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Study Guide : Energy

Learner Guide


Energy in Food

We get our energy from the food we eat. The energy is released 

by combustion or respiration in our cells. The amount of energy

is usually shown as calories, however, the scientific term for 

energy is joules. There is a very large amount of energy in food,

so food labels often show the energy in kilojoules (kJ).


1000J = 1kJ


Different types of food have different amounts of energy, for 

example, an éclair has about 3140 kJ per 100g, whilst a peach

has 135 kJ per 100g.

Brisk walking uses up about 14 kJ per minute, so 100g of

peaches would give you enough energy for about 9.5 mins of 

brisk walking.



Electrical power is the rate at which energy is transferred. 

Power is measured in Watts (W). 1 Watt is 1 Joule per second,

which means a 20 W bulb uses 20 Joules per second.


Electrical appliances usually display their power on the label. 

Some appliances that use a lot of energy display their power

in kilowatts (kW).


1000 W =1kW

Electric companies use kWh instead of joules, which is the 

amount of energy used by a 1kW appliance in one hour.



Where does energy come from?

We get energy from non-renewable and renewable energy

sources. Most of the energy comes from fossil fuels, which 

are a non-renewable energy source.


Fossil Fuels

Fossil fuels were formed millions of years ago from dead 

organisms. Coal was formed from dead plant forms, crude oil

and gas were formed from dead marine organisms.

Fossil fuels are a finite energy source as they are being used 

up quicker than they can be remade. There is only a limited 

amount of fossil fuels in the world.


Most of the electricity in the UK comes from fossil fuels. The 

fuels are com busted, creating heat energy which is used to 

boil water. The steam turns turbines which then turn electrical

generators. The burning of fossil fuels releases gases into the

air which amount to pollution. The main gases produced from 

burning fossil fuels are carbon dioxide (which is a greenhouse

as that increases global warming) and sulphur dioxide and

nitrogen oxides (which cause acid rain, killing plants and


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Related Topics

Solids-liquids-gases                Forces-movement                           Electricity

Waves                                        Electromagnetism                            Space


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