DO PHYSICS ONLINE
QUESTIONS & PROBLEMS
IDEAS TO IMPLEMENTION
How to answer a question: problem solving (t0_372.pdf)
View periodic table
(cited Aug 2012)
Numerical values for constants and useful physical quantities)
Don’t view a solution until a genuine effort has been made to answer the question or solve the problem.
Answers to problems
p1.23 08/12
The debate as to whether cathode rays are charged particles or electromagnetic waves continued
for many years. Which observation of cathode rays resolved this debate? Clearly distinguish the
wave and particle properties.
p1.28 07/24
(a) A negatively charged cylinder is
fixed in position near a positively charged
plate. Sketch the electric field lines
between the cylinder and the plate.
(b) A tiny particle of mass 10-30 kg and
charge +6×10-12 C is released at point Y.
The particle initially accelerates at 7.0×1021 m.s-2. Calculate the electric field intensity at Y.
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p1.30 06/12
A charged non-magnetic particle is moving in a magnetic field. What factors affect the magnetic
force on the particle?
p1.34 4
An electron is moving near a long straight wire. When a current is applied to the wire the electron
experiences a force in the same direction as the current flow in the wire. What was the electron’s
initial direction of motion? Explain.
p1.44 08/23
Two parallel metal plates were in a magnetic field B
= 1.2310-3 T. The plates were separated by a
distance d = 22.5 mm. An electron was accelerated
by a 10.5 kV before entering the region between the
plates.
e
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d
(a) What was the speed of the electron upon
B
entering the region between the plates?
uniform magnetic field out of page
(b) What was the magnitude and direction of the
force due to the magnetic field?
(c) What was the magnitude and direction of the force due to the electric field if the electron
continued on a straight path parallel to the plates?
(d) What was the magnitude and direction of the electric field between the plates?
(e) What was the voltage between the plates? Which plate was positively charged?
(f) How was this set-up used by J. J. Thompson used to measure the q/m ratio for an
electron?
p1.65 04/12
A discharge is shown.
(a)
(b)
(c)
(d)
(e)
What type of pattern is shown?
What end is the cathode?
Explain the pattern observed?
If the gas was changed, does the pattern change significantly?
If the pressure was changed, does the pattern change significantly?
p1.68 01/2
A positively charged particle is moving with velocity v in
a magnetic field. At this moment, what is the direction of
the force on the positively charged particle? Explain.
Describe the subsequent motion of the particle.
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p1.71
The diagram shows four discharge
tubes and the patterns of striations
observed in them.
(a) Explain the patterns.
(b) Account for the difference in the
striation patterns.
(c) List the tubes in order of
decreasing pressure.
p1.75 7
A charged non-magnetic particle is moving in a magnetic field. What would NOT affect the
magnetic force on the particle?
(a) The strength of the magnetic field.
(b) The magnitude of the charge on the particle.
(c) The velocity component parallel to the magnetic field direction.
(d) The velocity component perpendicular to the magnetic field direction.
Explain each alternative.
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p1.76 02/13
(a)
What is the name of the device shown below?
(b)
What is the purpose of the device?
(c)
What is the name and function of the parts labeled A to F?
E
D
A
B
F
E
C
In a special investigation, the voltage between the cathode and the anode is
increased so that an electron gains a velocity of 0.60 c, where c is the speed of
light. The electron starts from rest at the cathode.
(d)
What was the accelerating voltage for the electron gun?
The deflection plates are separated by a distance of 18 mm and the voltage across them is 254
V.
(e)
(f)
(g)
What is strength of the electric field between the plates?
What is the electric force acting on an electron?
What acceleration of the electron?
p1.79 10
An electron travels at 2.0107 m.s-1 in a plane perpendicular to a 0.0100 T magnetic field.
(a)
(b)
(c)
(d)
Describe the path of the electron.
Calculate the radius of the circular orbit.
Calculate the period of motion.
Calculate the frequency of the electron.
Hint: Centripetal force FC = m v2 / R
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p1.93 1
A potential difference of 50 V is applied between two identical, parallel aluminum plates
which are separated by a distance of 10 mm. In order to double this electric field strength,
which new arrangement should be used?
Explain.
p1.94 K
Crookes developed a gas discharge tube to investigate the electrical nature of matter. When a
high voltage is applied to the tube, the glass behind the metal cross glows (fluoresces) and a
shadow of the cross appears.
(a)
Explain the appearance of the shadow. If the cross is allowed to drop to the horizontal
position, describe and explain the pattern observed.
(b)
Explain the fluoresces of the glass.
(c)
When a magnet is moved towards the gas discharge tube, the shadow moves and is
distorted. Explain.
(d)
How did the use of discharge tubes by scientists contribute to the understanding of
atomic structure?
(e)
You have performed investigations using discharge tubes. Explain how you were able
to get them to function.
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p2.05 07/27
Describe the experiment used by Hertz and his observation of the photoelectric effect. What
did he do about these observations.
p2.06
Describe how Einstein used the ideas of Planck to explain the photoelectric effect.
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p2.08
An experiment was performed using a photocell. The surface was illuminated by light of
different frequencies and the stopping voltage was measured.
Define each of the terms: stopping voltage, threshold frequency, threshold wavelength, work
function of the surface.
(a)
What is Einstein’s equation of conservation of energy explaining the photoelectric
effect in terms of the stopping voltage and frequency?
wavelength
(nm)
stopping
voltage (V)
360
400
440
490
550
580
1.45
1.12
0.95
0.60
0.40
0.25
(b)
Plot the stopping voltage versus the frequency of the light.
(c)
Determine: the threshold frequency, threshold wavelength, the work function in eV
and J, and the value of Planck’s constant.
(d)
Another surface was used in the experiment. Its work function was 0.5 eV. Draw a
line on the graph for this surface.
p2.13 05/12
The family of curves below shows the
relationship between the intensity of black
body radiation and its wavelength for
various Kelvin temperatures.
Who was the first to correctly explain this
relationship?
What information do the graphs give you?
p2.33 07/27
Scientists tried to explain observations of blackbody radiation using classical wave theory and
then quantum theory.
(a)
What is meant by the term blackbody radiation?
(b)
What was a limitation of classical wave theory that could not explain blackbody radiation?
(c)
How does quantum theory satisfactorily explain blackbody radiation?
p2.50 08/24
How did Einstein’s theory of special relativity and his explanation of the photoelectric
effect lead to the re-conceptualisation of the model of light?
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p2.61 08/13
What is the energy of a photon (joules and electron volts) of wavelength 550 nm?
What is the frequency and what part of the electromagnetic spectrum for this photon?
p2.62 02/15
A student carried out an experiment during which light of different frequencies was
shone onto a metal surface to produce electrons. The student measured the maximum kinetic
energy of the emitted photoelectrons as the frequency of light was altered.
(a)
How did the student measure the maximum kinetic energy?
(b)
What is the mathematical relationship between the maximum kinetic energy of the
photoelectrons and the frequency of the light incident on the metal surface? Define
each term in the equation and its SI unit.
(c)
How could the student best analyse the data to determine a value for Planck’s constant?
p2.66 K
Photoelectrons are emitted by a surface of a certain metal when the surface is illuminated by
both violet light of wavelength 400 nm and green light of wavelength 550 nm but no
photoelectrons are released from the surface by red light of wavelength 715 nm.
(a)
Calculate the frequencies and the photon energies of the three light beams.
(b)
Explain the differences in energies of the electrons released by the violet and green
light.
(c)
Explain why no electrons are released when illuminated by red light.
p2.70 03/14
Heinrich Hertz used a set-up similar to the one shown to
investigate the production and detection of
electromagnetic radiation.
(a)
(b)
(c)
waves.
In the diagram identify the transmitter, receiver,
transmitter, spark gaps, high voltage source.
List the components of the electromagnetic
spectrum
Explain the production and detection of the radio
A glass sheet was placed between the transmitter and receiver.
(d)
Did the radio waves pass through the glass? Explain.
(e)
Were ultraviolet waves blocked when the glass sheet was in place?
(f)
Describe and explain the change in the spark length when the glass sheet was in place.
(g)
How does this relate to the Photoelectric Effect?
p2.72 K
Assess the impact of the discovery of the photoelectric effect of the development of the
quantum model of light.
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p2.90 05/23
Explain how an understanding of blackbody radiation changed the direction of
scientific thinking in the early twentieth century.
p2.95 06/26
Beginning in the late 19th century, observations and experiments on blackbody radiation and
the Photoelectric Effect led physicists to revise their existing model of light.
(a)
What was the existing model for light?
(b)
What was the evidence for this model?
(c)
What model was introduced to explain blackbody radiation and the Photoelectric
Effect?
(d)
Use the above as an example to explain how scientists test, validate and revise models.
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p3.13 08/15
A block of silicon doped with boron is connected to a 10 V battery.
What is the main way in which conduction occurs in the doped
silicon block?
12 V
p3.18 K
Compare the accepted models that are used to describe how an electric current flows in a
metallic conductor at room temperature and a doped semiconductor at room temperature.
p3.22 K
In terms of the band theory explain the essential conditions for a substance to be a
semiconductor.
p3.23 K
Describe how p-type semiconductors are produced.
p3.24 K
Discuss how shortcomings in available communications technology led to an increased
knowledge of properties of materials with particular reference to the invention of the
transistor.
p3.27
undoped
A solar cell can consist of an undoped silicon layer (~
Si
p-Si
1mm thick) placed between very thin (~ 2 nm thick) of
doped silicon.
n-Si
(a) Describe how one of the doped layers can be made.
sunlight
(b) What is the name of the effect that causes the
production of electrons in the undoped layer?
(c) Draw a labelled diagram to show how a potential difference is created across the cell by
the movement of holes and electrons.
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p3.30 02/14
During the early 1950s most transistors were manufactured using germanium.
(a)
Why was germanium used instead of silicon?
(b)
Why is silicon used today instead of germanium?
p3.33 07/14
(a)
Summarize the property of a silicon p-type semiconductor? List a number of possible
doping atoms.
(b)
Summarize the property of a silicon n-type semiconductor? List a number of possible
doping atoms.
p3.39 04/25
An example of a solar cell is
shown. The solar cell is able
to produce a current due to
the photoelectric effect and
the electrical properties of
the n-type and p-type layers.
Use this information to
outline the process by which light shining on the solar cell produces an electric current that
can light up a light globe.
p3.44 07/22 04/23
Explain why solid state devices have largely replaced thermionic devices.
In the past 50 years electrical technology has developed from the widespread use of
thermionic devices to the use of solid state devices and superconductors.
List THREE disadvantages of thermionic devices that led to their replacement.
Outline ONE advantage of using superconductors, with reference to TWO
applications.
p3.52 06/23
(a)
Draw labeled diagrams of the band structures of an insulator, a semiconductor, and a
conductor. With reference to your diagrams, describe the differences in electrical
resistance between insulators, semiconductors and conductors.
(b)
Explain how the addition of trace amounts of certain elements, such as phosphorus,
can change the electrical resistance of semiconductors at a given temperature.
p3.55
Define the terms valance band and conduction band. Draw an energy level diagram for the
semiconductor and diamond.
If a semiconductor has a forbidden band gap of 0.8 eV, what is the maximum wavelength of
electromagnetic radiation that can be used to excite an electron from the valance band to the
conduction band in this material? What part of the electromagnetic spectrum does this
correspond to? Repeat the calculation of diamond, energy gap of 5.0 eV.
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p3.57
Explain why the resistance of a semiconductor decreases as its temperature is increased but
for a metal it increases. Discuss conduction in metals, insulators and semicounductors.
p3.77
Assess the impact of the invention of the transistor on society.
p3.90 05/13
A doped silicon semiconductor has the
following energy-level diagram.
What element was most likely used to dope the
silicon?
p3.92 05/15
A current is passed along a square
semiconductor rod as shown. Half of the
current is carried by electrons and half by
holes. A magnetic field is then applied to
the rod at right angles to its axis. Describes
the movement of the electrons and holes in
the rod when the magnetic field is applied?
p3.95 05/25
A student conducts an experiment using a photoelectric cell. Light is shone through a grid
onto a metal surface. The metal is at earth potential and the grid is at 100 V, so that any
electrons emitted from the surface produce a current in the external circuit. The student
shines light sources of different photon energies onto the metal surface and records the
current flowing for each. The light sources are adjusted so that their intensities are equal. The
results are recorded in the table.
Photon energy (eV)
0.5
0.9
1.2
1.70
1.75
1.90
2.20
2.50
(a)
(b)
(c)
(d)
(e)
Photo-current (μA)
0
0
0.5
2.8
4.0
8.0
9.2
9.4
Plot the graph (X-axis – photon energy).
Draw the straight line of best fit in the region where the photo-current varies greatest
with photon energy.
From the line drawn on your graph, estimate the minimum energy (work function) for
photoelectric emission. What wavelength for the incident em radiation does this
correspond to and what part of the em spectrum?
The experiment is repeated, but the intensities of the light sources are doubled. Predict
the results of this new experiment by drawing a second line on the graph.
Explain the shape of the curves.
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p4.04 07/12 06/11
The Bragg experiment used X-rays to investigate the structure of crystals.
(a)
What property of waves was the basis of their technique?
(b)
What single statement best describes the results of this experiment?
p4.14 K
Magnetic levitation is being investigated and tested for use in a number of areas including
transportation systems.
(a)
What is meant by the term magnetic levitation
(b)
Explain how magnetic levitation occurs in terms of the properties of the substances
involved.
(c)
Describe the benefits and limitations of magnetic levitations as used in maglev trains.
p4.20 07/23
The table shows the critical temperature Tc at which some materials become superconducting.
Year
discovered
(a)
(b)
(c)
Material
Tc (K)
1941
Niobium nitride_
16
1987
YBa2Cu3O7(YBCO)_
92
1993
HgBa2Ca2Cu3O7
133
What is meant by the terms critical temperature and superconducting?
What are the critical temperatures in oC?
What are scientists working in the area of superconductivity trying to achieve?
p4.44 05/24
Explain how superconductivity occurs according to the BCS theory.
p4.49 08/14
The Meissner Effect occurs when a magnet is released above a superconductor that has been
cooled below its critical temperature and the magnet hovers above the superconductor. What
is the best explanation for this?
p4.50 03/23
Compare the model for the conduction of electricity in metals at room
temperature with the model for conduction of electricity in superconductors
below the critical temperature.
p4.60 02/12
Sketch a labeled graph to show how the resistance of a superconducting material changes as
its temperature drops below its critical temperature.
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p4.75 06/21
(a)
Superconductors offer a way of eliminating heating effects in many applications.
Evaluate the usefulness of using superconductors to eliminate energy losses in two
different applications.
(b)
Assess the impact on society and the environment of the potential applications of
superconductors.
p4.78
The diagram shows two pieces of the same
superconducting material above and below its
critical temperature. The pieces are placed in a
strong magnetic field. Complete the diagram to
show the magnetic field in the region of both
pieces. Explain your completed diagram.
superconductors in a magnetic field
above critical
temperature
below critical
temperature
p4.80
Discuss the possible applications of using superconducting technology in computers.
p4.88 03/23
A magnet can hover above a superconducting disk.
(a)
(b)
(c)
(d)
What is meant by a superconductor?
Explain why the magnet is able to hover above the
superconductor.
Name this effect.
List two practical applications of the effect.
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MISCELLANEOUS PROBLEMS
m008 01/25
A student carried out an
experiment on the photoelectric
effect. The frequency of the
incident radiation and the energy
of the photoelectrons were both
determined from
measurements taken during the
experiment.
(a)
(b)
(c)
(d)
(e)
Graph the results.
How could the reliability of the experiment be improved?
The intensity of the incident radiation was tripled. How does it change the graph?
Define the term critical frequency and estimate its value.
Define the term work function and estimate its value.
m013 06/13
The temperature of a metal is reduced. What is the change in its electrical resistance and the
reason for this change?
m020 02/27
Discuss how energy savings can be achieved in each of the two applications of
superconductors.
m045 05/14
An FM radio station transmits at a frequency of 102.8 MHz.
What is the energy, in joules and in eV of each photon emitted by the transmitter?
What is the wavelength of the transmitted signal.
m047 06/27
J. Plücker was the first to observe cathode rays within gas discharge tubes. He inferred that
the rays were a form of electromagnetic radiation.
(a)
Describe a subsequent observation that led other scientists to argue that cathode rays
were charged particles.
(b)
Identify a potential hazard associated with performing experiments with discharge
tube.
(c)
Outline a safe work practice which addresses this hazard.
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m049 05/27
Bubble chambers are used in conjunction with particle accelerators to photographically
record the tracks of fast-moving charged particles. An intense magnetic field is applied at
right angles to the path of the particles to deflect them according to their charge and
momentum. The diagram shows a beam of protons travelling horizontally at 6.00107 m.s-1
and entering a liquid hydrogen bubble chamber in a vertical magnetic field of 1.82 T.
Examination of the photograph taken by the camera, as sketched below, shows that the
protons were deflected along a circular path of radius 0.350 m.
(a)
(b)
(c)
Derive an expression for the momentum of a proton from the forces it experiences
in this experiment.
Calculate the mass of a proton in the bubble chamber.
Calculate the rest mass of a proton found from this experiment.
m050 05/11
The discharge tube shown below
contains a rotating paddle wheel that is
free to move.
The tube’s electrodes are connected to a
high-voltage source.
What does it tell you about cathode rays?
m065
A cathode ray tube and transistor circuits in a conventional television rely on transformers.
What type of transformer are needed for the cathode ray tube and transistor circuits? Explain.
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m072 05/26
The diagram shows two
parallel horizontal metal
plates connected to a DC
source of
electricity. Suspended
between the plates is a
charged particle of mass
9.610-6 kg.
(a) Using conventional
symbols, draw the electric
field between the metal
plates on
the diagram above.
(b) Determine the magnitude of the electric field between the plates.
(c) Determine the sign and magnitude of the charge on the particle if it is suspended
motionless between the plates.
m076
Describe how an investigation can be performed to demonstrate the production and reception
of radio waves.
m080
The electric deflecting plates in a cathode ray tube are 12 mm apart and a potential difference
of 1234 V across them. A beam of positively charged particles moving at 2.67104 m.s-1
travels through the plates undeflected.
(a)
Sketch the experimental setup.
(b)
Calculate the electric field between the plates.
(c)
Calculate the magnetic field strength.
m082 08/21
The work of scientists is influenced by external factors. Do you agree? Justify your answer
with reference to the work of Einstein and Planck.
m088 04/14
The minimum amount of energy needed to eject an electron from a clean aluminum
surface is 8.72 × 10–19 J. What is the work function for aluminum in eV? What is the
maximum wavelength of incident light that can be shone on this aluminum surface in order to
eject electrons? What is the threshold frequency? What part of the electromagnetic spectrum
is the incident radiation?
m095 01/26
Explain the concept of electrons and holes for conduction in semiconductors.
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m111 06/15
When electromagnetic
radiation shines on metals,
photoelectrons may be
emitted. The maximum
kinetic energy of emitted
photoelectrons is plotted
against radiation frequency
for four metals.
Electromagnetic radiation
of wavelength 187 nm
shines upon an unknown
metal and the maximum
kinetic energy of the
photoelectrons is found to
be 2.5 eV. What is the
unknown metal?
m115
The critical temperature of mercury is 4.2 K. What does this mean? Compare how electric
current is conducted through a sample of mercury at 293 K and 3 K. How does this differ
from the conduction in a p type semiconductor.
m120 03/25
When the laser light was shone onto a photocell, no current was detected. The intensity of the
light was increased but still detected no current. Explain this observation.
m200 04/15
The graph shows the intensity–
wavelength relationship of
electromagnetic radiation
emitted from a blackbody cavity.
In 1900, Planck proposed a
mathematical formula that
predicted an intensity–wavelength
relationship consistent with the
experimental data.
The success of this formula
depended on what hypothesis?
Comment on the curve shown.
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m400 01/24
Sir William Bragg and his son Sir Lawrence Bragg shared the Nobel Prize for physics
in 1915 for their work on X-ray diffraction and crystal structure analysis.
(a)
(b)
Describe ways in which an understanding of crystal structure has impacted on science.
Outline the methods of X-ray diffraction used by the Braggs to determine the
structure of crystals.
m550
In a modern cathode ray tube (CRO), the electrons are produced by thermionic emission from
a hot filament forming the cathode. The heating of the filament by a low voltage DC power
source causes electrons to be released from the hot filament with nearly zero kinetic energy.
The electrons are then accelerated away from the filament by a large potential difference
applied between the accelerating voltage plates. This forms a narrow electron beam with the
electrons traveling at the same speed and impact onto the fluorescent screen to produce a
bright spot in the centre.
The accelerating voltage was 5.00 kV. When a magnetic field was applied perpendicularly to
the electron beam, the electrons (cathode rays) followed a circular path with a radius of 5.57
mm. Calculate the strength of the magnetic field.
m680
Hertz used a high voltage source to generate a
spark and realised that when another spark was
produced at a receiving coil, energy must have
been transferred. Early in his experiments Hertz
high
spark
made a chance observation when he could
voltage
gaps
source
increase the strength of the spark in the receiving
coils. Which of the following correctly describes
induction coil
receiver
what Hertz had done that led to this observation?
Comment on each alterative. What was the
transmitter
significance of Hertz’s observation?
(a)
He had shone UV light on the receiving coil.
(b)
He had slightly increased the gap between the terminals of the receiving coil.
(c)
He had placed a glass plate between the transmitter and receiver.
m690
List the properties of the photoelectric effect that could not be explained by classical theory
of electromagnetic waves.
m700
What was the connection between Hertz and the photoelectric effect?
m820 G950
(a)
Estimate the temperature of the surface of the Sun, given that the Sun emits light at a
peak wavelength around 550 nm.
(b)
Which star is hotter, a blue or a red star. Explain
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m950
An electron moving with a velocity of
4.56×106 m.s–1 enters a uniform magnetic field of
strength 3.21×10-2 T at and angle of 42°.
(a)
Describe the path of the electron traveling
through the magnetic field.
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
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







42o e
B
uniform magnetic field out of page
(b)
Calculate the radius of the path followed by
the electron?
m955 03/12
In a first-hand investigation that you performed, you used a
discharge tube containing a Maltese Cross.
What information does the picture tell you?
m960
An electron beam is a special discharge tube is shown.
Show how the electron beam would be deflected by the
magnet. What would happen if the S pole was brought near
the electron beam. Explain your answers.
N
m964 02/11
Describe the difference between an intrinsic semiconductor and an extrinsic semiconductor.
m965 03/26
Describe Einstein’s contributions to Special Relativity and to Quantum Theory and how these
contributions changed the direction of scientific thinking at the beginning of the 1900s.
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m970
The flowchart represents a model of
the scientific method used to show the
relationship between theory and the
evidence supporting it.
Analyse Einstein’s Theory of the
Photoelectric Effect and the evidence
supporting it as an application of this
model of scientific method.
m990
Max Planck and Albert Einstein were both personally affected by the years before, during
and after WWII. They also had strong views about the role science in the period before the
war. Discuss Planck’s and Einstein’s differing views about whether scientific research is
removed from social and political issues.
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