Physics March Test : Energy


Energy changes, eficiency, renewable and non renewable fuels etc.

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Energy (general)

Energy is the ability to do work.

' Energy cannot be created or destroyed, only transferred from one form to another'

All types of energy are measured in JOULES (J)
THE SUN is the ultimate source of nearly all our energy.

There are 9 main types of energy :

  • Heat - fire, radiator
    Kinetic (movement) - fan, tennis ball
    Nuclear - nuclear bomb, sun
    Sound - Buzzer, speakers
    Light - fire, sun, light bulb
    Chemical - humans, animals, food
    Gravitational Potential - bouncing ball, bungee jumper
    Elastic potential - bungee, slinky
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Energy: Changes, efficiency


To describe an energy change we need to use an arrow. eg.

Electrical energy -> light + heat

electric fire
Electrical energy -> light, heat and sound


Efficiency is a measure of how much useful energy you get out of an object from the energy you put into it. Efficiency DOESN'T have any units.

Efficiency = Useful energy transferred by device/
total energy supplies to device.

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Energy : Fuels

A fuel is something that releases energy.

Coal, oil, natural gas and wood are examples. Coal, oil and natural gas are all also fossil fuels and will eventually run out. Wood is a renewable energy source.

Fossil fuels are made from remains of plant (coal) and animal (oil and gas) matter.

The original source of energy from fossil fuels is the SUN due to PHOTOSYNTHESIS.

Non renewable = being used up faster than they can be replaced.

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Power stations

Traditional (fossil fuels):

In a coal/oil fired power station, burning fuel heats water to produce steam. The steam drives a turbine, producing electricity.

In a gas fired power station, we burn natural gas in a gas turbine engine. This makes a powerful jet of hot gases and air which drives turbines.

Energy Flow diagram:


The fuel used is uranium. Nucleus oF uranium atom is unstable and can split into 2, enery is released when that happens. This is called nuclear fission.

Thermal energy is used to turn water into steam which drives turbines and is electricity.
Energy Flow diagram:

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Heat transfers

Conduction: ( mainly occurs in solids)

Some non- metals are good conductors of heat (eg. graphite). As the solid is heated, the carbon atoms near the heat source will begin to vibrate, which make the next atoms along vibrate etc.

Metals which are good at conducting heat (eg. copper) have free electrons which can move around in between atoms. The electrons help transfer heat energy faster. When rod is heated copper atoms pass on energy. Electron also gives energy, but are free to move aroung, this allows them to spread atoms further away.

Convection: ( Only occurs in liquids or gases)

Kettle: When kettle turned on, heating element warms up and heats water around it, which expands and rises up the kettle. It then displaces the cold water, which falls to the bottom and is then warmed by heating element. This creates circular movements known as CONVECTION CURRENTS. This process continues until water reaches boiling point.

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Heat transfers contnd.

Radiation: (through any material, even vacuum)

Infra-red (IR) radiation is an electro magnetic wave.
Dark, matt colours absorb AND emit IR radiation. Light, shiny colours reflect it.


Evaporation occurs when particles in a liquid escape to form a vapor.
It can take place at any temperature, but occurs most rapidly at liquids boiling point.
Particles which escape take some energy from the remaining particles, so the trmperature of the liquid falls.

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Vacuum Flask


Rubber/ plastic lid: prevents leacking, convection and evapouration

Double walled glass/plastic container: made of poor conductors

Silvered Surfaces: prevents radiation

Vacuum: prevents conduction and radiation

Plastic protective cover

Sponge pad: for protection

Plastic spring: for support

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Home insulation

Heat loss stats.:

Walls = 36%
Floors = 28%
Roof= 20%
Windows = 12%
Doors= 4%

Cavity wall insulation: Without insulation, there are convection currents in cavity. With foam insulation this is prevented.

Loft Insulation: Aims to prevent convection and a bit of conduction

Double Glazing: Prevents conduction.

Other methods are: fibre glass (loft), draught excluders, carpets and curtains.

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Payback time

" Payback time is the time that a form of insulation in a house takes to save the owner the money that it cost to install"

Payback time (Years) = Cost of installation (£)
Annual Saving (£)

Draught proofing and hot water jackets have the quickest pay back time, whilst double glazing has the most.

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