al). Some safety aspect is described. One other aspect of the
experiment is given such as the background. The grammar and spelling may have a few
shortcomings but the ideas must be clear.
To get an idea of where to place candidate look for 6 items:
1.Background which must be used in some way either for a
comparison or subtracted appropriately
2.Recording some data with a named instrument
3-4
Low Level (Poor to limited)
The candidate describes recording some results at different distances (or thicknesses of
absorber) and gives some indication of how the presence of α or ɣ may be deduced from their
range. Some attempt is made to cover another aspect of the experiment, which might be safety
or background. There may be many grammatical and spelling errors and the information may be
poorly organised.
3.Safety reference appropriate to a school setting – not lead lined
gown for example
4.Record data with more than one absorber or distances
5.α source determined from results taken
6.ɣ source determined
1-2
The description expected in a competent answer should include a coherent selection of
the following points.
apparatus: source, lead screen, ruler, ɣ ray and α particle detector such as a Geiger Muller
tube, rate-meter or counter and stopwatch, named absorber of varying thicknesses may be
used.
safety: examples include, do not have source out of storage longer than necessary, use long
tongs, use a lead screen between source and experimenter.
measurements: with no source present switch on the counter for a fixed period measured by the
stopwatch and record the number of counts or record the rate-meter reading
with the source present measure and record the distance between the source and detector (or
thickness of absorber)
then switch on the counter for a fixed period measured by the stopwatch and record the number
of counts or record the rate-meter reading
repeat the readings for different distances (or thicknesses of absorber).
from results taken
this is a harder mark to achieve
it may involve establishing an inverse square fall in intensity in air
or an exponential fall using thicknesses of lead
if a continuous distribution is not used an absorber or distance in
air that would just eliminate ɣ (30-50cm air / 3-6mm Al) must be
used with and without the source being present or compared to
background
use of measurements:
for each count find the rate by dividing by the time if a rate-meter was not used
subtract the background count-rate from each measured count-rate to obtain the corrected
count-rate
longer recording times may be used at longer distances (or thickness of absorber).
plot a graph of (corrected) count-rate against distance (or thickness of absorber) or refer to
tabulated values
plot a graph of (corrected) count-rate against reciprocal of distance squared or equivalent linear
graph to show inverse square relationship in air
analysis:
the presence of an α source is shown by a rapid fall in the (corrected) count-rate when the
source detector distance is between 2 – 5 cm in air
the presence of a ɣ source is shown if the corrected count-rate is still present when the source
detector distance is greater than 30 cm in air (or at a range beyond that of beta particles in any
other absorber, e.g. 3 mm in Al)
the presence of a ɣ source is best shown by the graph of (corrected) count-rate against
reciprocal of distance squared being a straight line through the origin
6
[6]
M9.The marking scheme for this part of the question includes an overall assessment for the Quality of
Written Communication (QWC). There are no discrete marks for the assessment of written
communication but the quality of written communication will be one of the criteria used to assign
the answer to one of three levels.
The candidate’s writing should be legible and the spelling, punctuation and grammar
should be sufficiently accurate for the meaning to be clear.
There are three areas:
Structure: silicon chip into pixels
The candidate’s answer will be assessed holistically. The answer will be assigned to one of
three levels according to the following criteria.
Function: photon incident, electron excited, electron trapped in
potential well, one electron per photon, no of electrons (and
therefore charge) proportional to number of incident photons, after
sufficient exposure charge on each pixel measured and image
produced
Advantage: most will say the QE>70%
High Level (Good to excellent): 5 or 6 marksThe information conveyed by the answer is
clearly organised, logical and coherent, using appropriate specialist vocabulary correctly. The
form and style of writing is appropriate to answer the question.
A 6 mark answer need not be “perfect” but should be substantially
complete, correct and free from major errors. One of the above
points may be missing. Eg charge integration
The candidate provides a comprehensive and logical description of the structure of the CCD.
The answer includes a clear description of how the light causes a release of charge and why
the charge is stored. The answer also includes an explanation of what is meant by quantum
efficiency and a correct value for the q.e. of a CCD.Confusion with the photoelectric effect would
reduce a 6 mark answer to 5.
5 marks may have 2 missing eg silicon chip and charge integration
Intermediate Level (Modest to adequate): 3 or 4 marksThe information conveyed by the
answer may be less well organised and not fully coherent. There is less use of specialist
vocabulary, or specialist vocabulary may be used incorrectly. The form and style of writing is
less appropriate.
4 probably has more than 2 missing or no correct advantage
The candidate provides a comprehensive and logical description of the CCD. The answer
demonstrates some understanding of how the light is used to generate charge. The answer also
includes some reference the efficiency of the CCD or other advantage
Low Level (Poor to limited): 1 or 2 marks.The information conveyed by the answer is poorly
organised and may not be relevant or coherent. There is little correct use of specialist
vocabulary. The form and style of writing may be only partly appropriate.
The candidate demonstrates an understanding that an image is formed on the CCD and that
this image is transferred to a computer.
Zero: Incorrect, inappropriate or no response.
Points that can be used to support the explanation:
•
•
•
•
•
•
•
•
•
The CCD is a silicon chip
The chip is divided into picture elements
Each picture element is associated with a potential well in the silicon
Incident photons are focused on the CCD
The photons cause the release of electrons within the semiconductor
The number of electrons liberated is proportional to the intensity of the light.
Electrons are trapped in the potential wells
An electron pattern is built up which is identical to the image formed on the CCD
When exposure is complete the charge is processed to form an image.
Advantages:High quantum efficiency > 70%Light integration – using long exposure times to
capture faint images.Device can be directly linked to computer for capture and analysis.
6
[6]
M10.(a)
The candidate’s writing should be legible and the spelling, punctuation and grammar
should be sufficiently accurate for the meaning to be clear.
The candidate’s answer will be assessed holistically. The answer will be assigned to one
of three levels according to the following criteria.
Good to Excellent
The information conveyed by the answer is clearly organised, logical and coherent, using
appropriate specialist vocabulary correctly. The form and style of writing is appropriate to
answer the question.
The candidate explains the principles of transfer of vibrations, from mechanical vibration
of the ear drum, through mechanical oscillations of the malleus, incus and stapes acting
as a lever system, producing mechanical vibration of the oval window and then pressure
waves in the fluid in the cochlea. They use the correct names of the relevant parts of the
ear
They then explain the increase in pressure with sensible use of numbers, reduction in
area of about 20 and increase in force of about 1.5, resulting in pressure increase of about
30.
5-6
Modest to Adequate
The information conveyed by the answer may be less well organised and not fully
coherent. There is less use of specialist vocabulary, or specialist vocabulary may be used
incorrectly. The form and style of writing is less appropriate.
The candidate explains some of the principles of transfer of vibrations and mentions some
of the names of the relevant parts of the ear. They talk about the increase in pressure, but
may fail to add relevant numbers
3-4
Poor to Limited
The information conveyed by the answer is poorly organised and may not be relevant or
coherent. There is little correct use of specialist vocabulary. The form and style of writing
may be only partly appropriate.
The candidate explains a principle of transfer of vibrations or explains the increase in
pressure and mentions at least one of the names of the relevant parts of the ear
2-1
Incorrect, Inappropriate or No ResponseNo answer at all or answer refers to unrelated,
incorrect or inappropriate physics.
0
The explanation expected could include the following:Outer ear acts as a funnel
gathering waves into the ear canalpressure waves incident on eardrumeardrum vibrates,
mechanical vibrationsmechanical vibrations passed through a system of three bones
acting as leversmalleus, incus and stapesthe last bone sets the oval window into
mechanical vibrationthis produces pressure waves in the liquidin the cochlea.three bone
lever system increase force by about 1.5 (1.3 to 1.7) times
cross sectional area of the
oval window about 20 (15 to 25) times less than the cross sectional area of the eardrum
larger force / smaller area gives pressure about 30 times greater, (any answer for
pressure, to agree with other values quoted)
(b)
Intensity is the power per unit (cross-sectional) area (in path of the wave)
At normal incidence
2
(c)
rearrange equation to give I =
correct answer 2.5(12) × 10−7 W m−2
correct to 2 sig figs
3
[11]
M11.(a)
(Adiabatic change requires) no heat transfer / energy transfer / heat to escape / heat loss
(to surroundings)
Do not accept heat or energy ‘change’ .
(Compression stroke occurs in short time / very quickly) so no time for heat transfer
(Therefore change can be considered to be adiabatic)
2
(b)
(i)
P1V1γ = P 2V2γ
Significant figure mark is an independent mark
1.0 × 10 5 × (4.5 × 10−4)1.4 = 6.2 × 106 × V21.4
V2 = 2.4 × 10−5 m3
2 sig fig
3
(ii)
use of
CE from b i
If 2.36 × 10−5 m3used for V2, T2 = 966 K
OR use of n = p1 V1 / R T1 and T2 = p2V2 / nR
Leading to T2 = 982 K
2
(iii)
So that the fuel has partially evaporated / started to burn when piston is at top of
stroke (so max pressure obtained when piston is at top of stroke / top dead centre).
Accept ‘diesel’ instead of ‘fuel’
OR If injected at top dead centre. by the time fuel has started to burn, piston would be on
its way down cylinder, (so max possible pressure not obtained).
1
(c)
Good – Excellent
The information conveyed by the answer is clearly organized, logical and coherent, using
appropriate specialist vocabulary correctly. The form and style of writing is appropriate to
answer the question.
The candidate gives a comprehensive account of the differences between the two
cycles,with reasons. There are clear statements relating to the need for induction and
exhaust processes / strokes in a real engine only, that adiabatic processes are not
possible in the real engine, that constant pressure and constant volume processes are
impossible, and / or that the corners of the real engine diagram are rounded.
They will refer to the lower efficiency of the real engine, linking this to the smaller area
loop, or the fact that the pumping loop has to be subtracted from the main loop and/or that
heat transfers occur during compression and expansion and that in the real engine friction
has to be overcome / power has to be expended in driving ancillaries.
5-6
Modest – Adequate
The information conveyed in the answer may be less well organized and not fully
coherent. There is less use of specialist vocabulary or specialist vocabulary may be used
or spelled incorrectly. The form and style of writing is less appropriate.
The candidate’s comparisons are less complete but good understanding is shown of some
of the major differences between the diagrams, with some reasons given.
They should be able to give at least one valid reason for the lower efficiency of the real
engine cycle.
3-4
Poor – Limited
The information conveyed by the answer is poorly organized and may not be relevant or
coherent. There is little correct use of specialist vocabulary.
The candidate is more likely to describe the differences rather than explain them. They
are likely to make reference to the rounded corners, and the induction / exhaust strokes in
the ‘real’ diagram, but not be able to say why these do not exist in the theoretical diagram.
They may not be able to give a valid reason for the lower efficiency of the real engine
cycle, or may give vague reasons in terms of ‘heat losses’ or ‘friction’ without further
detail.
The descriptions and explanations expected in a good answer should include
several of the following physics ideas
•
Real engine needs ‘pumping loop’ at near atmos. pressure for induction and
exhaust
•
Work needed for induction and exhaust – so efficiency lower than theoretical
•
Area of pumping loop has to be subtracted from main loop, hence reducing net work
and hence efficiency of real engine
•
Theoretical cycle needs no pumping loop / same air continuously taken through
repeated cycles
•
Corners rounded on real engine diagram [because valves are needed and take finite
time to open/close]
•
Cooling cannot occur at constant volume in real engine [because piston would have
to stop]
•
Heating does not occur at constant pressure [because impossible to control rate of
burning of fuel during injection]
•
Compression and expansion do not take place infinitely quickly heat is lost;
therefore not adiabatic processes, lowering efficiency
•
Area of loop is smaller for real engine, less work done per cycle so lower efficiency
•
Friction between moving surfaces has to be overcome / energy expended in driving
oil and water pumps, opening and closing valves etc.
•
Always some exhaust gases present in cylinder.
•
Theoretical cycle does not make reference to any mechanism
•
Calorific value of fuel is never fully realised
2-1
[14]
M12.(a)
Quality of written communication:
Good – Excellent
The candidate provides a comprehensive, coherent and logical explanation which recognises
what a stationary wave is and that the conditions for the formation of a stationary wave are
present. They should know that nodes and antinodes are formed at alternate positions along XY
which are equally spaced with nodes every half wavelength. They should know how the
detector is used to locate the position of each node or antinode and how the wavelength is
determined from the distance between two such positions. They may know that the nodes can
be located more accurately than the antinodes and that their chosen two positions should be as
far apart as possible.
Their answer should be well-presented in terms of spelling, punctuation and grammar.
For top band,
explanation = at least b and e
description = at least f, g,h
(5-6 marks)
Modest – Adequate
The candidate provides a logical explanation which recognises what a stationary wave is and
what some of the conditions for the formation of a stationary wave are. They may know that
nodes and antinodes are formed at alternate positions along XY with nodes every halfwavelength. They may know how the detector is used to locate the position of each node or
antinode and how the wavelength is determined from the distance between two such positions.
They may know that the nodes can be located more accurately than the antinodes and that their
chosen two positions should be as far apart as possible.Their answer should be well-presented
in terms of spelling, punctuation and grammar.
For middle band ,
explanation = at least any two of a-e
description = at least any two of f-i
(3-4 marks)
Poor to Limited
The candidate may recognise that the reflector reflects radio waves which then form a
stationary wave pattern with the incident waves. They may be unaware what the conditions for
the formation of a stationary wave are and their understanding of nodes and antinodes may be
poor. They may have some awareness that the stationary wave causes the detector signal to
vary with position along XY and that the wavelength can be determined from this variation
although they might not be able to link the wavelength to the changes of detector position
correctly.
Their answer may lack coherence and may contain a significant number of errors in terms of
spelling and punctuation.
For lowest band,
Any 2 points ,must be 1 of each for 2 marks
The explanations expected in a good answer should include most of the following
physics ideas
Explanation of stationary wave formation;a. radio waves from the transmitter are reflected back towards
the transmitter
b. reflected and incident waves pass through eachother
c. both waves have same frequency (and speed)
andamplitude
d. superposition (of reflected and incident waves)occurs to form
a stationary wave (as above)
e. equally spaced nodes and antinodes formed along XY
Description of measurement of wavelength;f. Detector signal is zero ( or least) along XY atnodes
g. distance between adjacent nodes is ½λ
h. move detector along XY to measure distancebetween
adjacent nodes and double to give thewavelength
i. measure distance over n nodes and divide by n-1to give
distance between adjacent nodes
6
(1-2 marks)
(b)
Speed of radio waves (obtained by Hertz ) is the same as the speed of light
Speed of electromagnetic waves (calculated or predicted by Maxwell) is the same
as the speed of light ( or of radio waves) so radio waves are electromagnetic waves
2
(Total 8 marks)
M13.
(a)
graph starting (steeply) near/at the origin and decreasing in gradient
1
(b)
(i)
(use of density = mass/volume)
mark for top line and mark for bottom line
(allow use of 1.66 x 10-27)
Lose mass line mark if reference is made to mass of electrons
= 2.4(2) × 1017 kg m-3
2
(ii)
= 3.54 × 10-15 m
or
m
m
or
volume = mass/density =
= 3.54 × 10-15 m
2
(c)
The candidate’s writing should be legible and the spelling, punctuation and
grammar should be sufficiently accurate for the meaning to be clear.
The candidate’s answer will be assessed holistically. The answer will be assigned to one
of three levels according to the following criteria.
High Level (Good to excellent): 5 or 6 marks
The information conveyed by the answer is clearly organised, logical and coherent, using
appropriate specialist vocabulary correctly. The form and style of writing is appropriate to
answer the question.
The candidate makes 5 to 6 points concerning the principles of the method, the limitations
to the accuracy and the advantages and disadvantages of a particular method
Intermediate Level (Modest to adequate): 3 or 4 marks
The information conveyed by the answer may be less well organised and not fully
coherent. There is less use of specialist vocabulary, or specialist vocabulary may be used
incorrectly. The form and style of writing is less appropriate.
The candidate makes 3 to 4 points concerning the principles of the method, the limitations
to the accuracy and the advantages and disadvantages of a particular method
Low Level (Poor to limited): 1 or 2 marks
The information conveyed by the answer is poorly organised and may not be relevant or
coherent. There is little correct use of specialist vocabulary. The form and style of writing
may be only partly appropriate.
The candidate makes 1 to 2 points concerning the principles of the method, the limitations
to the accuracy and the advantages and disadvantages of a particular method
The explanation expected in a competent answer should include a coherent
selection of the following points concerning the physical principles involved and
their consequences.
principles
• α scattering involves coulomb or electrostatic repulsion
• electron diffraction treats the electron as a wave having a de Broglie wavelength
• some reference to an equation, for example λ = h/mv ; eV = mv2/2 ; Qq/4πεor = Eα ;
sinϴ = 0.61λ/R
• reference to first minimum for electron diffraction
accuracy
• α’s only measure the least distance of approach, not the radius
• α’s have a finite size which must be taken into account
• electrons need to have high speed/kinetic energy
• to have a small wavelength or wavelength comparable to nuclear diameter, the
wavelength determines the resolution
• the wavelength needs to be of the same order as the nuclear diameter for significant
diffraction
• requirement to have a small collision region in order to measure the scattering angle
accurately
• importance in obtaining monoenergetic beams
• cannot detect alpha particles with exactly 180° scattering
• need for a thin sample to prevent multiple scattering
advantages and disadvantages
• α-particle measurements are disturbed by the nuclear recoil
• Mark for α-particle measurements are disturbed by the SNF when coming close to
the nucleus or electrons are not subject to the strong nuclear force.
• A second mark can be given for reference to SNF if they add electrons are leptons
or alpha particles are hadrons.
• α’s are scattered only by the protons and not all the nucleons that make up the
nucleus
• visibility – the first minimum of the electron diffraction is often difficult to determine
as it superposes on other scattering events
6
[11]
M14.
(a) the percentage of photons hitting the CCD which are detected and/or produce
a signal
1
(b)
(i)
use of
to give
ϴ = λ/D
ϴ = 750 × 10–9/0.60
= 1.25 × 10–6 (rad)
1
(ii)
use of
to give
s = rϴ
ϴ = 5 × 1.5 × 1011
= 7.55 × 10–6
/10.5 × 9.46 × 1015
(rad)
3
(iii)
either
answer (b)(i) is theoretical limit – and in reality resolving power will be much
poorer than this (due to atmosphere etc)
or
planets will be far too dim to see (next to star)
1
(c)
The candidate’s writing should be legible and the spelling, punctuation and
grammar should be sufficiently accurate for the meaning to be clear.
The candidate’s answer will be assessed holistically. The answer will be assigned to one
of three levels according to the following criteria.
High Level (Good to excellent): 5 or 6 marks
The information conveyed by the answer is clearly organised, logical and coherent, using
appropriate specialist vocabulary correctly. The form and style of writing is appropriate to
answer the question.
The candidate provides a comprehensive and logical explanation which considers the
detection of three named parts of the electromagnetic spectrum.
The candidate describes how the optimum siting of a telescope is determined by the effect
the atmosphere and, for full marks, other factors, such as light pollution, have on three
named parts of the electromagnetic spectrum.
They also demonstrate an understanding of how resolving power, and for full marks, the
collecting power, of a telescope is affected by the size of the aperture, and relate the
resolving power to the wavelengths of the three different parts of the electromagnetic
spectrum.
Intermediate Level (Modest to adequate): 3 or 4 marks
The information conveyed by the answer may be less well organised and not fully
coherent. There is less use of specialist vocabulary, or specialist vocabulary may be used
incorrectly. The form and style of writing is less appropriate.
The candidate provides a comprehensive and logical explanation which names two or
three parts of the electromagnetic spectrum and discusses both siting and size for at least
two for 4 marks, or for one of them for 3 marks.
The candidate may recognise that some telescopes need to be in orbit due to the
absorption of some parts of the em spectrum by the atmosphere. They may also discuss
the positioning of telescopes eg they should be high up to reduce absorption of IR. Their
answer may refer to only resolving or collecting power when discussing the
size of telescopes and there may be little attempt or, for three marks, no attempt to relate
resolving power to wavelength.
Low Level (Poor to limited): 1 or 2 marks
The information conveyed by the answer is poorly organised and may not be relevant or
coherent. There is little correct use of specialist vocabulary. The form and style of writing
may be only partly appropriate.
The candidate recognises some telescopes are in orbit, and for two marks, they may
describe a part of the electromagnetic spectrum being detected.They may confuse which
parts of the electromagnetic spectrum are absorbed by the atmosphere and which pass
through. They may make, for two marks a vague reference to the size of telescopes, and
for one mark they may make no reference at all.
Points that can be used to support the explanation:
Siting
• Apart from visible and some parts of the radio wave section, all the other parts of the
em spectrum are significantly absorbed by the atmosphere.
• To reduce the effects of absorption, IR telescopes are often placed in dry areas
and/or very high up.
• UV is significantly absorbed by the ozone layer, so UV telescopes are generally put
into orbit.
• X-ray telescopes are also put into orbit to avoid atmospheric absorption.
• To avoid atmospheric distortion, visible telescopes are often placed high up.
• To avoid interference from terrestrial sources, radio telescopes may be situated
away from centres of population.
• To avoid light pollution, visible telescopes are often placed a long way from centres
of population.
Size
• Telescopes are often built as large as possible in order to increase the collecting
power, which is proportional to the diameter2.
• The diameter of the objective of telescopes is also often as large as possible in
order to improve the resolving power, as minimum angle resolved is proportional to
1/diameter.
6
[12]
M15.
(a) The candidate’s writing should be legible and the spelling, punctuation and
grammar should be sufficiently accurate for the meaning to be clear.
The candidate’s answer will be assessed holistically. The answer will be assigned to one
of three levels according to the following criteria.
High Level (Good to excellent): 5 or 6 marks
The information conveyed by the answer is clearly organised, logical and coherent, using
appropriate specialist vocabulary correctly. The form and style of writing is appropriate to
answer the question.
The answer will discuss the multi-array of transducers in a linear formation and the use of
gel between the skin and the probe will be explained. There will be mention of the
transducers acting as receivers and why ultra sound echoes occur. There will be some
discussion of the processing of the received signal to produce an image. The fact that this
is non-ionising and thus has no known side effects will be included.
Intermediate Level (Modest to adequate): 3 or 4 marks
The information conveyed by the answer may be less well organised and not fully
coherent. There is less use of specialist vocabulary, or specialist vocabulary may be used
incorrectly. The form and style of writing is less appropriate.
The answer will contain at least one property of the probe and either the use of gel or the
transducer acting as a receiver should be discussed. The processing of the signal will be
sketchy, but the reason that ultrasound is safe is likely to be mentioned.
Low Level (Poor to limited): 1 or 2 marks
The information conveyed by the answer is poorly organised and may not be relevant or
coherent. There is little correct use of specialist vocabulary. The form and style of writing
may be only partly appropriate.
There will be a few of the guidance points mentioned, but there will be little cohesion in
the writing.
The explanation expected in a competent answer should include a coherent
selection of the following points concerning the physical principles involved and
their consequences in this case.
Method of obtaining the image
Ultra sound reflected at interface between two different acoustic impedances
Each transducer emits pulse in turn and receives the echoes from the interfaces directly in
line with it
Each echo displayed as a bright spot on screen
The brightness is determined by the intensity of the echo
The y position is determined by the time taken from transmission to the time of the echo
The x position is determined by the position of the transducer
Images are produced at about 25 per second and thus appear as a real time moving
image
Practical considerations
Probe has line of transducers (approx 100)
High frequency ac pulse applied to each transducer in turn
Each transducer has piezoelectric crystal to generate ultra sound
Use of gel between probe and skin to eliminate air
Transducer acts as receiver
Safety
No harmful side effects known – does not use ionising radiation.
Always allow details of other correct probes.
6
(b)
The transducer to be damped/stop oscillating before the echo returns to allow the
transducer to act as a receiver.
(This time is very short) as distances travelled are short
Emitted pulse must cease before echo arrives so that there is no overlapping at
the transducer/ no interference
3
[9]
M16.
(a)
Either W = area under (engine torque) graph from 0 to 2π rad
OR W = area under graph because W = Tϴ
OR W = dynamo torque × 2π
OR W = area under dotted line / dynamo torque because W = Tϴ
1
(b)
The candidate’s writing should be legible and the spelling, punctuation and
grammar should be sufficiently accurate for the meaning to be clear.
The candidate’s answer will be assessed holistically. The answer will be assigned to one
of three levels according to the following criteria.
High Level (Good to excellent): 5 or 6 marks
The information conveyed by the answer is clearly organised, logical and coherent, using
appropriate specialist vocabulary correctly. The form and style of writing is appropriate to
answer the question.
The candidate is aware that at two points in the cycle the engine torque is zero and can
give a reason, perhaps mentioning moments or variation in steam pressure
The candidate identifies the flywheel as a store of rotational kinetic energy and can relate
the energy changes in one cycle to the varying torque and clearly relates the fluctuation in
speed to the value of the M of I of the flywheel.
Alternatively, the candidate states that the flywheel tends to maintain angular momentum
and so takes the crank over the dead centres. The changing torque has the effect of
changing the angular momentum (I∆ω) but if I is large, ∆ω is small.The candidate may go
on to discuss effect of I being very large (e.g long acceleration time from start).
Intermediate Level (Modest to adequate): 3 or 4 marks
The information conveyed by the answer may be less well organised and not fully
coherent. There is less use of specialist vocabulary, or specialist vocabulary may be used
incorrectly. The form and style of writing is less appropriate.
The candidate correctly identifies that a flywheel will make for smoother motion and may
show an understanding that a flywheel acts as an energy reservoir, but may not be able to
link the motion of the flywheel to the engine torque graph. Candidates answering in terms
of angular momentum appreciate that the flywheel’s angular momentum will take it over
the dead centres. The candidate identifies that an increase in moment of inertia gives
smoother running/less variation in speed per cycle. Reasons for the variation in torque
may not refer to moments but candidate may state that torque is zero when crank and con
rod are in line.
Low Level (Poor to limited): 1 or 2 marks
The information conveyed by the answer is poorly organised and may not be relevant or
coherent. There is little correct use of specialist vocabulary. The form and style of writing
may be only partly appropriate.
The candidate may be able to give a reason why the motion is not smooth and can
identify that a flywheel will make for smoother running. There may be some reference to
the flywheel storing energy. They may confuse power or angular momentum with energy.
The explanation expected in a competent answer should include a coherent
selection of the following points concerning the physical principles involved and
their consequences in this case.
•
without flywheel motion will be jerky/unsmooth/cause vibrationsOR flywheel makes
motion smoother/less fluctuation in speed
•
flywheel needed to take crank over dead centres (wtte)
•
because torque is zero at dead centres
•
torque varies because pressure on piston varies
•
because force is in line with c’shaft/ no moment of force about c’shaft
•
flywheel stores rotational kinetic energy when engine torque > dynamo torque
•
flywheel gives up energy when engine torque < dynamo torque
•
flywheel’s ang. momentum takes it over dead centres
•
the greater I, the less the fluctuation in speed over one cycle
•
over one cycle, work done by engine = work needed by dynamo
•
so average engine torque = average dynamo (load) torque
•
torque = rate of change of ang. momentum – high I gives less change in ω.
6
[7]
M17.
(a) The candidate’s writing should be legible and the spelling, punctuation and
grammar should be sufficiently accurate for the meaning to be clear.
The candidate’s answer will be assessed holistically. The answer will be assigned to one
of three levels according to the following criteria.
High Level (Good to excellent): 5 or 6 marks
The information conveyed by the answer is clearly organised, logical and coherent, using
appropriate specialist vocabulary correctly. The form and style of writing is appropriate to
answer the question.
The candidate provides a comprehensive and coherent answer that includes a stated
property of light such as interference or diffraction that can only be explained in terms of
the wave nature of light and a stated property such as photoelectricity that can only be
explained in terms of the particle nature of light. In each case, a relevant
specificobservational feature should be referred to and should be accompanied by
a coherent explanation of the observation. Both explanations should be relevant
and logical.
For full marks, the candidate may show some appreciation as to why the specific feature
of either the named wave property cannot be explained using the particle nature of light or
the named particle property cannot be explained using the wave nature of light.
Intermediate Level (Modest to adequate): 3 or 4 marks
The information conveyed by the answer may be less well organised and not fully
coherent. There is less use of specialist vocabulary, or specialist vocabulary may be used
incorrectly. The form and style of writing is less appropriate.
The candidate provides a logical and coherent explanation that includes a stated property
of light such as interference or diffraction that can only be explained in terms of the wave
nature of light and a stated property such as photoelectricity that can only be explained in
terms of the particle nature of light.
For 4 marks, the candidate should be able to refer to a relevant specific observational
feature of each property, at least one of which should be followed by an adequate
explanation of the observation. Candidates who fail to refer to a relevant specific
observational feature for one of the properties may be able to score 3 marks by providing
an adequate explanation of the observational feature referred to.
Low Level (Poor to limited): 1 or 2 marks
The information conveyed by the answer is poorly organised and may not be relevant or
coherent. There is little correct use of specialist vocabulary. The form and style of writing
may be only partly appropriate.
The candidate provides some relevant information relating to two relevant stated
properties for 1 mark. Their answer may lack coherence and may well introduce irrelevant
or incorrect physics ideas in their explanation.
Points that can be used to support the explanation:
Wave-like nature property
•
property is either interference or diffraction
•
observational feature is either the bright and dark fringes of a double slit
interference pattern or of the single slit diffraction pattern (or the spectra of a
diffraction grating)
•
explanation of bright or dark fringes (or explanation of diffraction grating
spectra) in terms of path or phase difference
•
particle/corpuscular theory predicts two bright fringes for double slits or a
single bright fringe for single slit or no diffraction for a diffraction grating
Particle-like nature
•
property is photoelectricity
•
observational feature is the existence of the threshold frequency for the
incident light or instant emission of electrons from the metal surface
•
explanation of above using the photon theory including reference to
photon energy hf, the work function of the metal and ‘1 photon being
absorbed by 1 electron’
•
wave theory predicts emission at all light frequencies or delayed
emission for (very) low intensity
6
(b)
(i)
m (= mo (1 - v 2 / c 2) –0.5 = 9.11 × 10–31 (1 - 0.8902)–0.5)
(= 1.998 × 10–30 kg) = 2.0(00) × 10–30 kg
(= 1.2(4) × 10–12m)
2
(ii)
= 1.6(0)× 10–13 J
1
(iii)
EK= (m - mo) c2
= (1.998 × 10–30 – 9.11 × 10–31) × (3.0 × 108)2
= 9.78 × 10–14 J
3 sf only
2
[11]
M18.
(a) graph passes through given point 2.2 × 10–3 m3 at 0 °C straight
line with positive gradient
(straight) line to aim or pass through –273 °C at zero volume
2
(b)
(use of n = P V/R T)
1.00 × 105 × 2.20 × 10–3/8.31 × 273
n = 0.0970 (moles)
2
(c)
(use of mean kinetic energy = 3/2 K T)
= 3/2 × 1.38 × 10–23 × 323
6.69 × 10–21 (J)
3 sfs
3
(d)
total internal energy = 6.69 × 10–21 × 0.0970 × 6.02 × 1023 = 390 (J)
1
(e)
The candidate’s writing should be legible and the spelling,punctuation and
grammar should be sufficiently accurate for themeaning to be clear.
The candidate’s answer will be assessed holistically. The answerwill be assigned to one
of three levels according to the following criteria.
High Level (Good to excellent): 5 or 6 marks
The information conveyed by the answer is clearly organised,logical and coherent, using
appropriate specialist vocabularycorrectly. The form and style of writing is appropriate to
answerthe question.
The candidate provides a comprehensive and coherent sequenceof ideas linking the
motion of molecules to the pressure they exerton a container. At least three of the first
four points listed below must begiven in a logical order. The description should also show
awarenessof how a balance is maintained between the increase in speed andshortening
of the time interval between collisions with the wall to maintaina constant pressure.To be
in this band, reference must be made to force being the rate ofchange of momentum or
how, in detail, the volume compensates for theincrease in temperature.
Intermediate Level (Modest to adequate): 3 or 4 marks
The information conveyed by the answer may be less well organised
and not fully coherent. There is less use of specialist vocabulary, or
specialist vocabulary may be used incorrectly. The form and style of
writing is less appropriate.
The candidate provides a comprehensive list of ideas linking the
motion of molecules to the pressure they exert on a container. At least
three of the first four points listed below are given. The candidate also
knows than the mean square speed of molecules is proportional to
temperature. Using this knowledge, an attempt is made to explain how
the pressure is constant.
Low Level (Poor to limited): 1 or 2 marks
The information conveyed by the answer is poorly organised and may
not be relevant or coherent. There is little correct use of specialist vocabulary.
The form and style of writing may be only partly appropriate.
The candidate attempts the question and refers to at least two of the
points listed below.
Incorrect, inappropriate of no response: 0 marks
No answer or answer refers to unrelated, incorrect or inappropriate
physics.
Statements expected in a competent answer should include some ofthe following
marking points.
molecules are in rapid random motion/many molecules are involved
molecules change their momentum or accelerate on collision withthe walls
reference to Newton’s 2nd law either F = ma or F = rate of change ofmomentum
reference to Newton’s 3rd law between molecule and wall
relate pressure to force P = F/A
mean square speed of molecules is proportional to temperature
as temperature increases so does change of momentum or change invelocity
compensated for by longer time between collisions as the temperatureincreases
as the volume increases the surface area increases which reduces thepressure
max 6
[14]
M19.
(a)
main sequence curvature correct
giants and (white) dwarfs correct
absolute magnitude scale correct (from 15 to –10)
3
(b)
(i)
use of λmax T = 0.0029
gives T = 0.0029/3.4 × 10–7
= 8.5 × 103 (K)
3
(ii)
use of PD/PS = σADTD4/(σASTS4)
gives AD/AS = PDTS4/(PS TD4)
= 70000(5700/8500)4
= 1.42 × 104
so rD/rs = √(1.48 × 104) = 119
gives rD = 119 × 6.96 × 108 = 8.28 × 1010 (m)
3
(c)
The candidate’s writing should be legible and the spelling,
punctuation and grammar should be sufficiently accurate for
the meaning to be clear.
The candidate’s answer will be assessed holistically. The
answer will be assigned to one of three levels according to
the following criteria.
High Level (Good to excellent): 5 or 6 marks
The information conveyed by the answer is clearly organised,logical and coherent, using
appropriate specialist vocabularycorrectly. The form and style of writing is appropriate to
answerthe question.
The candidate states that the atmosphere of the star containshydrogen with electrons in
the n = 2 state and includes a cleardescription of the absorption process in the
atmosphere of thestar, with reference to energy jumps corresponding to
specificfrequencies of light. They describe at least one reason for thegap in the spectrum
in terms of the de-excitation process.
Intermediate Level (Modest to adequate): 3 or 4 marks
The information conveyed by the answer may be less well
organised and not fully coherent. There is less use of specialist
vocabulary, or specialist vocabulary may be used incorrectly.
The form and style of writing is less appropriate.
The candidate may not state that electrons start in the n = 2 state.
Only one of the processes, excitation or de-excitation, is
satisfactorily described. There should be some link between
energy and frequency but they may not make a clear reference
to E = hf.
Low Level (Poor to limited): 1 or 2 marks
The information conveyed by the answer is poorly organised
and may not be relevant or coherent. There is little correct
use of specialist vocabulary. The form and style of writing may
be only partly appropriate.
The candidate recognises that changes in electron energy levels are
involved. They may confuse absorption for emission and their
explanation of why the frequency of the light is important may be
vague. There may also be confusion between absorption due to
the star’s atmosphere and the Earth’s atmosphere.
Incorrect, inappropriate of no response: 0 marks
No answer or answer refers to unrelated, incorrect or inappropriate
physics.
Statements expected in a competent answer should includesome of the following
marking points.
•
the atmosphere of the star has hydrogen atoms withelectrons in the n = 2 state
•
light from the star passes through the atmosphere of the star
•
electrons (in the n = 2) are excited into higher energy states
•
they can only absorb certain amounts of energy
•
these certain energies are related to specific frequencies (E=hf)
•
the electrons then de-excite
•
the electrons may de-excite through different energy level changes
•
when the electrons de-excite the light is radiated in all directions
•
this means that the intensity of the light at particular frequenciesis reduced, resulting
in absorption lines
max 6
[15]
M20.
(a) The candidate’s writing should be legible and the spelling,
punctuation and grammar should be sufficiently accurate
for the meaning to be clear.
The candidate’s answer will be assessed holistically. The answer
will be assigned to one of three levels according to the following
criteria.
High Level (Good to excellent): 5 or 6 marks
The information conveyed by the answer is clearly organised,
logical and coherent, using appropriate specialist vocabulary
correctly. The form and style of writing is appropriate to answer
the question.
The candidate accurately describes measures to ensure good
contact between the electrodes and the skin including the use
of conducting gel. The candidate will mention the need for more
than one electrode and the need for the patient to remain relaxed
and still. They will need at least one property of the amplifier.
Intermediate Level (Modest to adequate): 3 or 4 marks
The information conveyed by the answer may be less wellorganised and not fully
coherent. There is less use of specialistvocabulary, or specialist vocabulary may be used
incorrectly.The form and style of writing is less appropriate.
The candidate will include most measures to ensure good contactbetween electrodes and
the skin. They might give a property of theamplifier or mention the need for the patient to
remain relaxed and still.
Low Level (Poor to limited): 1 or 2 marks
The information conveyed by the answer is poorly organised and
may not be relevant or coherent. There is little correct use of
specialist vocabulary. The form and style of writing may be only
partly appropriate.
The candidate will mention electrodes connected to the skin
and might make another sensible comment on the arrangement.
Statements expected in a competent answer should include
some of the following marking points.
To reduce contact resistance
•
sandpaper skin to remove hairs and some dead skin
•
apply conducing gel
•
securely attach more than one electrode
To remove unwanted signals
•
electrodes should be non-reactive
•
patient to remain relaxed and still
•
shielded leads/reducing interference from ac sources
Properties of amplifier
•
amplifier has large input impedance/high gain/low noise
max 6
(b)
(i)
0 marked where line meets axis with maximum value of 1
unit mark mV
2
(ii)
uniform scale starts at 0 and has value 0.7 (0.9 to 0.5)
at end of T wave
1
(iii)
P depolarisation of atria
R depolarisation of ventricles (and repolarisation of atria)
T repolarisation of ventricles
3
[12]
M21.
(a)
(i)
Newton’s other theories were successful (or Newton was
more eminent so Newton’s view was accepted)
alternatives, Huygens’ theory was based on longitudinal
waves which cannot explain polarisation or
Huygens’ theory could not explain sharp shadows
1
(ii)
either
Newton predicted that light travels faster in glass than
in air, Huygens predicted the opposite
or
there was no evidence (for many years) that light travels
slower or faster in glass than in air
the speed of light in water (or glass) was (eventually) found to be
less than the speed of light in air
diffraction/interference observations not conclusive
max 2
(b)
The candidate’s writing should be legible and the spelling,
punctuation and grammar should be sufficiently accurate for the
meaning to be clear.
The candidate’s answer will be assessed holistically. The answer
will be assigned to one of three levels according to the following
criteria.
High Level (Good to excellent): 5 or 6 marks
The information conveyed by the answer is clearly organised,logical and coherent, using
appropriate specialist vocabularycorrectly. The form and style of writing is appropriate to
answerthe question.
The candidate provides a comprehensive, coherent and logicalexplanation which
recognises that the pattern is due to interferenceof light which is a wave property. They
should know that at a brightfringe, the waves from the two slits are in phase and
thereforereinforce each other and this can happen at positions where thepath difference is
zero or a whole number of wavelengths.They may not refer to the need for the waves to
be coherent.Their answer should be well-presented in terms of spelling,punctuation and
grammar.
Intermediate Level (Modest to adequate): 3 or 4 marks
The information conveyed by the answer may be less well organised
and not fully coherent. There is less use of specialist vocabulary,
or specialist vocabulary may be used incorrectly. The form and style
of writing is less appropriate.
The candidate provides a logical explanation which recognises that
interference of light is a wave property. They should know either a
bright fringe is where the waves from the two slits are in phase or a
dark fringe is where they are out of phase by 180° and be aware
there are different positions where these conditions apply. They
may know the general condition for the path difference for a bright
fringe or a dark fringe although they may not recognise that this
condition explains why there are more than two bright fringes.
Their answer should be adequately or well-presented in
terms of spelling, punctuation and grammar.
Low Level (Poor to limited): 1 or 2 marks
The information conveyed by the answer is poorly organised and
may not be relevant or coherent. There is little correct use of
specialist vocabulary. The form and style of writing may be only
partly appropriate.
The candidate recognises that interference of light is a wave
property and that the waves from the two slits reinforce at a
bright fringe or cancel at a dark fringe. They may confuse path
difference and phase difference and their explanation of why
there are more than two bright fringes may be vague or absent.
Their answer may lack coherence and may contain a significant
number of errors in terms of spelling and punctuation.
Incorrect, inappropriate of no response: 0 marks
No answer or answer refers to unrelated, incorrect or inappropriate
physics.
Statements expected in a competent answer should includesome of the following
marking points.
the pattern is due to interference of light from the two slits
interference is a wave property
light from the two slits is in phase at a bright fringe and thereforereinforces
the path difference (from the central bright fringe to the two slits)is zero
either bright fringes are formed away from the centre wherever thepath difference is a
whole number of wavelengths or dark fringesare formed away from the centre wherever
the path difference isa whole number of wavelengths + a half wavelength
the path difference for the mth bright fringe from the centre is mwavelengths where m is
any whole number
since m is any whole number, more than two bright fringes areobserved
max 6
[9]
M22.
(a) The candidate’s writing should be legible and the spelling,
punctuation and grammar should be sufficiently accurate for the
meaning to be clear.
The candidate’s answer will be assessed holistically. The answer will be
assigned to one of three levels according to the following criteria.
High Level (Good to excellent): 5 or 6 marks
The information conveyed by the answer is clearly organised, logical and
coherent, using appropriate specialist vocabulary correctly. The form and
style of writing is appropriate to answer the question.
The candidate can explain the role of the moderator and control rods in
maintaining a critical condition inside the reactor. The explanation is given
in a clear sequence of events and the critical condition is defined in terms of
neutrons. To obtain the top mark some other detail must be included. Such
as, one of the alternative scattering or absorbing possibilities or appropriate
reference to critical mass or detailed description of the feedback to adjust
the position of the control rods etc.
Intermediate Level (Modest to adequate): 3 or 4 marks
The information conveyed by the answer may be less well organised andnot fully
coherent. There is less use of specialist vocabulary, or specialistvocabulary may be used
incorrectly. The form and style of writing is lessappropriate.
The candidate has a clear idea of two of the following:the role of the moderator, the role of
the control rods or can explain thecritical condition.
Low Level (Poor to limited): 1 or 2 marks
The information conveyed by the answer is poorly organised and may not
be relevant or coherent. There is little correct use of specialist vocabulary.
The form and style of writing may be only partly appropriate.
The candidate explains that a released neutron is absorbed by uranium to
cause a further fission. Alternatively the candidate may explain one of the
following:
the role of the moderator, the role of the control rods or can explain the
critical condition.
The explanation expected could include the following events that
could happen to a released neutron.
a neutron is slowed by the moderator
taking about 50 collisions to reach thermal speeds
then absorbed by uranium-235 to cause a fission event
one neutron released goes on to cause a further fission is the critical
condition
a neutron may leave the reactor core without further interaction
a neutron could be absorbed by uranium-238
a neutron could be absorbed by a control rod
a neutron could be scattered by uranium-238
a neutron could be scattered by uranium-235
max 7
(b)
it is easy to stay out of range or easy to contain an α source or ß/γ havegreater range/are
more difficult to screen (1)
most (fission fragments) are (more) radioactive/unstable (1)
and are initially most likely to be beta emitters/(which also) emit γradiation/are
neutron rich/heavy (1)
ionising radiation damages body tissue/is harmful (1)
max 3
[10]
M23.
(a) The candidate’s writing should be legible and the spelling,
punctuation and grammar should be sufficiently accurate for the
meaning to be clear.
The candidate’s answer will be assessed holistically. The answer will be
assigned to one of three levels according to the following criteria.
High Level (Good to excellent): 5 or 6 marks
The information conveyed by the answer is clearly organised, logical and
coherent, using appropriate specialist vocabulary correctly. The form and
style of writing is appropriate to answer the question.
The candidate states that the distance an object is away can be determined
if its absolute magnitude is known and its apparent magnitude is measured.
The candidate also gives a statement that the absolute magnitudes of some
supernovae is known and that evidence shows that the Universe is
expanding at a faster rate than when the supernovae were produced.
Intermediate Level (Modest to adequate): 3 or 4 marks
The information conveyed by the answer may be less well organised and
not fully coherent. There is less use of specialist vocabulary, or specialist
vocabulary may be used incorrectly. The form and style of writing is less
appropriate.
The candidate states that the distance to some supernovae can be
determined, but the reasoning is much more limited.
There is a statement that there is evidence that suggests that the expansion
of the Universe is accelerating and that there is a controversy, but they may
not recognise that Hubble’s Law shows that the supernovae should be
brighter (ie closer).
Low Level (Poor to limited): 1 or 2 marks
The information conveyed by the answer is poorly organised and may notbe relevant or
coherent. There is little correct use of specialist vocabulary.The form and style of writing
may be only partly appropriate.
The candidate recognises that there is a controversy about the expansion ofthe Universe.
They may confuse the two methods of determining distanceand their explanation of why
there is evidence for an accelerating Universemay be vague.
The explanation expected in a competent answer should include a
coherent selection of the following points concerning the physical
principles involved and their consequences in this case.
•
the absolute magnitude of (some) supernovae is known, this allows
supernovae to be used as standard candles
•
using the inverse square law (or from values of absolute
magnitudes) allows the distance to be calculated
•
supernovae are very bright – so they can be seen in very distant
galaxies
•
it has taken billions of years for the light from the most distant
galaxies to reach Earth; these supernovae were therefore produced
when the Universe was young
•
measurement of red shift (to measure velocity) and use of Hubble’s
Law shows that these supernovae are fainter than expected
•
this indicates that the Universe is expanding faster now than when
the supernovae exploded as the light has had to travel further to
reach us than expected by a constant rate of expansion
max 6
(b)
(i)
use of z = v/c
to give z = 900 × 103/3 × 108
= 3(.00) × 10–3 (1)
1
(ii)
use of v = Hd
to give d = v/H
= 900/65 (1)
= 13.8 (1)
2
[9]
M24.
(a)
general shape, must be both positive and negative values (1)
action potential axis scale and unit – allow –70 to +30,or –90 to +20 mV(these values will
be consistent in part a and part b)minimum –90 maximum +45 (1)
time scale and unit 0 to 6 ms – this will depend on curve drawn, pulselasting no less than
1 ms and no more than 6 ms (1)
3
(b)
The candidate’s writing should be legible and the spelling,
punctuation and grammar should be sufficiently accurate for the
meaning to be clear.
The candidate’s answer will be assessed holistically. The answer will be
assigned to one of three levels according to the following criteria.
High Level (Good to excellent): 5 or 6 marks
The information conveyed by the answer is clearly organised, logical and
coherent, using appropriate specialist vocabulary correctly. The form and
style of writing is appropriate to answer the question.
The candidate provides a correct and detailed description of the movement
of ions into and out of the fibre. They include the terms depolarisation and
repolarisation with reference to change in potential. Final mention is made
to the slower process to restore the equilibrium concentrations.
Intermediate Level (Modest to adequate): 3 or 4 marks
The information conveyed by the answer may be less well organised and
not fully coherent. There is less use of specialist vocabulary, or specialist
vocabulary may be used incorrectly. The form and style of writing is less
appropriate.
The description of ion movement and the terms depolarisation and
repolarisation might not be clearly named, but the candidate refers to the
change in potential, although actual values might not be included. There
may be mention of a final movement restoring equilibrium.
Low Level (Poor to limited): 1 or 2 marks
The information conveyed by the answer is poorly organised and may not
be relevant or coherent. There is little correct use of specialist vocabulary.
The form and style of writing may be only partly appropriate.
Some reference to ion movement and a resulting change in potential. One
of the terms depolarisation or repolarisation might be included.
The explanation expected in a competent answer should include a
coherent selection of the following points concerning the physical
principles involved and their consequences in this case.
Points which can be used to support the explanation:
•
at resting potential, high concentration of K+ ions inside and Na+outside
•
when stimulated, membrane becomes permeable to Na+ ionsentering the core
increasing membrane potential
•
good answer will say depolarisation from –70 mV to 0 mV andreverse polarisation
from 0 mV to +30 mV; but allow depolarisationfrom –70 mV to +30 mV
•
membrane becomes impermeable to Na+ ions and permeable to K+ions leaving the
core
•
reducing membrane potential to –70 mV, repolarisation
•
after this, a much slower process returns the axon to itsinitial state with Na+ ions
outside and K+ ions inside
max 7
[10]
M25.
(a) The candidate’s writing should be legible and the spelling,
punctuation and grammar should be sufficiently accurate for the
meaning to be clear.
The candidate’s answer will be assessed holistically. The answer will be
assigned to one of three levels according to the following criteria.
High Level (Good to excellent): 5 or 6 marks
The information conveyed by the answer is clearly organised, logical and
coherent, using appropriate specialist vocabulary correctly. The form and
style of writing is appropriate to answer the question.
The candidate correctly identifies the two adiabatic and two constant
volume processes described in their correct sequence and gives detailed
consideration of where heating, cooling and work transfers take place. The
candidate states that work is done on the gas only in A → B and by the gas
only in C → D, and/or states that the area of the loop is net work done.
There is also some reference to temperatures and pressures increasing
or decreasing
Intermediate Level (Modest to adequate): 3 or 4 marks
The information conveyed by the answer may be less well organised andnot fully
coherent. There is less use of specialist vocabulary, or specialistvocabulary may be used
incorrectly. The form and style of writing is lessappropriate.
The candidate correctly identifies where some of the heat and worktransfers take place
but the answer is much more limited. The adiabaticprocesses may not be named as such,
but there is a statement that work isdone in these processes or that there is no heat
transfer. One processmight be missed out altogether or be incorrect. There may be
reference totemperatures, volumes and pressures increasing or decreasing.
Low Level (Poor to limited): 1 or 2 marks
The information conveyed by the answer is poorly organised and may not
be relevant or coherent. There is little correct use of specialist vocabulary.
The form and style of writing may be only partly appropriate.
The candidate may refer (incorrectly) to the four processes as making up
the four strokes of the engine real engine and some credit may be given if
there is a statement that A → B is the compression stroke and C → D is the
power stroke.
The answer may be written mainly in terms of pressures, volumes and
temperatures increasing or decreasing with little reference to the type of
process or heat or work transfers.
The candidate may relate the answer to a real engine rather than the
theoretical cycle eg ‘the spark occurs at B’
The explanation expected in a competent answer should include a
coherent selection of the following points concerning the physical
principles involved and their consequences in this case.
A to B
work done on air
adiabatic compression
no heat transfer (from air)
temperature rises
B to C
no work done
heating at constant volume
temperature rises (and also pressure)
C to D
work done by air
accept power stroke
adiabatic expansion
no heat transfer (to air)
work done at expense of kinetic energy of molecules
D to A
cooling (or heat rejected) at constant volume
with no work done
temperature falls
accept answers which cover above points and include reference to
piston, cylinder, valves
max 6
(b)
induction and exhaust ‘pumping’ loop shown (1)
loop of smaller area than ideal loop with ‘rounded’ corners (1)
2
[8]
M26.
(a) The candidate’s writing should be legible and the spelling,
punctuation and grammar should be sufficiently accurate for the
meaning to be clear.
The candidate’s answer will be assessed holistically. The answer will be
assigned to one of three levels according to the following criteria.
High Level (Good to excellent): 5 or 6 marks
The information conveyed by the answer is clearly organised, logical and
coherent, using appropriate specialist vocabulary correctly. The form and
style of writing is appropriate to answer the question.
The candidate gives a comprehensive explanation based on the knowledge
that electrons have a wave-like nature so there is a finite probability of
crossing the gap. They should recognise how the transfer of electrons
across the gap is affected by the gap width and why a pd is necessary and
why it should be constant. Their explanation should have the key ideas
linked effectively in an appropriate sequence.
Intermediate Level (Modest to adequate): 3 or 4 marks
The information conveyed by the answer may be less well organised andnot fully
coherent. There is less use of specialist vocabulary, or specialistvocabulary may be used
incorrectly. The form and style of writing is lessappropriate.
The candidate includes the main idea that electrons can transfer or ‘tunnel’across the gap
because they have a ‘wave-like’ nature. They should showawareness that the transfer of
electrons is in one direction only because apd is applied and that the transfer is affected
by the gap width. Theirexplanation should not include contradictory or incorrect physics
ideas (egthe use of electrostatic attraction).
Low Level (Poor to limited): 1 or 2 marks
The information conveyed by the answer is poorly organised and may not
be relevant or coherent. There is little correct use of specialist vocabulary.
The form and style of writing may be only partly appropriate.
The candidate knows that electrons have a wave-like nature and this is
relevant in this context. They may show some awareness of the effect of
the gap width. They may not appreciate why the wave nature of the
electron is relevant here. They may well introduce irrelevant or incorrect
physics ideas in their explanation.
The explanation expected in a competent answer should include a
coherent selection of the following points concerning the physical
principles involved and their consequences in this case.
•
electrons have a wave like nature
•
there is a finite probability that electrons can cross the gap
•
electrons can tunnel across the gap
•
pd is necessary so electrons cross in one direction only (no net
transfer of electrons for zero pd)
•
the narrower the gap, the greater the number of electrons (per
second) that cross the gap
•
electrons transfer from – to +
•
constant pd provides one less variable (to affect the current)
(de Broglie) wavelength is of the order of the gap width
max 6
(b)
as the probe moves along, the gap width increases (as the currentdecreases) then
decreases (as the current increases) (1)
the current decreases (or increases) because the tunnelling effect (orprobability of
crossing the gap) decreases (or increases) (1)
2
[8]
M27.
(a)
graph passes through N = 100 to 130 when Z = 80 (1)
and N = 20 when Z = 20 (1)
2
(b)
(i)
W at Z > 60 just below line (1)
(ii)
X just above line (1)
(iii)
Y just below line (1)
3
(c)
fission nuclei (or fragments) are neutron-rich and therefore
unstable (or radioactive) (1)
neutron-proton ratio is much higher than for a stable nucleus
(of the same charge (or mass)) (1)
β– particle emitted when a neutron changes to a proton
(in a neutron-rich nucleus) (1)
3
(d)
The marking scheme for this part of the question includes an overallassessment for the
Quality of Written Communication (QWC). Thereare no discrete marks for the assessment
of written communicationbut the quality of written communication will be one of the
criteriaused to assign the answer to one of three levels.
Level
Descriptor
an answer will be expected to meet most of the criteria in the
level descriptor
Good 3
Mark
range
– answer supported by appropriate range of relevant points
– good use of information or ideas about physics, going
beyond those given in the question
– argument well structured with minimal repetition or
irrelevant points
5-6
– accurate and clear expression of ideas with only minor
errors of spelling, punctuation and grammar
Modest 2
– answer partially supported by relevant points
– good use of information or ideas about physics given in
the question but limited beyond this
– the argument shows some attempt at structure
3-4
– the ideas are expressed with reasonable clarity but with a
few errors of spelling, punctuation and grammar
Limited 1
– valid points but not clearly linked to an argument structure
– limited use of information or ideas about physics
1-2
– unstructured
– errors in spelling, punctuation and grammar or lack of
fluency
0
– incorrect, inappropriate or no response
0
examples of the sort of information or ideas that might be used to
support an argument:
•
reduction of greenhouse gas emissions is (thought to be) necessary
to stop global warming (1)
•
long term storage of radioactive waste is essential because the
radiation from it damages (or kills) living cells (1)
•
radioactive isotopes with very long half lives are in the used fuel
rods (1)
•
nuclear power is reliable because it does not use oil or gas from
other countries (1)
•
radioactive waste needs to be stored in secure and safe conditions
for many years (1)
conclusioneithernuclear power is needed; reduction of greenhouse gases is a
greaterproblem than the storage of radioactive waste because
1
2
global warming would cause the ice caps to melt/sea levels torise (1)
safe storage of radioactive waste can be done (1)
ornuclear power is not needed; storage of radioactive waste is agreater problem than
reduction of greenhouse gases because
1
2
radioactive waste has to be stored for thousands of years (1)
greenhouse gases can be reduced using renewable energysources (1)
[14]
M28.
3 marks for any of the following 3 features
•
compared with optical reflecting telescopes, radio telescopes:
•
are much longer
•
have a much lower resolving power
•
are not as affected by the atmosphere and so their positioning is less
critical
•
have only one reflecting surface rather than two
•
have a similar structure in that a concave reflecting surface reflects
the em radiation to a detector at the focal point
3
explanations of resolving power
radio telescopes have a lower resolving power:
because the ratio of wavelength to telescope diameter is larger (1)
because radio wavelengths are very much larger than optical wavelengths(even though the
diameters of radio telescopes are larger) (1)
explanations of collecting power:
collecting power depends on the area of the objective which is much largerfor radio telescopes
(depends on the square of the diameter) (1)
3
[6]
M29.
(a)
one feature (1 mark for one of the following)
•
there is a threshold (minimum) frequency (of light) for
photoelectric emission from a given metal
•
photoelectric emission is instant
explanation
•
light consists of photons (or wavepackets) (1)
•
energy of a photon = hf where f is the light frequency (1)
•
work function
of metal is the minimum amount of energy
it needs to escape (1)
•
1 electron absorbs 1 photon and gains energy hf (1)
•
electron can escape if energy gained hf >
(1)
6
(b)
(i)
an electron requires 2.2 eV of energy to escape from the
metal surface (1)
(ii)
photon frequency, f (= c/λ =
) = 5.77 × 10–19 J (1)
photon frequency (= hf) = 6.63 × 10–34 × 5.77 × 1014 = 3.83 × 10–19 J (1)
EK max (= hf – ) = 3.83 × 10–19 – (2.2 × 1.6 × 10–19) (1)
= 3.1 × 10–20 J (1)
5
[11]
M30.
(a)
silicon chip divided into picture elements (pixels) (1)
incident photons release electrons (1)
number liberated proportional to intensity (1)
image identical to electron pattern (1)
when exposure complete, charge processed to give image (1)
4
(b)
ratio of the number of photons falling on a device that produce
a signal to the total number of photons falling on the device (1)
≥70%(for CCD) (1)
2
[6]
M31.
A
scintillator crystal(s)/fluorescent screen (1)
convert X-ray photons into light (1)
B
photocathode (1)
light energy releases electrons (1)
number of electrons released proportional to X-ray intensity (1)
C
anodes (1)
increase energy of the electrons (1)
focus the electrons to form an image (1)
D
fluorescent screen (1)
converts electron energy into light photons (1)
[8]
M32.
main features :
expanding Universe (from single point) (1)
suggest about 15 billion years ago (1)
‘explosion’ - creation of space/matter/time (1)
evidence :
red shift of distant galaxies (1)
in keeping with Hubble’s law (1)
Hubble’s law can be used to age Universe (1)
max 4
QWC 2
[4]
M33.
(a) electrons can behave as waves[or electrons can tunnel across gap] (1)waves can
cross narrow gaps[or non-zero probability of crossing gap] (1)electron waves would be
attenuated too much by large gap[or probability of transfer negligible if gap too wide][or
the narrower the gap, the greater the probability] (1)electron transfer is from – to + (1)
4
QWC 2
(b)
constant height mode:
tip height constant (1)
current varies as gap width changes (1)
image built up as tip moves across surface
[or as tip moves across, a decrease (or increase)
of current means the gap widens (or narrows)] (1)
3
[or constant current mode:
tip height altered (1)
to keep current constant (1)
image built up as above or as tip moves across,
the tip
height rises (or falls) if the surface rises or
falls (1)]
[7]
E2.
It was evident from their attempts at part (a) that during their courses many candidates had
considered the application of conservation of momentum to events involving an explosion. It
was less clear that they had ever considered an explosion that takes place in a moving object,
or considered how conservation of energy applies in an explosion. Consequently, part (a) of the
question proved to be difficult, not least because it was unfamiliar territory for so many. Part (b),
which was formulaic and involved much less original thinking, brought much more success for
the majority.
In part (a) only a very small proportion of the candidates were able to produce answers that
were well organised, coherent, detailed and contained correct physics to merit a ‘high level’
mark of five or six. More answers fell into the ‘intermediate level’ (three or four marks) and even
more into the ‘low level’ (one or two marks). A major failing in most answers was to overlook the
question’s requirement to address the two conservation laws ‘in this instance’. For a high level
answer, it was necessary to consider an explosion on a moving space vehicle travelling in a
straight line in deep space. All of the italicised section is significant. The system has momentum
before exploding (unlike a straightforward recoil example); this momentum has to be conserved
because there are no external forces in deep space. Hence the probe speeds up and the
capsule must be ejected along the original line of movement (although it may not be possible to
tell that this is ‘backwards’ until the calculation has been done). Forces between probe and
capsule during the explosion are equal and opposite, but they are internal forces for the system.
When considering momentum, it was common for candidates to conclude that ‘momentum must
be conserved because momentum is always conserved’.
In the explosion, chemical energy is converted into kinetic energy; this increases the total kinetic
energy of the system, which is shared between probe and capsule. Examiners saw many very
weak answers that showed total confusion – such as momentum being converted into energy,
mass being converted into energy, or energy not being conserved. A serious omission in many
answers was that of the word ‘kinetic’ before ‘energy’, whilst many answers referred to the event
as an ‘inelastic collision’. There was seldom any reference to conservation of the total energy of
the system taken as a whole.
Most candidates recovered from their poor attempts at part (a) to gain all three marks for the
calculation in part (b) (i). There were also many awards of full marks in part (b) (ii), where the
main mistake was to calculate only the kinetic energy of the system (probe + capsule) after the
explosion, and to regard this as the answer to the question. Apparently, the candidates who did
this had not realised that the system had an initial kinetic energy.
E3.
Part (a), which was about a student’s proposed experimental arrangement for measuring
the acceleration of a cylinder down a slope, was also a test of candidates’ quality of written
communication. Answers were rather better than those on the quality of written communication
questions in the 2010 unit 4 examinations. Perhaps this is because candidates now have a
clearer idea about what is expected in this type of question and are making greater efforts to
address these requirements, or perhaps this question may have been more accessible because
it involved an experimental technique. The main errors saw candidates not answering the
specific aspects posed in the question; what procedure should be followed, what measurements
should be taken, and how would these measurements be used to calculate the acceleration?
Less able candidates in particular, ended up writing much of their answer about how the circuit
would work. Common misconceptions over measurements included the need to measure the
mass of the cylinder, or the angle of the slope. Some candidates thought the time should be
measured with a stopwatch rather than by the intended discharge circuit, whilst others thought
there would be value in repeating the measurements for a different angle of slope. The best
answers were usually brief and to-the-point, showing excellent understanding of what this
experiment would involve.
The need to measure the distance from S1 to S2 was sometimes overlooked. The omission of
any reference to the calculation of acceleration was a serious error and tended to limit the mark
that examiners could award. Among the answers making an attempt to show how a could be
determined, a frequent error was to suggest that this could be done by dividing the average
speed by time rather than by dividing the final speed (ie twice the average speed) by time. The
more successful answers were those using s = ut + ½ at2, with u taken to be zero.
Many candidates achieved full marks in parts (b) (i) and (ii), showing confidence in solving an
exponential equation to determine the time and then applying an appropriate uniform
acceleration equation to calculate a. Some of the less convincing attempts to solve the
exponential equation omitted the essential minus sign in t = –RC ln (V/V0). A small proportion of
the candidates used log10 rather than loge, therefore ending up with the incorrect answer.
Many attempts at part (b) (ii) received no credit because the acceleration was found by dividing
the average speed by the time of descent – the error already noted in part (a).
E4.
Most candidates could score only half marks in part (a). There was very little difficulty in (i),
but the most common answers in (ii) and (iii) were 12 kW and 2.4% respectively. These
incorrect answers were the result of just calculating the power dissipated in the cables, instead
of the power transmitted to the factory by them. It seemed that only the most perceptive
candidates appreciated that the power transmitted would be 500 – 12 = 488 kW and therefore
the efficiency of transmission 97.6%.
In part (b)(i) answers which did not address constructional differences (ie referring to turns
ratios) went unrewarded. The expected answer was that the secondary of a step-down
transformer has fewer turns than the primary (whereas a step-up transformer has more
secondary turns than primary turns).
It was essential to make these comparisons for the same kind of transformer: answers such as
‘a step up has fewer secondary turns but a step-down has fewer primary turns’ were not
considered satisfactory.
Part (b)(ii) was generally answered well, with many candidates realising that thicker wire would
have a lower resistance and hence reduce the power lost by heating of the secondary. It was
quite rare to find an answer in which it was stated that this is important in a step-down
transformer because the secondary carries a higher current than the primary. Frequent
misapprehensions were that a thicker wire would have greater resistance (and thereby reduce
the current), and that thicker wire would have a lower resistivity.
Part (c) was used to assess candidates’ quality of written communication. In this type of
question, a large proportion of candidates struggle when trying to present an organised and
coherent piece of writing that answers the main issues raised by the question. Consequently,
the marks awarded were generally low. Relatively few answers could be placed in the high level
category of response.
Perhaps this is to be expected when, as here, the communication question is attempted at the
end of a fairly demanding examination. The main temptation appeared to be to devote most of
the answer to energy losses in a transformer, which had been the topic tested by a
communications question in a principles of power transmission. Clear statements that
transformers will only work continuously with an ac supply and that power loss through heating
of the cables can be reduced if the current is reduced (whilst maintaining the same power) by
increasing the voltage, were uncommon. Good answers were expected to enhance this by
referring to P = I V and P = I2R and outlining the need for voltage reduction on safety grounds at
the consumer’s end, for low resistance cables etc. It appeared that in many centres, this topic
has only been given a very superficial treatment. It was reassuring for examiners to occasionally
come across a good answer, in which the principles involved in power transmission were
discussed in a logical and organised manner.
E5.
The transformer turns ratio equation was familiar territory for most in part (a) (i), but correct
application of the efficiency formula proved to be a greater challenge in part (a) (ii). Many
correct answers were seen, and almost all students knew that the number of lamps has to be an
integer. Most difficulties arose from mixing up data for the secondary coil with that for the
primary (for example, multiplying the primary current by the secondary voltage).
Parts (a) (iii) and (iv) proved to be an exacting test of whether students could think through to
the real reasons or had enough practical experience of transformers to know these
reasons.Many attempts at part (iii) were general answers about the reason for fitting a fuse in
any circuit rather than specifically in a transformer’s circuit. Very few students stated that
transformer coils can overheat and become damaged when they handle excessive currents and
that they therefore need to be protected.
Similarly, it was only a small minority of answers to part (iv) that were properly valid; that
stopping the primary current would isolate the whole transformer from the mains or that a failed
fuse in the secondary circuit would leave the primary live.
Most students find that electromagnetic induction is one of the most demanding topics in the
specification. In these circumstances perhaps it should not be surprising that many of the
attempts to answer part (b) (i) were very disappointing. Even when pointed at a logical and
sequential structured answer by three bullet points, many students could not construct a
coherent, ordered response. In assessing the Quality of Written Communication, one aspect
that must be taken into consideration is the appropriate use of technical terminology. This was
often absent from the responses seen. The term induction has a very special meaning in
physics; magnetic induction involves magnetising a material by applying a magnetic field,
electrostatic induction involves charge separation by applying an electric field, electromagnetic
induction involves producing an emf by applying a changing magnetic field. In all cases, direct
contact is unnecessary. Many answers contained the word ‘induced’ used much more
carelessly than its technical meaning in physics; a current was stated to be induced in the coil
because it was connected to the ac supply, for example. This current was then said to induce a
magnetic field. Many students seemed obsessed by effects in the iron rod, rather than in the
aluminium ring. The aluminium ring was confused with the coil for example ‘the coil is pushed
upwards by the magnetic field’. It was evident that a large proportion of students were familiar
with statements of the laws of electromagnetic induction but could not apply them meaningfully
to explain what happens in this demonstration. The field produced was regularly referred to as
an electric field. The repulsion of the ring was sometimes attributed to Coulomb’s law and the
repulsion between charges. Fleming’s left hand rule was confused with his right hand rule, or
with the right hand grasp rule.
Broadly, an outline plan of an appropriate answer to this question would be along the following
lines. The ac current in the coil produces an alternating magnetic field, which is concentrated in
the iron rod and passes through the ring. This changing magnetic field induces an emf in the
ring. Because the ring is aluminium it is a good conductor and the emf causes a large current in
it. A current-carrying conductor in a magnetic field experiences a force so this current produces
a magnetic field whose direction opposes the applied field. Interaction between these fields
gives a net upwards repulsion of the ring. As the ring moves upwards the magnetic field
becomes weaker and the force on the ring decreases. The ring’s position becomes stable when
the upwards magnetic force balances its weight. Answers written in this fashion were rare but
not difficult to identify and they were rewarded well.
Answers to part (b) (ii) suffered from the same lack of general understanding as the previous
part. It was often realised that the ring would move to a higher position, or be expelled upwards
from the rod. Reasons were less well presented. Reference to a larger induced current (or emf)
in the ring was considered a prerequisite for an acceptable explanation.
E6.
In the definition of gravitational potential (part (a)) the common failings were the omission
ofper unit mass and a wrong direction of displacement – from a point in the field to infinity
instead of in the opposite direction. The calculation in part (b)(i) was usually well rewarded. The
number of significant figures to be quoted in the final answer should have been limited to the
smallest number of significant figures provided in the data, which was 2 in this case. Not all
students realised that, in order to reach the Moon, the minimum increase in gravitational
potential required was the difference between the values at X and at the Earth’s surface, some
thinking that the probe had to be given an increase of 62.6 MJ kg–1 (which would be enough to
remove it to infinity).
Part (b)(ii) had a high proportion of correct answers, usually given in terms of field strength or
gravitational force rather than gravitational potential. A common error here was to state that the
Earth’s field had no effect beyond X. Very few answers to part (b)(iii) scored both marks and
most received no credit at all. The simplistic, incorrect answer – that V is proportional to
1/rimplied that the potential would be negligible at large r – was given by many. The question
had informed students that near the Earth the value of gravitational potential due to the Sun is –
885 MJ kg–1, which is certainly not negligible! The important facts in this part were that the EarthMoon distance is much less than the Earth-Sun distance, so the change in V due to the Sun is
negligible over the distance moved by the probe.
To merit a mark of 5 or 6 (a high level answer) in part (c) the students were expected to make
detailed correct references to all of the four factors mentioned in the question: forces, field
strengths, potentials and the significance of point X. Few were able to do this, and so the
majority of answers fell to the intermediate or low level. The understanding of gravitational
potential was particularly weak, compounded by misinterpretation of the negative sign in a
scalar quantity. It was commonly stated that the gravitational potential of the Earth
is greaterthan the gravitational potential of the Moon; in fact the values are –62.6 and –3.9 MJ
kg–1respectively, so it appears that a large proportion of A level students did not understand that
0 is greater than a negative number. Most answers concentrated on the Earth’s gravitational
field being larger than the Moon’s because of their different masses. Many answers reiterated
the question, without explaining the reasons satisfactorily, and in a coherent, sequenced, well
organised way. Students should have been able to explain why X is closer to the Moon than to
Earth, that work has to be done on the probe only as far as X, and that the larger distance from
the Earth to X, and the average larger force required to get there, imply that more work has to
be done on the probe when travelling to the Moon than when returning to Earth. Loose use of
terminology was a frequent detractor when making these answers: “the Earth’s larger potential
pulls the probe back to Earth”, etc. References to escape speed, which is not very relevant in
the context of this question, were fairly common.
E7.Use of the relation T ε r3/2 provided a swift method to the required answer in part (a)(i), but the
mathematics involved appeared to be beyond the skills of many of the candidates. Answers
which derived an expression for r 3 from first principles, or which quoted r = (GMT2/4π2)1/3directly,
were equally acceptable. The major error in most answers was a failure to subtract the radius of
the Earth from the value of r when finding the height of the satellite. On this occasion the
number of significant figures required in the final answer was three, because all of the data had
been provided to at least 3SF. Following the expectation of recent papers, a large proportion of
answers only included 2SF.
Candidates had been concentrating on the geosynchronous satellite in part (a)(i) and a
proportion of them failed to read the question sufficiently carefully in part (a)(ii), thereby failing to
spot that it was about the polar orbiting satellite. Their responses therefore quoted T and r
values for the geosynchronous orbit, not answering the question set. For those who used
the Tand r values given in the question, this part usually provided two straightforward marks
using F= mω2r, or F = mv2 /r, or F = GMm/r2.
The features of the orbits and the applications of the two types of satellite were quite well
known. This gave most candidates a better opportunity to score a rather better mark on a
communications question in part (b) than has often been the case in previous Unit 4
examinations. Nevertheless, only a few answers giving a comprehensive and coherent
treatment, expected for 5 or 6 marks, were produced. The majority gave some relevant (and
sometimes unrelated) facts and many were written sufficiently well to merit an intermediate level
mark. In the case of the polar orbit, only a minority of answers made any reference to the fact
that the Earth rotates under the orbiting satellite, and that it is this feature which allows the
satellite to provide complete coverage of the Earth’s surface. Other features of the polar satellite
that were often overlooked were that orbits with different radii are possible, that data can be
collected from inaccessible regions, and that contact is intermittent. Features of the
geosynchronous orbit not often mentioned included the fact that the radius of the orbit is unique,
that the direction of travel is west to east and that the signal strength required is higher than that
for a low orbit. A few candidates stated that the orbital period of the geosynchronous satellite is
one year.
E8.On the whole most candidates knew what approach to take and attempted to explain a suitable
experiment. Weak candidates had issues over the language used to answer this question. Often
they would state that the intensity of radiation needs to be calculated rather than a count rate
needs to be recorded. Also they often stated facts instead of describing an experiment. For
example, alpha particles can be stopped by a sheet of paper is a poor substitute for explaining
what data to take and how to interpret the data to arrive at the conclusion that alpha rays are
emitted from the source. Slightly better candidates started to discuss the background radiation
but they did not always carry on to explain how this would be used in the analysis. Safety in the
experiment was usually given but a majority of candidates tended to overstate the precautions
necessary. It was common to see references to remote handling, lead gowns, and keeping
metres away from the source. Only the better candidates could adequately determine that
gamma rays were given out by the source. These either talked about count-rate falling with the
inverse square of distance or they discussed an absorber, which would have eliminated any
beta radiation but still allows some radiation to pass through. The only way to know radiation
passes through is to compare the count-rate with the background radiation. It was this last point
that many candidates missed. Overall candidates seemed to lack planning. They often missed
important considerations and bolted them on at the end. The standard of English still leaves a
lot to be desired. The writing in several cases was virtually illegible and keywords were often
misspelled. Fortunately there were candidates in contrast to this description who performed the
writing task exceedingly well.
E9.This question assessed the student’s quality of written communication. Many answers included all
the relevant points detailed in the specification and correctly described the quantum efficiency.
Some showed a poorer understanding by referring to the photoelectric effect as the process by
which the electrons are excited or by unclear descriptions of the pixels and potential wells.
E10.Part (a) was the QWC question and proved accessible to nearly all the candidates who were able
to write something of relevance and score at least 1 mark. There were a noticeable number of
candidates who were able to order their answers in a logical way and score either 5 or 6 marks.
However, there were many answers spoiled by poor Physics such as the ossicles transferring
the pressure wave through the ear, or the ossicles acting as a pressure multiplier. Some
candidates glossed over the question asked and spent much more of their time talking about
the way that the cochlea transformed the pressure variations into electrical impulses which was
beyond the scope of the question.
In part (b), many candidates were able to look at the unit and suggest that Intensity was power
per unit area, but only a few added at normal incidence to the path of the wave.
Part (c) was answered well by many candidates, but there were still a noticeable number who
failed to look carefully at the information given and realise that the final answer should only be
quoted to 2 significant figures.
E11.In part (a) most candidates were aware that in an adiabatic compression no heat transfer occurs,
strictly from the gas, but as long as they had the idea of zero heat transfer the mark was given.
The second mark was harder to get: candidates had to state or imply clearly that there was no
time for heat transfer – it was not enough simply to say the compression stroke occurred
quickly.
Candidates are well practised in calculations involving pVγ = c and pV / T= c and parts (b) (i) and
(b) (ii) were tackled well by the majority of candidates, though some failed to achieve the
significant figure mark in part (b) (i). Part (b) (iii) proved more difficult – all too many candidates
thought that all the fuel had to be injected into the cylinder before the piston reached the top of
its stroke, or before it was ignited. Some thought there would not be enough space in the
cylinder for the fuel when the piston was at the top of its stroke.
There were some very confident answers to part (c), with a pleasing proportion of candidates
showing a good understanding of both theoretical and real diesel cycles as represented on a p
– V diagram. Candidates did not find it difficult to describe the most important differences, but
many failed to give reasons, some described the differences but gave the wrong reasons for the
differences. A very common misunderstanding was to think that friction accounted for a
difference in the area enclosed by the loops in the diagrams, not realizing that an indicator
diagram is taken before frictional losses are accounted for. The better answers to the efficiency
part of the question mentioned where friction occurred, usually by giving an example (e.g. at the
bearings), and also mentioned the losses due to oil viscosity and / or the work needed to
circulate cooling water. Lower scoring answers simply mentioned ‘friction’, or missed out this
part of the question altogether. Another fairly common misconception was to think that the
theoretical engine cycle must be 100% efficient. Examiners were wary of vague statements
about ‘heat losses’ as there has to be heat loss (i.e. cooling) in the theoretical engine cycle as
well as the real.
E12.(a)
Most candidates made some progress in their description of how to measure the
wavelength although some were unclear about the use of the detector. Quality of written
communication was tested in this question and it is pleasing to see that many candidates
were able to write clearly and logically on this topic. However, candidates were often
unable to recognise the key physics principles involved in the formation of stationary
waves in this situation although they usually recognised the significance of nodes and
antinodes.
Misunderstandings were often seen in their explanations such as nodes at maxima rather
than minima or superposition occurring at antinodes only. Lengthy explanations that were
about double slits interference rather than stationary waves were not uncommon.
(b)
E13.
Many candidates knew that the speed of radio waves was found to be the same or very
close to the speed of light but only a minority appreciated why it was concluded that radio
waves and light are electromagnetic waves.
Only the less able students tried to draw graphs of completely the wrong shape by showing
peaks etc. in part (a). A significant minority however failed to get the mark because they drew
the graph with a horizontal asymptote. Part (b)(i) also scored well. Only the bottom 25% had
difficulty over the use of the density equation or the volume of a sphere. Not many students got
caught out by powers of 10 in the calculation but this could have been because of the ‘show
that’ nature of the question. Part (b)(i) proved to be much more difficult and only the top third of
the students scored the 2 marks. Some unsuccessful attempts showed the equation for the
radius in terms of the atomic mass number but they did not know where to obtain ro from the
information supplied. Part (c) was a good discriminator and the mean mark was between 3 and
4 out of 6. Two thirds of the students supplied information about alpha particles being scattered
electrostatically. Many hinted at the idea that the least distance of approach is connected to a
measure of the radius of the nucleus. This group of students also referred to electrons behaving
as waves to explain diffraction. The bottom third of students scored poorly because they did not
add much information to what they would have covered at GCSE. It was common to see an
explanation of the scattering distribution of alpha particles and give nothing else. In this way
they almost completely ignored the wording of the question. Students had obviously been
taught this section of the specification in a vast number of different ways. To give students the
greatest benefit, no individual marking point was required for any particular score. Any of the
selection of points listed in the marking scheme were noted and taken into consideration along
with the quality of communication. As a consequence, for example, some students scored full
marks even though they did not refer to any equations. Most students lost marks by not
including enough of the points listed. They did not include many statements that were wrong
apart from one notable exception. A majority of students who gave the equation to find the least
distance of approach for an alpha particle related the initial kinetic energy of the alpha particle
with the Coulomb force expression rather than the potential energy expression.
E14.
The definition of quantum efficiency required in part (a) proved to be quite demanding.
Although several alternative answers were given credit, the mark was lost by students who
failed to refer to the photons incident on the CCD in their answer. There were also a significant
number of answers suggesting that the students had not come across the term before.The
calculation in part (b)(i) proved to be very straight forward for the majority of students. There
were some careless mistakes with students inverting the values when substituting them into the
equation, or incorrectly converting nanometres to metres.The calculation in (b)(ii) proved to be
more demanding. Some students had difficulties converting the two distances into the same
unit, despite the conversion factors being provided in the data booklet. Some students were
also confused by the two values of radius quoted, and tried to include them both in their answer
by adding, subtracting or averaging them. The inclusion of the wavelength (750 nm) in answers
was interpreted as a physics error and no credit was given. Another relatively common problem
was due to students calculating their answers in degrees and failing to change the unit in the
answer line, or convert their answer to radian.Whilst there were many very pleasing answers to
(b)(iii), many students failed to get the mark because they assumed that the problem was due to
the angular resolution of the telescope, despite having correctly shown that the angular
separation of the planet and star was greater than the angular resolution of the telescope. Many
correct answers suggested that the planet would be too dim, but there were also many other
approaches that gained credit.Question (c) incorporated the quality of written communication
assessment. Most students were able to write about the telescopes they have studied.
Unfortunately a significant number simply wrote down everything they knew about telescopes
without restricting themselves to three parts of the electromagnetic spectrum, or to siting and
size. Irrelevant material included descriptions of chromatic aberration for example. There was
also evidence for confusion about what parts of the spectrum do get through the atmosphere,
students commonly suggesting that x–ray and gamma–ray telescopes can be ground based, or
that radio telescopes need to be in orbit. There was also confusion between infra red and ultra
violet radiation.
E15.
This question was related to ultrasound scans. Part (a) was the part where written
communication was examined and related to prenatal scans. This was felt to be a topic that the
students would be able to write on in a logical manner, but most answers were lacking in detail
and coherence, with poor spelling and sentence construction. The use of a multi-array probe in
a B-scan was very poorly described and very few answers could be graded in the high level as
good to excellent. Many students still refer to the gel used in ultrasound as ‘Conducting’
confusing this with the gel used in an ecg examination, even suggesting that the patients
stomach should be rubbed with sandpaper to remove unwanted hairs. Many students
suggested that the ultrasound was diffracted or scattered at boundaries. The reasons for the
partial reflections were not often given. The use of the gel to eliminate air was often not
discussed. Students often referred to the scan being safer than using X-rays, but failed to state
that this was because ultrasound is non-ionising. Part (b) provided many students with a single
mark. Very few students related the length of pulse to the short distances travelled and thus the
short time available between the start of the transmitted and reflected pulses. Several students
gave incorrect answers suggesting that the short pulses were used to allow the reflected pulse
to be received before the next pulse was transmitted.
E16.
Part (a) asked students to state and explain how to use a graph of torque against angular
velocity to find work done in one revolution. Many students failed to gain a mark here, mainly
because they wrote only “find the area under the graph” without giving any explanation. All that
was wanted in the way of explanation was to link the area to W = Tθ, or to show that they knew
the area required was the area under either graph between 0 and 2π rad.Although there were
some well-written answers to part (b), covering several of the points in the mark scheme, these
were very few and far between. It was clear that the majority of students were totally
unprepared for this. The question highlighted three areas for discussion, and it was expected
that students would be able to show some understanding, perhaps not of all three but certainly
of one or two. The specification asks for an understanding of the use of flywheels in machines,
and an important use of a flywheel is in smoothing out the otherwise irregular motion in
reciprocating machinery.All too often answers just described in words the T against ω graph of
Figure 3 or said that because the acceleration varies, and T = I α, the torque varies, without
mentioning forces or moments. Many tried to use conservation of energy and/or angular
momentum, not taking into account the fact that the engine drove the flywheel so external
torques and work input were involved. Many wrote that the larger the moment of inertia the
smaller would be the engine speed and vice versa. A significant number drew on the previous
year’s QWC question on the design of a flywheel for maximum energy storage, and a lot of what
they wrote was not relevant here.
E17.
In part (a) it was pleasing to see some well-written accounts that covered most if not all the
relevant facts. Many students failed to support a reasonable or good account of one of the two
properties with a similar account of the other property. Many students who were able to supply a
reasonable ‘wave’ explanation of the double slits experiment often gave a limited account of
photoelectricity as a particle property with little more than a statement of the meaning of the
threshold frequency. Explanations often lacked depth as many students failed to link the
threshold frequency to the work function and the photon energy equation. However, a significant
number of students did provide a brief outline of why interference fringes could not be
accounted for using corpuscular theory or why the threshold frequency could not be explained
using wave theory.
In part (b)(i), many students did not realise the relativistic mass needed to be calculated even
though the speed of the electron was given in terms of the speed of light. In (ii) and (iii),
whereas most students were able to calculate the photon energy in (ii), only the best students
were able to calculate the kinetic energy in (iii). Frequent errors included the use of ½ mv2,
some with the correct mass of the electron and some with its rest mass. A significant number of
students did calculate the total energy correctly but then failed to subtract the rest energy.
E18.
The graph in part (a) was done well by most, but the less able candidates were not careful
in reading the temperature scale and did not place the x-axis intercept at absolute zero. In some
cases they had drawn a curve that had no intercept on the x-axis.
Parts (c) (d) and (e) were tacked well by more able candidates. The less able could only
manage to do part (b) but then started either to substitute the wrong data, eg temperature in °C,
or quote incorrect equations in the parts that followed. It was appreciated that not enough space
was given to answer.
Part (e) allowed almost all candidates to score some marks, but the scores tended to be
grouped in the following way. Less able candidates scored a couple of marks by discussing
movement of molecules but did not go any further because of their poor use of physics in using
phrases such as, ‘the molecules have more energy and so hit each other harder giving more
pressure’.
Some candidates started to use Newton’s second law more effectively and referred to pressure
in a more scientific manner.
The more able candidates could explain how increasing the volume allowed the pressure to
remain constant as the temperature increased in terms of molecular motion.
E19.
Part (a) produced a range of answers with many candidates obtaining full marks, but
others dropping marks through carelessness or lack of detail. It was common to see the
absolute magnitude scale upside down, or marked as relative luminosity. Candidates are
expected to know that the scale goes from +15 to –10. Similar errors to previous years were
seen when drawing the main sequence – some candidates drew it as a line or as a simple
straight band. Others had the ends curving the wrong way. None of these got credit. The
position of the giant stars was generally correct, but the positioning of the white dwarfs strayed
too far to the right in some cases.
The calculation in (b)(i) proved to be relatively straightforward, although some scripts showed
confusion with the ‘m’ in the unit of the Wien constant being interpreted as milli rather than
metre. There was also some evidence that many candidates ignored the requirement for the
answer to be expressed to the correct number of significant figures – two in this case.
There was the opportunity for many careless errors in question (b)(ii). One of the more common
was the use of the incorrect formula for the surface area of a sphere, despite this being on the
equation sheet. This was not a problem for those candidates who chose to answer using a ratio
argument but it was more common to see answers which calculated the power of the Sun and
then used this value to calculate the area, and then radius, of Deneb. Other careless answers
used the wrong value for the radius of the Sun, or used 7000 rather than 70000 for the ratio of
the powers.
Part (c) included the assessment of written communication. Unsurprisingly, perhaps, the content
proved to be more accessible than last year’s question on dark energy. However, there was still
evidence of much confusion. Some candidates suggested that it was the hydrogen itself that
was being absorbed, or that hydrogen Balmer was a type of hydrogen. The best answers made
it clear that light of all wavelengths passed through the atmosphere of the star, described the
absorption process with reference to E = hf, and explained why the gaps were present despite
the energy being re-emitted.
E20.
In part (a), much of what was written did not answer the question clearly. The impression
often given was that this topic had been learnt parrot-fashion from a revision guide, or dictated
notes, because candidates who clearly did not understand what was being measured could
often quote ‘high gain, large input impedance, low noise’ impeccably, without relating it to an
amplifier, often just to the ‘sensors’, or just the ECG machine. Many candidates, presumably
confused by the use of a gel, were drawn into describing some features of an ultrasound scan.
Coupling gel was often used to reduce impedance, matching that of the skin, and sometimes an
A scan was received on the oscilloscope.
Generally, answers were so mixed up with actual features of an ECG scan that it was difficult to
be sure what was being described. Features that seemed to have registered well were the
shaving of the chest and the absolute requirement not to use the right leg. Sometimes it was
clear from the answer that the candidate thought that the electrodes were being used to supply
a voltage to the patient – which is why the leads needed to be screened so as not to shock or
electrocute them. ‘Low noise’ was a giveaway to the poor understanding of other candidates
when it was clear that it was being related to sound. The ECG machine had to be quiet, the
room had not to be noisy either otherwise it would ‘spoil the trace’.
In (b)(i) many candidates gained the unit mark, mV, but the scale mark was often lost by either
placing the zero in the wrong place or by confusing it with that for the nerve action potential.
In (b)(ii) the scale was generally well known, but sometimes it was drawn looking non-uniform
because candidates were trying to relate peaks on the graph to remembered values.
In (b)(iii) there were many answers which gained full marks. Those that lost marks did so
because they did not give the electrical events, but described the resulting movements of the
heart.
E21.
Many candidates did not score the mark in (a)(i) because they gave general statements
which could apply to a comparison of any two individuals rather than referring to Newton’s
greater scientific reputation.
In part (a)(ii), most candidates knew that light travels slower in water than in air but many lost a
mark because they only gave the correct prediction of one of the two theories.
Although considerable variation was seen in the depth of knowledge and understanding of
candidates in part (b), many candidates were able to express their ideas adequately. Relatively
few candidates were hampered by very poor quality of written communication. Most candidates
gained some credit for knowing the light from the two slits produced an interference pattern and
were able to give a simple explanation of why bright and dark fringes were formed. Many
candidates knew that bright fringes were formed where the light waves were in phase but a
significant number of candidates did not indicate the exact phase difference for the formation of
a dark fringe and merely stated that the waves needed to be out of phase. Few candidates were
able to state the correct path difference for a bright fringe or for a dark fringe, often referring to
‘phase’ difference in wavelengths or stating the path difference for a bright fringe as one
wavelength instead of a whole number of wavelengths. The key explanation of why there are
more than two bright fringes was often absent or too vague to gain any credit. The more able
candidates wrote clearly that bright fringes are formed where the path difference is a whole
number of wavelengths and that because the light is diffracted at each slit, there will be several
positions where the path difference condition for a bright fringe is fulfilled.
E22.
This question was a good discriminator. Most candidates, in part (a), knew how the core of
the reactor functions. Some candidates too readily used the wording of the question as their
answer. Others did not refer to neutrons even though this was asked for in the question. One
example of a phrase given by candidates that did not quite answer the question but sounded
reasonable was, ‘the power levels were kept constant by keeping a constant rate of fission
using control rods’. This offers much of what was in the question itself and it does not refer to
neutrons. The quality of the writing was generally good.
Again question (b) was a good discriminator. The majority of candidates were aware that fission
products are normally unstable because they tend to be neutron rich or that they release beta
and gamma rays. Less able candidates thought used fuel meant that they had undergone alpha
emission.
E23.
Part (a) was used to assess Quality of Written Communication. It produced answers
across the whole mark range and was one of the highest discriminators on the paper. The
specification approaches the ideas behind the accelerating Universe as a controversy. There
are two conflicting pieces of evidence about how far away distant galaxies appear to be. Type
1a supernovae can be used as standard candles – they have a distinctive light curve with a well
defined absolute magnitude peak. Using this value (–19.3) and the measured apparent
magnitude peak gives one value of distance. The other measurement comes from red-shift and
Hubble’s Law. Measurements of the light from distant galaxy show a shift towards the red end
of the spectrum. The Doppler equation allows the recessional velocity and, using v = Hd, the
distance can be calculated. These two values are not compatible. Essentially, high red shift
supernovae are fainter than they should be. This is interpreted as evidence for an accelerating
Universe. The controversy is that there is no known mechanism driving this acceleration –
which is why cosmologists are using ideas such as dark energy to try to account for it.
Some candidates were able to describe the two methods of measurement, their incompatibility
and the controversial nature of theories needed to explain the accelerating Universe, using
correct spelling, punctuation and grammar and the correct scientific terms. Candidates who did
this obtained full credit. It was common to see answers which only described one measurement
or simply described what supernovae were. Very poor answers suggested that measurements
of distance and velocity were made of the same supernova over a period of time and that this
resulted in acceleration. Similar poor answers implied that Hubble’s Law is an indication of
acceleration, as more distant objects are moving faster.
The inclusion of these ideas on the specification give students an opportunity to look into
aspects of cosmology which are at the forefront of our understanding of how the Universe
works. Questions on this, however, are likely to be limited to the ideas discussed in this report.
Part (b) (i) was one of the most accessible on the paper. The common difficulty for those who
did not obtain full marks was due to a difference in units for the velocity of the galaxy and the
velocity of light.
Part (b) (ii) was also very accessible. Again the most common error was with the unit of velocity.
Having changed it to m s–1 for part (i), several candidates did not use the correct unit for
Hubble’s Law. This usually resulted in candidates not gaining one of the available marks.
E24.
Part (a) was about the action potential of a nerve, but a significant number of candidates
sketched the ecg trace, and a small number sketched the action potential of the heart. If the
correct shape was drawn, then most candidates were able to score the marks for labelling the
axes with the correct scale and unit.
In part (b) there were quite a few candidates who used about three quarters of the space
available talking about the sodium potassium pump getting the muscle into equilibrium and then
tried to squeeze the action potential into two lines at the end. There were some good
descriptions of the ion movements, but the majority of candidates answers fell within the middle
strand as shown in the mark scheme. The main faults were not using specific physics terms
such as depolarisation, reverse polarisation and repolarisation, or not relating the ion movement
with specified changes of potential.
E25.
In part (a), candidates were asked to write an extended descriptive answer on the ideal
petrol engine (Otto) cycle, and they were told that the quality of their written answers would be
assessed. There were some extremely well written, concise and correct answers which even
included application of the first law of thermodynamics to each process, but these were very few
and far between. The best answers were those that concentrated on the processes and not on
the workings of an engine. In an ideal cycle a fixed mass of air is taken through the four
processes irrespective of any kind of mechanism, or any particular method of providing the
heating. Common errors were thinking that the compression and/or expansion were isothermal,
that work is done during a constant volume process, that the ‘spark occurs at point C’, and that
the four processes represented the four strokes of the engine. Most candidates seemed to
appreciate that they were expected to express their ideas in sentences rather than a series of
terse notes.
In part (b) there were some well-drawn diagrams showing a good knowledge of what a real
indicator diagram looks like, but many candidates concentrated only on drawing a loop with
rounded corners, not realising that in the real engine the area of the loop would be less than the
area of the ideal cycle. Many candidates completely missed out a line or narrow loop for the
induction and exhaust strokes, and some drew a cycle for an engine of considerably different
maximum and minimum volumes than the ideal.
E26.
In (a) most candidates found it difficult to score high marks. Only about a quarter of
candidates reached the high or intermediate levels and about a quarter of the candidates
scored zero marks. The main reason was that the candidates did not say or realise that the
essential point of this answer was that the electrons were behaving as waves. Very few realised
the significance of the pd many saying that a high pd is required to pull the electrons across the
gap.
In part (b), the majority of candidates could score one mark by saying that the current
decreases as the gap between the probe and surface widens, but did not go on and link it to
probability or tunnelling.
E30.
The structure and operation of a CCD in part (a) has been asked before and this year
many candidates obtained full marks by simply restating the mark scheme from previous
papers. Several incorrect answers implied that the pixels emit photons or suggested that the
process of analysis is continuous. It was clear that many candidates had no idea what was
happening, suggesting that some centres had not taught this topic. It would be worth searching
the Internet for animations of how a CCD works to help explain the important processes
involved.
In part (b) the best answers quoted the general form of the definition for quantum efficiency,
although answers, which were based on the CCD, were allowed. Most candidates knew that the
value is greater than 70% and a wide range of values greater than this were accepted.
E31.
Some candidates were able to answer this question clearly and concisely, earning all eight
marks. Quite a few lost two marks by turning electrons into photons, rather than the electron’s
energy into photons, and vice versa. The remainder, which was the majority, found the question
difficult and guessed at many of the answers.
E32.
Unfortunately this was incorrectly labelled in the paper but this printing error did not cause
candidates any problems. Almost all candidates managed to write something about the Big
Bang. Those who gained no credit included candidates who described the processes in a
supernova. The expansion of the Universe also caused problems with some students. It was
commonly suggested that everything was expanding and that Hubble’s red shift was measured
for stars, with no mention of galaxies. Background radiation was often given as evidence for the
Big Bang, but this was not given credit unless it was made clear what form this radiation takes.
The inclusion of this subject in the Specification gives candidates the opportunity to read about
one of the most important theories in modern cosmology. Unfortunately too many answers were
vague and ambiguous and suggested little more knowledge or understanding than that of the
general public.
E33.
Although most candidates knew in part (a) that electrons crossed the gap in the scanning
tunnelling microscope because of the wave nature of the electron, they usually referred to
tunnelling and probability rather than attenuation of the wave. Many candidates knew that the
probability of an electron crossing the gap was greater the narrower the gap. The best
candidates were able to explain satisfactorily why a potential difference was necessary although
many candidates considered the potential difference caused insulation breakdown between the
tip and the surface.
Very few good answers were seen in part (b). Most candidates knew that the tunnelling current
varied according to the gap width but few gave a clear answer in terms of a constant current or
the tip being at a constant height. Many candidates switched from constant current to constant
height, often as a result of confusion about feedback giving a constant gap width. Some
candidates failed to mention that the current or the tip height was monitored as the tip was
scanned across the surface.