# Physics P1 Notes X

Physics P1 Notes for AQA GCSE

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Physics Notes
P1a
Heat Transfer
Thermal radiation is energy transfer by electromagnetic waves.
The hotter an object the more thermal radiation it emits (gives out).
Radio waves, microwaves, infra-red radiation, visible lights and X-rays are all part of the
electromagnetic spectrum.
Dark matt surfaces are better emitters and absorbers of thermal radiation than light shiny
surfaces.
Metals conduct heat better than non-metals.
Conduction is when metals contain free electrons, which move about at random and collide
with each other. When one end of the metal gets hot, the free electrons get kinetic energy
and move faster, colliding with other free electrons, so the kinetic energy is transferred.
Non-metals are poor conductors because they have no free electrons.
Convection is the heat transfer in a liquid or gas due to circulation (convection) currents.
Convection currents are caused when the fluids rise when they are heated and fall when they
cool down.
Large surface area loses heat not that easily.
Small objects lose heat more easily then large objects.
The vacuum between the walls cuts out heat transfer by conduction and convection.
Glass is a poor conductor, so less heat conduction.
The glass surfaces are silvery to reduce radiation from the outer wall.
Using Energy
Chemical energy is stored in a fuel. It is released when chemical reactions take place.
Kinetic energy is the energy of a moving object.
Gravitational potential energy is when something goes up e.g. rollercoaster.
Elastic (strain) energy is the energy stored in a springy object when we stretch or squash it.
Electrical energy is energy transferred by an electric current.
Thermal (heat) energy is because of the temperature.
Energy can change from one form to another.
The conservation of energy tells us that energy cannot be created or destroyed, just
changed from one form to another.
Useful energy is the energy that we need.
Wasted energy is energy that is not useful.
Useful energy and wasted energy both end up being transferred to the surroundings, which
become warmer.
As energy spreads out, it gets more and more difficult to use for further energy transfer.
Weight is measured in Newton's. 1 kg on earth = 10N.

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Energy is measured in joules.
Energy supplied = useful energy + wasted energy.
Efficiency = useful energy / total energy supplied.
Electrical energy
Electrical energy is energy transfer due to an electric current.
The energy supplied per second to the motor, is the power supplied to it.
Power is measured in watts (W) or kilowatts (kW)
1 watt = 1 J/s
1 kilowatt = 1000 watts.
Power (W) = energy transferred (J) / time taken (s)
Power is the rate of transfer of energy.…read more

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Tidal power ­ The water after each tide is kept behind a barrage. The high tide is released in
sea, which turns the turbine, which turns the generator producing electricity.
Solar cells convert the energy they absorb into electrical energy. They are useful in small
amounts. They are expensive but cost nothing to run. You need sun.
Solar heating panels heat water the flows through it.
Geothermal energy comes from the energy released by radioactive substances deep inside

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wavelength.
Ultraviolet radiation makes some chemicals emit light.
Ultraviolet radiation is harmful to human eyes and causes blindness. Ultraviolet (UV)
wavelengths are smaller than light wavelengths so they carry more energy and cause
sunburn and skin cancer.
Infra-red radiation damages or kills skin cells because it heats up the cells.
Microwaves are used for:-
Communication because they pass through the atmosphere and reach satellites orbiting
the Earth.

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A plant or wood (carbon) has a half life of 5600 years.
The Origins of the Universe
The wavelength of light increases across the spectrum from blue to red.
The light waves are spread out if the star or galaxy is moving away from us. We call this a red
shift.
The light waves are squashed if the star or galaxy is moving towards us. We call this a blue