Appliances are used to transfer heat. However, how well they manage depends on their efficiency and how cost effective they are.
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Energy transfer
First of all, it’s important to understand that there are different forms of energy.
| Energy type | Description |
| MagneticKinetic (movement)Heat (thermal)Light
Gravitational potential Chemical Sound Electrical Elastic potential Nuclear |
This is the energy found in magnets and electromagnetsThis is the energy found in moving objectsThis is also known as thermal energyThis is also known as radiant energy
This is the energy stored within raised objects This is the energy stored on foods and fuels This is released when objects vibrate This is the energy found in moving charges Energy stored in objects while squashed or stretched This is the energy stored in the nuclei of atom |
One way to remember them all is will the following sentence:
Most Kids Hate Learning GCSE Energy Names
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Energy transfer diagrams
It’s possible for one energy type to be transferred to another using an appliance. The energy being transferred can be represented in an energy transfer diagram.
For example, a light bulb takes in electrical energy and converts it into light energy.
However, when you touch a light bulb that’s been on for a while it’s hot. This is because a bulb also gives out energy as heat. This heat is a non-useful form of energy. An energy transfer diagram doesn’t show this because it only provides useful energy transfers.
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Sankey diagrams
Sankey diagrams, on the other hand, provide all the energy transfers that take place.
In your exam you might be asked to sketch a Sankey diagram. However, if a Sankey diagram is drawn to scale then you can use it to work out the exact efficiency of an appliance.
As you can see, even though a light bulb is used for light energy, most energy is in fact lost as heat. This lost energy is known as ‘wasted’ energy: it’s simply lost to the surroundings, heating them up until it’s too spread out to be of any use.
As well as being transferred, energy can also be stored or dissipated. However, it can never be either created or destroyed.