Energy and energy Energy and energy resources summaryresources summary

10 April 2023

Thermal radiationThermal radiationHot objects emit thermal radiation (infra red rays) which are part of the electromagnetic spectrum.

The hotter an object is the more thermal radiation it emits.

Dark coloured, matt surfaces are better emitters and absorbers of thermal radiation (heat).

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ConductionConductionHeat can be conducted by a

substance as one particle collides with the particle next to it.

Metals are very good conductors of heat because free electrons easily transfer the energy as they diffuse through the metal .

Non metals and particularly substances that contain air are very poor conductor (also called insulators)

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ConvectionConvectionConvection occurs in fluids

(liquids or gases) as the hot (lower density) fluid rises and the cooler (higher density) fluid sinks.

Convection cannot take place in solids because the particles are not free to move.

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Heat transferHeat transferHeat can only pass through a

vacuum by radiation since there are no particles in a vacuum to allow for conduction or convection.

Houses can be insulated against heat loss by wall insulation, double glazing, loft insulation and draft excluders.

Small objects (bigger surface area in relation to their size) lose heat faster than large objects

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Forms of energyForms of energyEnergy can exist in a variety of forms:Chemical energy – stored in food or fuel.Kinetic energy – in moving objectsGravitational potential energy – due to

position of an object above ground.Elastic energy – stored in springy

objectsElectrical energy – carried by moving

charges in a current.Thermal energy – energy in particles of

a hot object

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Transformation of energyTransformation of energyEnergy can be transformed from one

form to another.When this happens no new energy is

created or destroyed it simply changes form – this is called conservation of energy.

In many cases the energy is transformed into heat energy in the surroundings. As this happens the energy becomes more diluted and is very difficult to reuse.

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Useful energyUseful energyUseful energy is energy which is

transformed for the purpose for which it was intended. Example electrical energy can be usefully converted into light.

Wasted energy – this is energy which is transformed into a form which was not intended and often results in the surroundings becoming warmer. Example – the electric light also heats the room. Wasted energy generally results in an effective loss of money.

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EfficiencyEfficiencyEnergy is measured in Joules (or

kilojoules)Energy supplied = useful energy

+ wasted energy.Efficiency = useful energy / total

energyEfficiency is often expressed as a

percentage.

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Electrical devicesElectrical devicesElectrical devices transform the

kinetic energy of the moving charges in the current into various other energy types.

Examples are: light (lamps), heat (ovens), sound (radios), movement (motors).

Most electrical devices also waste energy – usually as thermal energy.

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Electrical powerElectrical powerThe unit of power is the watt (W),

1 watt = 1 Joule/second.1 kilowatt (kW) = 1000 watts (W)Power is the rate at which energy

is transformed.Formula:Power (W) = energy (J) / time (s)

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Using electrical energyUsing electrical energyElectrical energy used is measured in

kilowatt hours (kWh).1kWh = 1000 watt appliance used for 1 hour.Cost = number of units x cost per unit.1 unit costs about 15p at present –

this is going up rapidly!Example: Cost of using a 2000 watt

heater for 3 hours will be:Cost = 2kW x 3 hours x 15p = 90 pence

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The National GridThe National GridThe National Grid is the cables and

transformers that supply homes and factories with electrical power.

Step up transformers are used to produce very high voltages in overhead cables (about 130000V) – this reduces heat loss in the cables because the current is very small.

Step down transformers are used to provide safe voltages (230V) for homes.

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Fuel for electricityFuel for electricityThe diagram shows the basic parts of a

power station. The heat is produced by often burning fossil fuels.

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Energy from wind and Energy from wind and waterwaterWind and water can spin an

electrical generator in these ways:Wind turns the turbine blades.Waves produce a rocking motion.Water flows through tidal barrages

and hydroelectric dams.All these produce renewable,

pollution free electricity but all can damage the environment and are unsightly.

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Energy from the Sun and the Energy from the Sun and the EarthEarthSolar cells can produce electricity

when light falls on them – this is an expensive way to make electricity.

Solar panels can heat water.Geothermal power stations use

steam produced by radioactive substances underground drive a generator. This is a renewable energy source but is not available in many places.

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Energy and the Energy and the environmentenvironmentBurning fossil fuels like coal

produce carbon dioxide (a greenhouse gas) and acid rain.

Nuclear fuels do not produce greenhouse gases and use a very small volume of fuel but the radioactive waste is very difficult to store and remains dangerous for many years.

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