Year 11 Yearly Notes - Physics

Year 11 Physics Notes
Unit 1.1: The Wave Model
The Wave Model
 The wavefront can either be the crest or trough and is perpendicular to the direction of the
wave's velocity.
 Two waves are in phase if at an instant they have the same displacement and velocity
 The amplitude is the maximum displacement from the undisturbed state.
 The frequency is the no. of waves that passed a fixed point per second.
 The velocity of a wave is how fast the wave transfers energy away.
The period is the time it takes a single wave to pass a fixed point
Unit 1.2: Waves Carry Energy
When a wave travels through a medium, the medium does not move forward with the
disturbance, the particles simply move up and down perpendicular to the wave direction.
It is simply a transfer of energy.
Waves may travel in one, two or three dimensions e.g. slinky or rope waves are 1D, ripple
waves are 2D and sound waves are 3D(radiates in a sphere from the origin)
Unit 1.3: Types of Waves
Waves are categorised according to how they transfer energy:
 Mechanical waves involve transfer of energy through a material by the motion of particles of
the medium. The particles oscillate or vibrate but return to the same place as they were
 Electromagnetic waves don't require a medium to travel through.
Mechanical waves are classified as transverse or longitudinal:
 In transverse waves, particles of the medium vibrate perpendicular to the direction of wave
 In longitudinal waves, the particles of the medium oscillate in the same direction of the wave
Electromagnetic waves are all transverse waves because the alternating electrical and magnetic
fields are perpendicular to each other and the wave propagation.
 EM waves travel at the speed of light and can be reflected, refracted and carry information as
 They are self-propagating, that is the magnetic field produced induces an electric field and vice
versa etc.
 EM waves can travel immense distances and create an electrical response in the medium they
come in contact with
Mobile Phones
 Mobile phones have microphones that change sound waves into electrical signals.
 These electrical signals are digitised (converted into 1s and 0s) and transmitted as radio
waves to base stations.
 The base station accepts and transmits the radio signals from antennae in three adjacent
hexagonal areas called cells.
 Each base station is connected to a switching centre by cable network carrying signals as
electrical impulses produced by radio waves interacting with the aerial.
 If the telephone call is between a mobile and a fixed telephone, the signal is transferred
through copper-wire networks as electrical impulses and possibly via optical fibre
networks if it is a long distance away to a closer switching centre. The receiving telephone
will then convert it back into sound energy.
 If the call is between two mobile phones, the signal is transferred to a closer switching
centre and fed to a base station which broadcasts the electrical impulses as radio waves.
The radio signal is converted back into electrical impulses and into sound.
Unit 2.1: Sound - Vibrations in a Medium
All sound waves are vibrations in a medium that result in pressure variations within that
The higher the volume of the sound, the greater the amplitude and vice versa.
The higher the pitch of the sound, the faster the rate of vibration of the object (frequency)
and vice versa.
In the zones of high pressure, the particles of the medium are pushed closer together, this
is a compression.
In the zones of low pressure, the particles of the medium are spread further apart, this is a
Unit 2.4: Echoes - Reflections of Sound
An echo is a repeated sound created by the reflection of sound waves from a surface.
When an echo bounces back from a solid surface, such as a cliff face or a brick wall, you
don’t hear the full sound.
If you are close to the reflecting surface, you probably won't detect an echo as the original
sound drowns it out.
If you are a significant distance away from the reflecting surface, you will hear more of the
original sound bounce back.
Sonar technology works by emitting short-wavelength, high frequency waves that bounce
back from objects. The time taken to return to the source can be used to determine the
distance from the object.
Unit 2.5: Sound and the Principle of Superposition
Sound waves from separate sources may interfere with each other to produce a sound of
higher or lower amplitude by adding the amplitudes together.
If two waves are in phase the amplitudes are added to make a louder sound. This is called
If two waves with the same amplitude are out of phase by 180 degrees, they cancel out
resulting in no sound. This is called annulment.
If two waves are out of phase, the amplitude will be less than either of the original waves.
Conversely, if they are in phase the amplitude will be greater than either of the original waves.
Some uses of this phenomenon include:
o Production of sound waves that are out of phase by 180 to reduce sound emitted by
heavy machines
o Noise cancelling technology in headphones.
Interference of waves can also produce waves with different frequencies.
As waves drift out of phase, the resulting amplitude will decrease reaching zero and then
increase again as they drift back in phase.
Beats refer to the variation in volume of a sound that occurs when two sounds of slightly
different frequencies occur together.
Unit 3.1: The Waves of the Electromagnetic Spectrum
The electromagnetic spectrum is the full range of wavelengths of all EM waves:
 Radio waves
o Wavelengths 10cm - 1000m
o Frequencies are categorized as AM, FM, VHF and UHF
 Microwaves
o Wavelengths 1mm - 30cm
o Transmission can travel distances of up to 100km but there must be a direct line of sight
from transmitter to receiver as they travel in straight lines
 Infra-red radiation
o Wavelengths 700nm - 1mm
o Detected by electronic detectors
 Visible light
o Wavelength 400 - 700nm
 Ultraviolet
o Wavelength 10 - 400nm
o Small doses encourages production of vitamin D
o Large doses lead to cell and tissue damage and develop skin cancer, most harmful
radiation is absorbed by the atmosphere
o Detected by UV detectors
 X-rays
o Wavelength 0.01 - 10nm
o Used for medical examination of dense parts of the body
o Can be detected by photographic film
 Gamma rays
o Wavelengths less than 0.01nm
o Treatment of some cancers
o Detected with a Geiger counter
Unit 3.2: Atmospheric Filtering of Electromagnetic Waves
The Earth’s atmosphere and ionosphere absorb most of the incoming electromagnetic
radiation from space except for visible light and some high-frequency radio waves in the
microwave region.
The ionosphere is a layer of gas that is ionised by losing or gaining electrons between 50km 500km above Earth
The ionosphere consists of 3 layers: D, E and F
o D layer: 50- 80km, hard x-ray radiation with short wavelengths/ high frequency and most
infra-red radiation absorbed
o E layer: 80 -105km, soft x-rays with long wavelengths, gamma rays, UV rays are
F layer: 145- 300km/600 km at night, extreme ultraviolet radiation with short
wavelengths absorbed
Some solar activities such as solar flares release large bursts of energy that increase ionisation
and change the degree of reflection and absorption.
The Communication Spectrum
 The government restricts the range of frequencies and limits the bandwidth over which certain
communication devices can operate. This is done to:
o Avoid interferences
o Provide equity for users because the communication industry is very competitive
o Enable communications for the safety infrastructure
o Allow development of new technologies that require spectrum bandwidth
Unit 3.3: Electromagnetic Radiation and the Inverse Square Law
Communication technology that uses electromagnetic waves is able to travel long
distances but signal strength decreases. This is known as attenuation where there is a
falloff in energy as a wave passes through a medium.
To reduce attenuation effects, electromagnetic waves are released with very large
strength or the signals are amplified at repeaters or booster stations.
Very weak signals may be collected by a receiver that covers a large area and focuses the
signal to increase its strength e.g. satellite dishes
The inverse square law states that the intensity of electromagnetic radiation is inversely
proportional to the square of the distance from the source of the radiation:
Light intensity (illuminance) is measured in units called lux (lx).
e.g. if you were one metre from a light source where the light intensity was 16 000 lx,
Unit 3.4: Modulation of Waves to Transmit Information
A wave that carries exactly the same amount of energy continuously does not carry
 There are two simple ways to vary a wave to add information to it. You either vary the
frequency (and hence wavelength and energy) of the wave or you vary the amplitude (and
hence energy) of the wave.
 The process of adding the signal information to an electromagnetic wave is called modulation.
 The modulated wave that makes up the signal must then be converted back into information
you can use. That process is called demodulation.
Modulating a Radio Wave
 A radio-wave signal occupies a bandwidth of frequencies. This means that the transmitted
wave is using a number of frequencies forming a band in the spectrum.
 In the middle of that bandwidth is the carrier wave. The carrier wave does not carry any
information and acts as the central frequency to which the receiver is tuned.
 The message signal is added to that carrier wave. This is done by superposition of a signal
wave onto the carrier wave.
 The signal is added to an AM carrier-wave radio signal by changing the amplitude of the wave
but the frequency remains constant.
 The variation in the amplitude of the wave is decoded by a radio receive which is amplified
and converted to the sound signal you hear.
 A frequency-modulated (FM) radio transmission means that the signal part of the wave has
been added to the carrier wave to vary the frequency of the wave.
 A limiting circuit in the radio receiver removes any amplitude variations that occur during
transmission of the radio signal and keeps the amplitude of the received wave near constant.
 The signal is converted back into sound by a discriminator circuit.
 The effects of ‘static’ are reduced in FM radio broadcasts because the FM radio signal is not
dependent on the strength (amplitude) of the signal received, but rather relies on the
frequency. It is much harder to change the frequency of a wave by interference.
 AM radio requires a much smaller bandwidth of frequencies for transmission allowing a larger
number of transmissions.
Modulation of Microwaves
 Microwaves are preferred over longer wavelength radio waves for mobile telephone systems
o The electromagnetic spectrum is limited and the microwave bandwidth has the capacity
o Microwaves don't spread out as much allowing more energy to reach the receivers
o The large range of frequencies in the microwave transmission range allows a large
number of signals to be transmitted at once i.e. up to 20000 telephone calls can be
transmitted at once
Modulation of Visible Light
 Light modulation is also used to carry signals e.g. laser light transmission but is very
susceptible to interference.
 As such, long distance communication via light is accomplished along fibre-optic cables
 Radar works by sending out evenly spaced pulses of radio-wave energy of a certain
 Electrons move in an alternating current that has a controlled frequency.
 The up and down movement creates pulses, which reflect back when the they strike an object
creating an echo for the radar antenna to detect
 A computer receives the AC information about where the echo is coming from, whether the
wavelength has been altered and how long each pulse takes to return
 A visible-light track of the moving object is generated on the radar display
 The radar uses an accurate, high-speed clock to process the radio waves travelling at the
speed of light and measure the speed of the object.
 This is done by looking at the Doppler shift or change in wavelength of the radio waves:
o If the object is moving away from the source the wavelengths will be lengthened as a
result of collision and reflection
o If the object is moving towards the source, the reflected wavelengths are shorter.
Unit 4.1: The Law of Reflection
The Law of Reflection states that the angle of the incoming, or
incident, wave in relation to a line perpendicular to the reflecting
surface (normal) is equal to the angle the reflected wave will make
with the normal.
More simply, the angle of incidence = the angle of reflection.
The normal is the line that is perpendicular to the reflecting surface
at the point where the ray hits it
When the waves are reflected from a flat surface, the reflection is
regular. When the reflection is from a bumpy or irregular surface, it
is a diffuse reflection.
If a surface is some distance away from a light source, the light rays
that reach the surface are considered to be parallel.
When the surface is irregular, each of the parallel incident rays that hits the surface does so at
a different angle of incidence and the reflected rays are no longer parallel.
To the observers, the reflected rays will not be as intense as the incident rays because the
reflection is diffused so not as many rays reach the person whereas parallel rays will reach the
observers in larger numbers.
The Law of Reflection allows you to explain the properties of the image formed by a reflection.
Those properties include:
• the size of the image
• the nature of the image
• the apparent location of the image
• the orientation of the image compared to the original object.
A real image is one that can be projected onto a screen.
A virtual image can be seen but cannot be projected onto a screen.
When light is reflected from the surface of a material with a lower index of refraction, there is
no phase shift.
 The focus is the point where all rays from a converging lens or mirror are concentrated.
Reflection from Curved Mirrors
 To accurately describe how rays are reflected and how curved mirrors form images, we use
certain terms. These include:
• the sphere centre, C,
• the pole of the mirror, P, (the central point of the mirror that would lie on the diameter of
the sphere.)
• the principal axis, which is the radius of the sphere (from which the mirror may have been
made) that passes through C and P.
 When light rays strike a concave (or converging), spherical-mirror
surface in a direction that is parallel with the principal axis, they
are reflected so that they converge to a single point called the
 The focus is at a distance equal to half the distance of the radius of
the sphere from which the mirror could have been made. For both
concave and convex spherical mirrors the focus is halfway between
P & C.
 When light is reflected by a convex (or diverging) mirror, any
incident rays hitting the mirror (with a direction parallel to the
principal axis) are reflected and diverge as though they originate at
a point behind the mirror.
Unit 4.2: Applications of Reflection
The Astronomical Telescope
 In a Newtonian telescope the main light-collecting mirror is either a concave spherical mirror
or a parabolic mirror.
The Cassegrain telescope had a hole cut in the concave main mirror. The reflected light from
the main mirror was reflected back to the eye piece by a small convex or hyperbolic mirror.
This meant the telescope had a shorter barrel length and the image was viewed in the
direction of the object rather than perpendicular to it.
The telescopes are coated with aluminium and are front-silvered concave parabolic mirrors.
Parabolic mirrors have the advantage over spherical mirrors of being able to eliminate
spherical aberration which is the distortion seen when we view things with a single convexlens system such as a magnifying glass.
Spherical Aberration is where the image seen at the centre is clear and focused, but near the
edge of the glass the same object appears distorted and out of focus.
Other Applications
 Torches and driving lights often use parabolic, concave-mirror reflectors where the filament
may be adjustable. If the filament is at the focus it will create a spot beam whereas if the
filament is beyond or before the focus it will create a flood beam.
Radio Waves
 There are three types of radio waves used for communication technologies: sky waves, space
waves and surface waves.
 Space waves penetrate the ionosphere and are used to communicate with satellites and the
International Space Station in a direct line of sight manner.
 Sky waves bounce off the ionosphere due to high frequencies and low wavelengths. The radio
waves travel even further at night due to the ionosphere rising at night.
Unit 4.3: Refraction
Refraction is the where waves bend as they pass from one medium or depth to another.
Refraction of a ray slower in medium 1 than medium 2 bends away from the normal.
Unit 4.4: Refractive Index and Snell's Law
Snells Law:
If a ray passes from a vacuum to another material of fixed composition and density, the
degree of bending that occurs at the interface is a constant. This constant is given the
symbol n and is known as the absolute refractive index.
All refractive indexes are measured with respect to a vacuum. A vacuum by definition has
an absolute refractive index of 1.0000 for the electromagnetic spectrum.
The absolute refractive index of any transparent material is also a ratio, of how much an
electromagnetic wave slows down at the interface between a vacuum and that material
such that:
The frequency of the waves does not change as they speed up or slow down, so it is the
wavelength of the wave that changes. Hence,
Furthermore, the refractive index can be used to determine what will happen to a wave as
it passes the interface:
Unit 4.5: Total Internal Reflection
Total internal reflection may occur when a ray of light attempts to cross into a low-refractiveindex medium from a high-refractive-index medium
A small change in the angle of incidence can cause a larger change in the angle of refraction. It
is possible for an angle of incidence to reach a critical angle where the ray can’t exit the higher
refractive-index material.
The ray is refracted so much that it is bent to 90° from the normal at the interface and travels
along the interface.
The critical angle is the angle of incidence where total internal reflection prevents the ray from
escaping from a high density medium to a low density medium
If the critical angle of a ray at the interface of two substances is exceeded, the interface will
act as a mirror and total internal reflection of light rays occurs obeying the Law of Reflection.
Calculating the Critical Angle
Unit 4.6: Optical Fibres and Total Internal Reflection
Optical fibres are made from thin, cylindrical strands of ultra-high purity glass
These optical fibres are made so that they have a central, high-refractive-index region
called a core.
Their outer region, called the cladding, is made from a lower refractive-index glass.
The EM waves are totally internally reflected at the interface, and continually moves
forward through the optical fibre.
To allow this transfer of trapped light to be faster and more efficient, the diameter of the
core is made around 10 μm (nanometres).
Optical fibres are used for communication to carry signals at high speed and medicine to
view organs through endoscopes.
Optical fibres allow transmission of light where straight line transmission of the light is not
possible as they are quite flexible.
Unit 4.7: Digital Communication Systems
Digital signals are based on a binary code of 1s and 0s.
Advantages of digital communication include:
o Enhanced security
o Ability to withstand interference and superposition and still preserver the signal
A sound, picture or data is initially generated as an analogue signal that is frequency- or
The quantisation process is then applied to the analogue signal where the analogue wave
shape is converted into a code that represents a set of numbers. These numbers can be
represented in a binary code of 1s and 0s
In 8-bit processing, the signal is represented as a series of numbers from 0 to 7 that can be
represented using some combination of three 0s or 1s. The amplitude of an analogue wave at
a particular time interval is scaled and converted to a number on a scale from 0 to 7 for 8-bit
processing. This is called sampling.
The sampled information is converted by a digital encoding device to a sequence of a
combination of three 0s and 1s.
To increase the accuracy of the wave reconstruction to the original analogue signal, two things
can be done.
o More samples can be taken at closer time intervals.
o The number of divisions on the vertical scale can be increased by making the processing
16-bit, 32-bit or 64-bit.
Types of Communication Data
Types of communication data stored or transmitted in digital form:
 CD technology
 The internet
 DVD technology
Case Study: Compact Disc
 The compact disc is a plastic, metal-coated disc that stores information digitally.
 The information is stored as a series of pits on the surface of the CD representing 1s on a track
spiralling outwards from the centre
 Where there is no pit, it represents the 0s. These 1s and 0s are ready by a laser and used to
reconstruct the original signal.
 Recording a CD involves a microphone that translates sound waves into analogue electric
 An encoder divides the wave signals into 44100 segments each representing a second of sound
and converts them into digital code based on the amplitude of the analogue signal
 A single pulsing laser uses this code as an on/off template to cut a spiral track of microscopic
 When playing a CD, a laser beam shines on the metal coating of the disc which reflects the
light back
 The intensity of the reflected light varies depending on whether there is or isn't a pit which is
translated into an electrical signal and decoded by circuits to produce sound waves
Unit 5.1: Galvani and Volta
Luigi Galvani
 Luigi Galvani(1737-1798) was an Italian physician and physicist
 In 1772, Galvani was experimenting on a frog's legs using an electrostatic machine (device for
making sparks). He discovered that the frog's legs would contract if a scalpel touched it when
the machine was working.
 In 1786, he observed that frog's legs would contract if two different metals attached to the leg
muscle and the spinal cord touched
 Animal electricity was the term used for the form of electricity believed to be generated by
animal tissues.
 Galvani thought that the muscle in the frog’s leg produced a positive charge in one area of the
muscle and a negative charge in another area. When the two areas were connected by a
metal, a discharge took place which caused the muscle to contract.
Alessandro Volta
 Alessandro Volta (1745-1827) was an Italian physicist.
 Volta initially carried out experiments to confirm Galvani's theories and accepted them.
Galvani's theory did not however explain why two different metals were needed.
 In Volta's view, the source of electricity was generated from the contact of the two metals,
one became positively charged and the other became negatively charged. He believed there
was no animal electricity, the frog's legs just acted as a detector of the electricity.
 Volta tested this using a voltaic pile, a battery of zinc and brass discs with cardboard
moistened in salt solution in between. Each time the conductors at each end were connected,
sparks were continuously produced disproving Galvani's animal theory.
Was Volta Right?
 Humphrey Davy proved that the source of electricity produced by Volta's experiment was
actually chemical reactions involving the salt solution and the two metals.
 Volta was right that when two different metals came into contact, one became positively
charged and one became negatively charged inducing a small pulse of current.
Unit 5.2: People's Use of Energy Sources Before Electrical Energy
Chemical energy of wood
converted into heat
First energy source used by
Used to produce fire
Social Impacts
Fire helped keep fierce animals at
Food could be cooked
Points of sticks could be hardened
for weapons
Humans able to live in colder
Source of mechanical energy
Used for farming and transport
More food and people
Better transport
Wind and water
Windmills/water wheels
Wind used for boats
Became main fuel source due to
high energy
Industrial revolution
Coal gas
Heat and lighting
Social activity at night
Unit 5.3: People's Use of Electrical Energy
Michael Faraday discovered electromagnetic induction which led to large scale energy
production through generators driven by steam from heating water through burning fuel,
nuclear power or hydro-electric power.
Distribution of Electrical Energy
 Power stations generate electricity at around 10 000 volts and 10 000 amps.
 Transformers step up the voltage and lower the current for long range transmission through
power lines to make transportation more efficient
 Power stations can be connected together in a grid so that stations with low demand for
energy at a time can assist the one experiencing high demand
 Remote places that aren't connected to a power station use small generators where an
internal combustion engine rotates a coil, and arrays of small solar cells and wind turbines.
Chapter 6: Electric Charges, Fields and Currents
Unit 6.1: Electric Charge
Electric charge is a property of electrons and protons by which they exert electric forces on
one another.
 The SI unit of electric charge is the Coulomb which is approximately equal to 6.25 x 10 18
 The charge on one electron/proton is approximately ±1.60 x 10-19C.
 A body may gain electrons (excess of electrons) or lose electrons (deficiency of electrons). The
resulting charge on a body due to excess or deficiency of electrons is called electrostatic
Conductors and Insulators
 A conductor is a material that contains charge carriers, that is, particles that are free to move
through a material.
An insulator is a material that does not contain charge carriers.
A body is insulated if it is not earthed, where the electrostatic charge is distributed on the
surface of the conductor
 A body is earthed if it is connected to the Earth by a conducting path where the electrons will
move to or from the Earth to neutralise the conductor.
 When two bodies made of different materials are rubbed together a small number of
electrons will be transferred creating a deficiency of electrons on one body and an excess on
the other.
 If a charged conductor is brought into contact with an uncharged conductor, the charge will be
shared between the two conductors i.e. the uncharged conductor will be charged by contact.
 When a positively charged body is brought near an uncharged conductor the electrons will
move to the area closest to the charged body resulting in an excess of electrons on one side
and a deficiency on the opposite side.
 These charges are called induced charges(charges produced in a body when another charged
body is near it).
 Induction is the production of induced charges.
Induction charges will usually disappear when the charged body is removed but in some cases
it may be permanent:
Electric charge is always conserved:
o When two neutral bodies are charged by friction, the amount of positive charge
produced on one body is equal to the amount of negative charge produced on the other
o When two charged conductors are brought into contact, there is a redistribution of
charge between the bodies but the total amount of charge remains the same.
Unit 6.2: Electric Fields
An electric field is a region where an electric charge experiences a force. The charge itself
will not experience any force from its electric field, only other charges placed in its field.
The direction of the electric field at a point is defined as the direction of the force that acts
on a positive electric
charge placed at the point.
The magnitude of the electric field strength at a point is the magnitude of the force per
unit charge at the point:
The lines of electric field are lines drawn on a diagram to represent the direction and
magnitude of an electric field(the closer together the lines, the stronger the electric field).
A uniform electric field is an electric field with the same magnitude and direction at all
When there is more than one point charge producing an electric field, the fields from the
individual charges combine to produce a single resultant field.
At some points, the two charges will cancel each other out called null points where the
electric field strength is 0.
In drawing lines of electric fields:
o lines start on positive charges and end on negative charges
o lines never cross (the field cannot have two directions at a point)
o the greater the charge, the greater the number of lines starting or ending on it
o eual charges have equal numbers of lines starting or ending on them.
Unit 6.3: Electric Potential Energy
Electric potential energy is the potential energy of an electric charge in an electric field.
o The electric potential energy of a charge in an electric field is similar to the gravitational
potential energy of a mass in a gravitational field.
o The free movement of a charge in an electric field is similar to a mass falling in the
Earth’s gravitational field.
o Moving a positive charge in the opposite direction to an electric field is similar to raising
a mass in a gravitational field.
 When a positive charge moves in the direction of an electric field, its electric potential energy
 When it moves in the opposite direction to an electric field, its electric potential energy
 When a negative charge moves in the opposite direction to an electric field, its electric
potential energy decreases.
 When a negative charge moves in the direction of an electric field, its electric potential energy
Potential Difference
 The potential difference between two points in an electric field is the change in electric
potential energy per coulomb of charge that moves between the points.
Unit 6.4: Electric Currents
Electric current is the rate at which charge flows under the influence of an electric field.
The SI unit of electric current is the ampere (A) which is the amount of current flowing when a
net charge of one coulomb flows through a cross-section of a conductor in one second hence
coulomb per second(Cs-1).
Free electrons are electrons in a metal that are detached from their atoms and are free to
move through the metal. A metal conducts an electric current by the movement of the free
If there is an electric field in a metal, the free electrons will experience a force in the opposite
direction to the field. This is called electron drift which is superimposed on the much faster
random motion of electrons.
As the free electrons drift, they continually collide with the positive ions in the metal lattice
transferring their kinetic energy to heat energy in the form of vibrations. Thus, when an
electrical current flows through a metal, electric potential energy is transformed into heat
Conductors and Resistors
 Conductors for electric circuits are made so that there is negligible conversion of electric
potential energy into heat energy.
 Resistors are conductors where the electric potential energy of a current is converted into
heat energy.
 The potential difference/voltage across a resistor is the number of joules of electric potential
energy dissipated by each coulomb of charge that passes through.
Power Supply
 The power supply is a source of electric potential energy for resistors to transform into heat
energy e.g. batteries convert chemical energy to EPE and photoelectric cells convert light
energy to EPE
 A power supply has positive charges and negative charges separated into a positively charged
terminal and a negatively charged terminal.
 When a conducting path joins the two terminals, an electric field is formed which exerts forces
on the free electrons of the conducting metal causing them to drift towards the positive
terminal creating an electric current.
 The potential difference across a power supply is the number of joules of electric potential
energy given to each coulomb of charge that passes through.
 It was thought in the past that a current was a flow of positive charges to the negative
terminal. This is known as the conventional current direction and is always used in circuit
 An ammeter is an instrument used to measure current by connecting it into a circuit in series.
o If the current is measured on each side of a resistor, it is found to have the same value
as the current does not get ‘used up’. What gets used up is electric potential energy.
A voltmeter is an instrument used to measure the potential difference across a component by
connecting it into a circuit in parallel.
o The potential difference across a wire/conductor should be zero because there is
negligible conversion of EPE to heat energy in a conductor.
The potential difference across the power supply is equal to the potential difference
across a resistor because the EPE dissipated in a resistor should be equal to the EPE
generated by the power supply.
 The resistance of a resistor is the potential difference across the resistor divided by the current
passing through:
The resistance of a conductor is a result of collisions between the free electrons and the lattice
of positive ions.
The greater the number of collisions, the greater the resistance hence,
Factors affecting resistance are:
o Length
Area of cross-section
 The smaller the area of cross-section of the wire, the greater the chance of a
collision of a free
 Different materials will have different resistances e.g. silver has a resistance of 0.94
x10-2 so it is a good conductor whereas nichrome has a resistance of 58 x10-2 so it
is a good resistor
 When the temperature of a conductor is increased, the ions in the lattice vibrate
with greater amplitude. This increases the chance of a collision between a free
electron and therefore increases its resistance.
Chapter 7: The Household Electricity Supply
Unit 7.2: Using Electricity Safely in the Home
The electricity supply in a home is delivered through overhead or underground cables to a
switchboard into a fuse box or circuit breaker box where it is divided into a number of parallel
circuits throughout the home.
The alternating voltage is delivered by two wires called the neutral and the active/hot wire.
o The neutral wire is maintained at earth potential by being connected to the earth at the
power station.
o The active wire varies between +340V and -340V with respect to the neutral wire.
The AC supply has the same heating effect as a 240V DC supply so it is called a 240V AC supply.
Electric Shock
 Electrocution is caused by an electric current passing through the body and causing a
disturbance of the nervous and muscular systems.
 Electric shocks most commonly occur when a person comes into contact with the active wire
while in contact with the ground causing muscle contractions.
Fibrillation is a condition in which the heart stops beating regularly and oscillates rapidly.
An overloaded circuit carries a current higher than the maximum safe value for which the
circuit was designed.
o Electrical fires can occur if a circuit is overloaded and becomes hot enough to start a fire.
 A short circuit is where an active wire comes in contact with the neutral wire or is earthed.
o This creates a circuit with very little resistance leading to a very high current and
sufficient heat to start a fire.
Safety Devices
 All household electrical wiring must be covered with a PVC insulator and many appliances
even have double insulation in case the inner insulation fails.
 Fuses are high resistance wires that are connected in series with the active wire to prevent
overloading. The fuse will generate more heat as it has a higher resistance than the rest of the
circuit causing it to melt if the current exceeds the limit inside an insulated tube.
Circuit breakers use electromagnets to mechanically break the circuit when the current
exceeds the maximum value and can be re-used unlike fuses.
Earth wires are wires coming from the earth connected to the neutral wire and each power
o When an appliance is plugged in the earth wire is connected to the casing of the
appliance so that if the active wire comes in contact with the casing of the appliance, a
large current will flow through the earth wire to the earth and trigger the fuse or circuit
Residual current devices detect any leakage of current to the earth either through your body
or some other conductor and switch off the current if so.
A typical household wiring system:
o Each circuit is connected in parallel to give 240V to each
o Switches are placed on the active wire to prevent electric shocks.
Chapter 8: Using Electricity in the Home
Unit 8.1: Power in Electric Circuits
Power is the rate at which energy is transformed from one form to another measured in Js1
or watts.
When resistors are connected in series:
o The same current flows through all the resistors and power supply
o The voltage gain across the power supply equals the sum of voltage drops across the
o The greater the resistance of a resistor, the greater the voltage drop and the greater
the power dissipated
o The power generated by the power supply equals the sum of the powers dissipated
in the resistors
When resistors are connected in parallel:
o The current through the power supply equals the sum of currents through the
o The voltage drop across each resistor is the same and is equal to the voltage rise in
the power supply
The greater the resistance of a resistor, the smaller the current passing through.
The greater the resistance, the smaller the power dissipated in it.
The power generated by the power supply equals the sum of the powers dissipated
in the resistors
A kilowatt-hour (kW-h) is defined as the amount of energy used by a 1 kW device in 1
Unit 8.2: Magnetism
A pair of equal and opposite magnetic poles is called a magnetic dipole.
If a magnet is broken in two in an attempt to separate the north and south poles, new south
and north poles appear on both pieces.
The magnetic field is a force field surrounding a magnetic pole that exerts forces on other
magnetic poles placed in the field.
The direction of a magnetic field is the direction of the force on a very small magnetic north
pole placed in the field.
A compass consists of a magnet suspended so that it is free to rotate until the north pole of
the compass is pointing in the direction of the magnetic field.
Magnetic Field Lines
 Magnetic field lines start at north poles and end at south poles.
 The direction of magnetic field lines shows the direction of the magnetic field.
 The spacing of the field lines shows the strength of the magnetic field, closer = stronger field.
Unit 8.3: Magnetic Fields and Electric Currents
Christian Oersted discovered that a nearby compass needle changed direction while
demonstrating the flow of an electric current.
The magnetic field lines surrounding a long, straight wire carrying a current are concentric
circles around the conductor.
Right hand grip rule:
o Grip the wire with the right hand, with the thumb pointing in the direction of the
conventional current and the fingers will curl around the wire in the direction of the
magnetic field.
Drawing a diagram of a wire is done by imagining the wire is perpendicular to the page going
in through it or out of it.
 If a straight wire carrying a current is bent into a loop, the magnetic field is as shown in figure
 The magnetic field lines come out at one side of the loop, which is therefore like the north
pole of a magnet.
 The right-hand grip rule, applied to a section of the loop, gives the direction of the magnetic
A solenoid is a wire that has been wound into a closely packed helix (corkscrew shape).
When a current passes through a solenoid, magnetic fields are produced both inside and
outside the solenoid.
The magnetic field outside the solenoid is similar to the magnetic field surrounding a bar
For the solenoid, however, the lines of magnetic field do not stop at the ends of the solenoid
but pass through the inside as parallel lines forming closed loops.
The end where the lines of magnetic field emerge from the solenoid is the North Pole.
To determine which end of a solenoid is the north pole:
o Grip the solenoid with the right hand, with the fingers pointing in the direction of the
conventional current around the solenoid.
Observe the solenoid end on. If the direction of the conventional current is anticlockwise, the end is a north pole; if the conventional current is clockwise, the end is a
south pole.
 When magnetic material is placed in a magnetic field it becomes magnetised.
Temporary magnets will become magnetised when placed in a magnetic field and lose it when
removed e.g. soft iron.
Permanent magnets become magnetised slowly but retain their magnetism when removed
e.g. hard iron.
Placing hard iron inside a solenoid will form a permanent magnet over time.
Placing soft iron inside a solenoid will form an electromagnet, when a current is applied the
soft iron magnetises forming a much stronger magnetic field than the solenoid.
Magnetic tape consists of a coating of microscopic particles of magnetic material suspended
on a plastic backing such as acetate.
During recording, an alternating current, derived from sound waves, is passed through the coil
of the recording head producing a varying magnetic field in the air gap between the poles that
magnetises the magnetic particles on the tape.
Chapter 9: Describing Movement
Unit 9.1: Distance and Displacement
Distance is a measure of the total length of the path taken during the change in position of
an object. It is a scalar quantity.
o A scalar quantity specifies size/magnitude but not direction.
Displacement is a measure of the change in position of an object. It is a vector quantity.
o A vector quantity specifies size/magnitude and direction.
Unit 9.2: Speed and Velocity
Speed is the measure of the rate at which an object moves over a distance. It is a scalar
Velocity is a measure of the time rate of displacement or the time rate of change in
position. It is a vector quantity.
The velocity of an object measured by a moving observer is referred to as the relative
The relative velocity is the difference between the velocity of the object relative to the
ground and the velocity of the observer relative to the ground.
Neither the average speed nor the average velocity provides information about movement
at any particular instant of time.
Instantaneous speed is the speed at a particular instant of time and instantaneous velocity
is the velocity at a particular instant of time.
If an object moves with a constant velocity during a time interval, its instantaneous
velocity throughout the interval is the same as its average velocity.
Unit 9.3: Acceleration
The rate at which an object changes its velocity is called its
acceleration. It is a vector quantity.
The direction of the acceleration of an object is the same as the
direction of its change in velocity.
To subtract u from v, one vector can be subtracted from
another by adding it’s negative.
Constant Acceleration
 When acceleration is constant, the motion of an object can be described as:
Chapter 10: Force and Newton's Laws of Motion
Unit 10.1: Analysing Forces
A force is a push or pull vector quantity measure in Newtons.
Weight is the force applied to an object due to gravitational attraction.
The gravitational field strength, which is usually given the symbol g, is defined as the force
of gravity on a unit of mass and is equal to 9.8ms-2 on Earth.
The normal reaction is a force that acts perpendicular to a surface as a result of an object
applying a force to the surface.
The vector sum of the forces acting on an object is called the net force.
Unit 10.2: Forces in and out of Balance
Newton's First Law of Motion
 Every object continues in its state of rest or uniform motion unless made to change by a nonzero net force.
 When a non-zero net force acts on an object, it accelerates in the direction of the net force.
The acceleration can be a change in speed, direction or both.
Unit 10.3: Newton's First Law and Inertia
Newton's First Law of Motion is also known as the Law of Inertia, where inertia is the
tendency of an object to resist a change in its motion.
Inertia is not a force, it is a property of all objects that is entirely dependent on an object's
Unit 10.4: Newton's Second Law of Motion
It can be said that the acceleration of an object is:
o Proportional to the net force(acceleration increases when increased force is applied)
o Inversely proportional to the mass(lighter objects show greater velocity changes
than heavy objects)
Unit 10.5: Newton's Third Law of Motion
For every action there is an equal and opposite reaction e.g.
o When you swim, you push the water backwards with your hands, arms and legs. The
water pushes in the opposite direction, propelling you forwards.
o In order to walk or run, you push your feet backwards and down on the ground. The
ground pushes in the opposite direction, pushing forwards and up on your feet.
o The forward driving force on the wheels of a car is the result of a push back on the road
by the wheels.
o A jet or a propeller-driven plane is thrust forwards by air. The jet engines or propellers
are designed to push air backwards with a very large force. The air pushes forward on
the plane with an equally large force.
Newton's Laws of motion can be applied to multiple bodies in a system individually or as a
Circular Motion
 Centripetal acceleration is the acceleration of an object travelling in a circular path with
constant speed. It is directed towards the centre of the circle.
 The acceleration of an object travelling at a constant speed in circular motion of radius r can
be expressed as:
Hence, the magnitude of the net force on an object travelling in a circular path called the
centripetal force can be expressed as:
Chapter 11: Mechanical Interactions
Unit 11.1: The Concept of Energy
Energy is the capacity to do work. It is a scalar quantity.
Work is done when an object moves in the direction of a force applied, it is a scalar
quantity. The amount of work done is the product of the magnitude of the force and the
displacement of the object in the direction of the force:
Unit 11.2: Transferring Energy
Energy can be transferred by:
o Emission or absorption of electromagnetic or nuclear radiation
o Heating and cooling an object or substance
o Applying a force on an object(mechanical energy transfer)
Kinetic Energy
 Kinetic energy is the energy associated with the movement of an object.
Unit 11.3: Energy Transformations in Collisions
When a vehicle collides with a stationary object or another vehicle the kinetic energy is
transferred and transformed into other forms of energy:
o Potential energy of deformation is the energy stored in an object as a result of
changing its shape i.e. the car panels.
Sound energy which is transferred to the surround air in a car crash and transmitted
by the vibration of the air particles.
Thermal energy is the energy that a substance possesses as a result of random
motion of the particles within the substance. In a collision, the vehicle's panels and
tyres get very hot as energy is transferred to the particles within them causing the
immediate surrounding objects to also be heated.
Unit 11.4: Momentum
Momentum is the product of the mass of an object and it's velocity. It is a vector quantity.
Impulse is the product of the force and the time interval over which it acts. It is a vector
quantity with units Ns.
Newton's Second Law of Motion states:
o The rate of change of momentum is directly proportional to the magnitude of the net
force and is in the direction of the net force.
Safety in Vehicles
 In a car collision the net force applied to your body can be controlled in two ways:
o Reducing your initial momentum and therefore your change in momentum by driving
slower. This is the purpose of low-speed zones, speed humps and speed limits.
o Increasing the time interval during which the change in momentum of the car and its
occupants occurs e.g. crumple zones.
 The front and rear areas of cars are designed to crumple and extend the time interval of a
 The passenger compartment is surrounded by a rigid frame to prevent the engine from
breaking through and thicker windscreens and side windows prevent the roof from collapsing
 Inside, padded dashboards, collapsible steering wheels and airbags protect passengers by
reducing the rate of change of momentum.
 Inertia-reel seatbelts allow occupants some freedom of movement but lock into place in the
event of a sudden change in velocity. When the car stops suddenly, the pendulum inside
continues forward preventing the belt reel from turning.
 In electronic sensor seatbelts, an electronic sensor releases a gas propellant when it detects an
unusually large deceleration causing the reel to be locked.
Unit 11.5: Momentum and Newton's Third Law of Motion
Conservation of Momentum
 The Law of Conservation of Momentum states that if there are no external forces acting on a
system, the total momentum remains constant.
 When two cars collide:
o The total momentum of the system remains constant
o The total change in momentum is zero
o The change in momentum of the first car is equal and opposite to the change in
momentum of the second car.
o The force that the first car exerts on the second car is equal and opposite to the force
that the second car exerts on the first car.
Chapter 12: The Big-Bang Cosmology
12.2: Historical Development of Models of the Universe
The Ancient Greeks
 Aristotle(384BC-322BC) believed:
o The Earth was at the centre of the universe and that the Sun and all the stars revolved
around the Earth. This is known as the geocentric model.
o There were 55 concentric spheres rotating around the Earth to which the stars and
planets followed
o All things on the Earth were made up of four elements: fire, air, water and earth and the
heavens were made of a fifth element called quintessence.
 In 240BC, Aristarchus proposed that:
o The Sun was much bigger than the Earth
o The Sun was at the centre of the Universe and that the Earth orbits it
o The Earth rotates on an axis once per day, producing the apparent motion of the Sun
and stars
 This is known as the heliocentric model which was very close to the truth but did not gain
favour because it was not sufficiently detailed to allow predictions that Aristotle's model did.
 In 140AD, Ptolemy refined Aristotle's model with circles within circles that successfully
predicted the movements of the stars and planets that was adopted by the Roman Church and
lasted for 1400 years.
Nicholas Copernicus (1473-1542)
 In 1514, Copernicus proposed that the Sun was stationary at the centre of the universe and
that everything else revolved in circles about it.
His discussions on the matter were done quietly until 1543 just before his death when he
published it formally.
 The church branded his work as heretical (against the church) and consequently it was a risky
theory for scholars to accept.
Tycho Brahe (1546-1601)
 Tycho Brahe was able to plot and observe the night sky with extreme accuracy using his own
astronomical measuring instruments. (0.5 arc minutes compared to other astronomers who
were limited to 15 arc minutes)
 Brahe's model of the universe was a combination of geocentric and heliocentric where all the
planets but Earth revolved around the Sun and the Sun revolved around a stationary Earth.
 The technology at the time failed to prove that the Earth was in motion as the evidence
required would come from a shift in the positions of some stars as the Earth moved called
 The largest parallax of any star is less than one second of an arc or a thirtieth of Brahe's best
measurements hence why he found it difficult to reject the geocentric model.
Johannes Kepler (1571-1630)
 Kepler who was Brahe's assistant inherited all of Brahe's data and applied it to Copernicus'
 In the early 1600s, he proposed an improved heliocentric model where the planets moved in
ellipses rather than circles consisting of three laws:
o The Law of Ellipses: each planet moves in an ellipse with the Sun at the focus.
o The Law of Areas: the speed of planets is such that they cover equal areas in equal
periods of time i.e. the closer the planets the faster they travel
o The Law of Periods: the period(T) of the orbit of a planet(time it takes to complete an
orbit) is related to the average radius of the orbit:
Note that if the period is in years and the radius is in AU (1 AU = the average radius
of the Earth’s orbit), then k = 1.
 Kepler's model was able to more accurately predict the motion of the planets than Ptolemy's
model so for the first time scholars had good scientific reasons to adopt the heliocentric
Galileo Galilei (1564-1642)
 Galileo believed in the Copernican model in secret as in 1600 an Italian philosopher had been
burned at the stake.
 Galileo heard about the invention of the telescope in 1608 and developed his own becoming
the first person to point one at the night sky.
 He made many discoveries using the telescope such as that Jupiter had four moons orbiting it.
The fact that the moons were orbiting Jupiter not the Earth proved that Ptolemy's geocentric
model was false and favoured Copernican's model.
 Galileo was placed under house arrest for the last nine years of his life but not before
publishing his findings and disproving the geocentric model.
Isaac Newton (1643-1727)
 Newton realised that the force of gravity held the Moon in it's orbit around the Earth and the
Earth around the Sun.
 Edmund Halley proposed that the force acted between the Sun and the planets was inversely
proportional to the square of the distance of the planet from the Sun:
Newton used this idea to deduce his Law of Universal Gravitation which states that the
gravitational force of attraction(F) between two masses is proportional to their product and
inversely proportional to the square of their separation distance:
This proved the physics of planetary orbits on mathematical evidence from which Kepler's laws
can be derived.
12.3: An Expanding Universe
Albert Einstein(1879-1955)
 In 1905, Einstein published the beginning of his Special Theory of Relativity that predicted
when you try to accelerate an object up to the speed of light, some of the energy is converted
into more mass making it bigger and harder to accelerate so that it can't have enough energy
to reach the speed of light: E = mc2
 In 1915, Einstein proposed the General Theory of Relativity that stated large masses have the
ability to warp space-time that affects the way masses move i.e. planets that appear to move
in a curved path are actually following straight paths through curved space-time.
 This theory was later proven by 3 experiments:
o The theory predicts that orbits of the planets would precess, that is, the long axis of the
elliptical orbits would itself slowly rotate about the Sun which was verified by all the
o The theory predicts that even light rays should be affected by warped space-time and
should curl around stars verified in 1919 and dubbed gravitational lensing.
o The theory predicts that time should run slower near an objects as large as a planet also
verified in 1962.
Aleksandr Friedmann (1888-1925)
 Friedmann proved that the universe must be expanding based on the theory of general
relativity (where Einstein thought the universe was static).
 He made two assumptions:
o That the universe appears identical whichever direction you look
o This is true whatever your viewpoint in the universe.
 From this, Friedmann discovered the closed universe, one of three possible scenarios:
o In the closed universe, the mutual gravitation of all the matter in the universe stops the
expansion and then pulls all the matter back together causing the universe to contract
o In the flat universe, the expansion of the universe is just fast enough to balance out the
force of gravity so that expansion slows but never stops.
o In the open universe, the universe expands so fast that expansion can't stop it.
Edwin Hubble (1889-1953)
 Hubble discovered the galaxy Andromeda, the first evidence that there was more than one
galaxy in the world.
 He made another discovery by studying the red shift of light from galaxies:
o The red-shift effect originated from spreading incoming light through a glass prism to
identify where in the light spectrum the wavelengths are.
o Vesto Sliper discovered that the light from nebulae(actually galaxies) were closer to the
red end of the spectrum i.e. red-shifted
Hubble discovered that almost all galaxies were red-shifted meaning they were moving away
from us and discovered a direct relationship between the distance of a galaxy and it's apparent
o The further away a galaxy is, the faster it is receding from us.
v = velocity of recession(kms-1), D = distance(mega parsecs[Mpc]), H0 = Hubble's constant
= 70kms-1Mpc-1
o One parsec = 3.26 light years, hence one mega parsec = 3.26 million light years
Hubble's constant was a measure of the rate of expansion of the universe based on the age of
the universe.
Hubble's discovery that the universe was expanding with the outer parts moving the fastest
implied that at some stage in the past the universe was concentrated at a single place called a
singularity and known as the big bang.
Cosmic Radiation Background
 Cosmic background radiation is a pattern of background radiation from space that represents
the afterglow of the heat of the early universe. Today it is found in the form of microwaves.
 Two engineers, Arno Penzias and Robert Wilson, discovered this when the radiometer built
into their telescope picked up a persistent microwave noise coming from the Earth, the solar
system and even beyond the galaxy.
 This turned out to be the cosmic radiation background predicted by Robert Dicke.
12.4: The Big Bang
In 1931, Georges Lemaitre suggested that the universe started out as a single 'space particle'.
In 1948, George Gamow suggested that the expanding universe started out as a hot, dense
concentration of matter that exploded out.
 In 1970, Stephen Hawking and Roger Penrose proved mathematically based on general
relativity that the universe began with a big bang.
The Expansion and Cooling
 The beginning of space and time was at 10-43seconds right after the moment of the big bang.
From then:
o The universe began a period of rapid exponential expansion driven by massive particles
called inflatons which have repulsive, anti-gravitational effects.
o Inflatons decayed into quarks and electrons and the quarks combined to form neutrons
and protons
o Thermonuclear fusion occurred within the universe which was in a hot and highly
ionised state of matter called plasma forming deuterium, helium and lithium.
o The radiation (including light) trapped within the plasma was released converting the
universe from being opaque to black and transparent.
12.5: Star and Galaxy Accretion
Cosmic background radiation showed that the distribution of matter was uneven and had
degrees of lumpiness.
This was necessary for the formation of stars and galaxies as an evenly distributed cloud of
matter would have equal pulls of gravity in every direction.
With a lumpy cloud of matter, areas of higher density would have greater gravitational
forces attracting more and more matter growing further in density. This is called
Chapter 13: Star Light, Star Bright
13.1: A Star's Luminosity and Brightness
Luminosity is the total energy radiated by an object per second measured in joules per second
or watts(like power).
 The Sun's luminosity is approximately 3.83 x1026W which is designated as L0.
 The brightness of a radiant object is the intensity of light as seen some distance away from it.
It is the energy received per square metre per second.
Inverse Square Law
Note that:
13.2: Temperature and Colour
A black body is one that absorbs all radiation falling upon it. When it becomes hotter than
its surroundings, it begins to radiate electromagnetic energy of its own called black-body
The radiation I is distributed continuously but not evenly across the various wavelengths
of the electromagnetic spectrum. It depends on the temperature:
o Increasing temperatures correspond to shorter wavelengths whereas decreasing
temperatures correspond to longer wavelengths.
o This relationship is known as Wien's Law:
There is a correlation between a star's surface temperature and it's colour:
o A cooler star with a surface temperature of about 3000 or 4000K produces most of
its visible radiation at the red end of the spectrum.
o At higher temperatures, the wavelengths exist around the yellow part of the
o At even higher temperatures, the radiation is more evenly distributed producing a
white appearance.
o Even hotter stars produce most of their visible radiation at shorter wavelengths
appearing blue.
13.3: The Hertzsprung-Russel Diagram
Ejnar Hertzsprung devised a diagram that graphs a star's luminosity against its temperature or
colour mainly used to compare groups of stars.
The axes are not linear with the vertical scale increasing by a factor of 10 and the horizontal
scale doubles from right to left.
Identifiable Star Groups
 The main sequence is a diagonal band from the upper left corner to the lower right corner of a
H-R diagram containing most of the stars.
 The red giants is the group of stars in the upper right corner of a H-R diagram that represent
cooler but more luminous and much bigger stars.
 The white dwarfs is the group of stars in the lower left corner of a H-R diagram that represent
smaller low luminosity stars that are really hot.
13.4: Energy Sources within Star Groups
There are two forces acting on a star that determine its size:
o The inwards force of gravity trying to compress the star
o The outwards force of the star's radiation pressure resulting from the nuclear reactions
within the star.
 Different radiation pressures result from different nuclear reactions in different stars. Without
this pressure, the star would get crushed by its own gravity.
Nuclear Fusion
 The fusion of hydrogen to form helium inside a star is achieved through either the carbonnitrogen-oxygen cycle or the proton-proton chain where four hydrogen nuclei join to form a
single helium nucleus releasing two positrons (anti-electrons), two neutrinos and some
Three helium nuclei can fuse to form a single carbon nucleus releasing gamma radiation as
well as some energy in a reaction called the 'triple-alpha reaction'.
In more massive stars, carbon can fuse with helium to form oxygen.
Stages of a Star
 Protostar stage:
o A star begins its life as a contracting gas cloud predominantly hydrogen with some
o As the cloud contracts it heats up forming a protostar and if big enough the fusion of
hydrogen will begin. If it is too big, the radiation pressure will instantly blow it apart.
o Once fusion of hydrogen begins the proto star becomes a main-sequence star producing
helium and remaining in this state until it runs out of fuel.
 Red-giant stage:
o When the radiation pressure begins petering out, the star's core shrinks and the
remaining hydrogen fusion shifts to a shell that expands and cools as it becomes less
o When the core collapses, the pressure and temperature suddenly increases starting the
fusion of helium to carbon if the star is big enough.
 White-dwarf stage:
o When the helium-fusing core of a red giant runs out of fuel, the star will contract again
shedding its outer layers into planetary nebula and contracting into a hot dense white
dwarf which will eventually cool into a black dwarf.
o Bigger stars will lose its outer layers in an enormous explosion called a supernova and
the remaining star corpse will be much denser than a white dwarf either as a neutron
star or a black hole.
Chapter 14: The Sun-Earth Connection
Unit 14.1: Nuclear Radiation
There are three types of nuclear radiation: alpha, beta and gamma each with a different
charge, ionising and penetrating ability.
The three types of radiation also follow different paths
when they travel through a magnetic or electric field:
 Beta and alpha radiation move in different directions due
to their opposite charges and beta radiation moves off in a
tighter turn due to it being lighter.
Binding Energy
 The mass of an atomic nucleus is less than the sum of the
masses of the individual parts. The missing mass called the
mass defect has an energy equivalent found by E = mc2
called the binding energy.
 This is the amount of energy needed to split the atomic
nucleus into its separate protons and neutrons.
 The greater this energy, the more stable the nucleus of the atom is.
Unit 14.2: The Sun
The Sun is a ball of gas consisting of mostly hydrogen and helium superheated into a plasma.
The Sun is a second generation star evident from its composition: 73.4% hydrogen, 25%
helium and 1.6% of its mass being heavier elements that were not produced by the big bang
but in a red-giant star during its lifetime or its supernova.
 Every second 600 million tonnes of hydrogen are fused into 595 million tonnes of helium
releasing 5 million tonnes of energy.
 The Sun is one star of 100 billion in our galaxy which is one galaxy of 100 billion though to exist
in the universe.
 The inner structure of the sun consists of four layers:
o The core: innermost layer where energy production by fusion of hydrogen and helium
o The radiative zone: electromagnetic energy is transmitted slowly through this layer by
absorption and re-radiation
o The interface zone: thin layer that generates the Sun's magnetic field.
The convection zone: energy is transmitted through to the surface by convection
 The surface is called the photosphere, a gaseous layer several hundred kilometres thick
emitting mostly EM radiation in the visible spectrum hence it is visible.
 The Sun's atmosphere(only visible during a solar eclipse) consists of three layers:
o The chromosphere immediately above the photosphere
o The transition region: a few hundred kilometres thick
o The corona: the outer atmosphere that extends many millions of kilometres into space
without an abrupt end forming solar wind and whatnot.
 The Sun produces two types of emissions:
o Electromagnetic radiation
 The sun produces EM waves from the short-wavelength gamma rays to the long
radio waves but mostly in the visible spectrum.
 It takes about 8 mins at the speed of light to get to the Earth.
o Solar wind.
 The difference in pressure between the corona and the interplanetary space
causes an outflow of low-density plasma called solar wind.
 The magnetic field generated by the moving charges of the plasma become
interlocked with the magnetic field lines of the Sun. The solar wind carries the
magnetic field out into space while the magnetic field lines remain anchored to
the surface of the sun creating the interplanetary magnetic field.
 Granulation
o The photosphere is covered in granules about 500-1000k's across with a lifetime of
about 8 mins as the currents shift. Each granule is the top of a convection current.
 Spicules
o These are short-lived jets of gas that rise several thousand kilometres above the surface
seen around the edges of sunspots and granules.
 Sunspots
o These are dark spots that appear dark because they are about 1500K cooler than their
surroundings. These regions have intense magnetic activity of about 0.4tesla where
magnetic field lines have looped out and back into the surface of the Sun. The intense
field activity prevents the convection of heat to the surface.
 Flares
o Solar flares are explosive outbursts of radiation and matter near sunspots that last about
an hour. They emit radiation bursts within the radio to X-ray range while the outburst of
matter is called a coronal mass ejection.
o Solar flares occur when magnetic field lines become so twisted that they snap and rejoin releasing a large amount of energy.
o These are large looping curtains of gas that are supported by magnetic field lines
creating an arched shape. They can cause material to be thrown out into the corona.
 Coronal Holes
o Coronal holes appear in sections of the corona especially over the solar poles and are
the primary source of fast solar wind.
 Coronal Mass Ejections(CME)
o CMEs are large magnetically confined bubbles of plasma containing up to ten million
million kilograms of coronal material that expand and accelerate away from the Sun and
are produced by solar flares or prominences.
The Solar Cycle
 The solar cycle is an 11-year cyclical pattern of increasing and decreasing frequency of
sunspots, flares, prominences and CMEs.
o The period of peak activity is called solar maximum (often with over 100 sunspots
appearing) and the opposite is called the solar minimum.
 The sunspot cycle is a cyclical pattern of increasing and decreasing numbers of sunspot.
o Sunspot frequency can be monitored by counting the number of sunspots daily or
tracking the latitudes at which the sunspots are appearing.
o Higher latitudes occur early in the cycle, whereas later in the cycle sunspots appear near
the solar equator.
Unit 14.3: The Sun-Earth Connection
The Electromagnetic Connection
The Solar Wind Connection
 The interplanetary magnetic field carried by the solar wind interacts with the Earth's magnetic
 Most of the solar wind flows around and past the Earth distorting the Earth's magnetic field
into a long tail shape.
 The region surrounding a planet containing its distorted magnetic field is called the
 The ions of the solar wind can enter the magnetosphere by three ways:
Through cusps and holes in the magnetosphere over the North and South poles
Through the magnetotail and back up towards the Earth
Through some leakage in the magnetopause
Once inside, the ions are captured by Earth's magnetic field lines and spiral from one pole to
the other and bounced back accumulating in two zones called Van Allen belts.
The movement of these charged particles form a ringed current which produces a magnetic
field that can interfere with the Earth's field which contributes to the effects of a geomagnetic
storm (a period when the Earth's magnetic field experiences unusual distortions and
fluctuations in strength).
Space weather refers to major disruptions in the speed, density and temperature of solar
winds that the magnetosphere is vulnerable to.
Turbulent space weather can result in:
o Abnormal heating of the atmosphere causing it to expand slightly and increasing drag on
satellites causing them to decay out of their orbits
o Higher risk of radiation exposure for astronauts, satellites and spacecraft
o Electrical failure of communication satellites
o Strong geomagnetic storms that can produce auroral displays but send huge current
spikes through power grids
o Fluctuations in Van Allen belts and the ionosphere disrupting communications
Study collections