Physics GCSE AQA Core Revision

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Physics ­ Core Revision notes
Heat transfer
Atmosphere protection
Radio waves, microwaves, infra-red radiation and visible light are part of the
electromagnetic spectrum. Electromagnetic waves are electric and magnetic waves that
travel through space.
The sun emits radiation in all parts of the electromagnetic spectrum and we are protected by
the atmosphere which blocks most of the radiation such as ultraviolet.
The Earth's atmosphere acts like a greenhouse made of glass. In a greenhouse, shorter
wavelength radiation from the sun can pass through the glass. However, longer wavelength
thermal radiation is trapped inside by the glass so the greenhouse stays warm.
Gases in the atmosphere such as water vapour, methane and carbon dioxide, act like the
glass. They trap the thermal radiation given off from the Earth which makes the Earth much
Surfaces and radiation
Dark, matt surfaces emit more radiation than light, shiny surfaces
Dark matt surfaces absorb radiation better than light, shiny surfaces.
A matt surface absorbs radiation better than a shiny surface because it has lots of cavities
which trap and absorb the radiation.
Incident Incident
radiation radiation
Matt surface Smooth surface
Metals conduct heat better than non-metals
Metals contain lots of free electrons. These electrons move about at random inside the
metal and hold the positive ions together. They collide with each other and with the
positive ions.
+ Ions +
Atom +
Metal Non-metal

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When a metal rod is heated at one end, the free electrons at the hot end gain kinetic
energy and move faster.
o These electrons diffuse and collide with other free electrons and ions in the cooler
part of the metal
o As a result they transfer the kinetic energy to these electrons and ions.
In a non-metallic solid, all the electrons are held in the atoms. Energy transfer only takes
place because the atoms vibrate and shake each other.…read more

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Elastic (or strain) energy
Energy stored in springy objects when we stretch or squash them
o Electrical energy
Energy transferred by an electric current
o Thermal (heat) energy
Energy due to temperature. This is partly because of the random kinetic
energy of the particles of the object.…read more

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Worked example
An electric motor is used to raise an object. The object gains 60J of gravitational potential energy
when the motor is supplied 200J of electrical energy. Calculate the efficiency of the motor.
Total energy supplied to the device = 200J
Useful energy transferred to the device = 60J
Efficiency of the motor = useful energy transferred by the motor/total energy supplied to the motor
60J/200J = 0.…read more

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Using electrical energy
Energy transferred (kilowatt-hours, kWh) = power of device (kilowatts, kW) * time in use
One kilowatt-hour is the amount of electrical energy supplied to a 1 kilowatt device in one
hour. So 1 kilowatt-hour = 1000 joules/second x 60 x 60s = 3,600,000J
The electricity meter in your home measures the amount of electrical energy your family
uses. It records the total energy supplied, no matter how many devices you all use.…read more

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Generating electricity
Fuel for electricity
In a coal or oiled fired power station the burning fuel heats water in the boiler to produce
steam. The steam drives a turbine that turns an electricity generator
In a gas-fired power station, we burn natural gas directly in a gas turbine engine. This
produces a powerful jet of hot gases and air that drives the turbine.…read more

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A wave generator uses the waves to make a floating section move up and down. This motion
drives a turbine which turns a generator. A cable between the generator and the shore
delivers electricity to the grid system.
Wave generators need to withstand storms and they don't produce a constant supply of
electricity. Also, lots of cables (and buildings) would be needed along the coast to connect
the wave generators to the electricity grid. This would spoil areas of coastline.…read more

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Energy and the environment
Fossil fuel problems
o When coal, oil or gas a burnt the chemical reactions make `greenhouse gases' such
as carbon dioxide. These gases cause global warming.
o Burning fossil fuels can produce sulphur dioxide. This gas causes acid rain in the
atmosphere. We can remove the sulphur from a fuel before burning it to stop acid
rain. For example, natural gas has its sulphur impurities removed before we use it.
o Fossil fuels are not renewable.…read more

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Electromagnetic waves are electric and magnetic disturbances that transfer energy from one
place to another
o Electromagnetic waves do not transfer matter. The energy that they transfer
depends on the wavelength of the waves. This is why waves of different wavelengths
have different effects.…read more

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To kill cancer cells a narrow bean of gamma radiation is directed at the tumour. The
beam is aimed at it from different directions in order to kill the tumour but not the
surrounding tissue. Uses cobalt-60 which is stored in a thick lead container. When
not in use, it is rotated away from the exit channel.
Too much X-Ray or Gamma radiation is dangerous and may cause cancer High doses kill
living cells and low doses cause cell mutation and cancerous growth.…read more


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