# Energy

## Energy transfer - Types of energy

1. Electicial

2. Light

3. Sound

4. Kinetic (Movement)

5. Nuclear

6. Thermal (Heat)

7. Gravitational Potential

8. Elastic Potential

9. Chemical

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## Energy transfer - Conservation of energy

1. All energy comes from the Sun

2. Energy cannot be created or destroyed

3. We can only transfer energy from one type into another

4. Energy is only useful when it can be transferred from one form to another

Examples of energy transfers:

Bunsen burner - Chemical (gas) to Heat and Light

Generator - Kinetic (wind) to Electric and Heat

Catapult - Elastic Potential to Kinetic and Heat

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## Efficiency formula

Energy  =  Useful Energy out

Total Energy in

Example: A TV has an input energy of 220J. It gives out 5J of light energy, 2J of sound energy and 213J as heat energy. Work out the efficiency of the TV.

The light and sound energy are useful, but the heat energy is wasted, therefore:

Efficiency  =   5 + 2   =     7       =    0.0318   =  3.18%

220         220

• All appliances waste some energy
• This heat is transferred to cooler surroundings, which then become warmer
• As the heat is transferred to cooler surroundings, the energy dissipates - so it becomes less useful
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## Forms and uses of energy, energy transfer

Chemical energy - is energy stored in fuel(including food). This energy is released when chemical reactions take place.

Kinetic energy - is the energy of a moving object.

Gravitational potential energy - is the energy of an object due to it's position.

Elastic(or strain) energy - is the energy stored in a springy object when we stretch or squish it.

Electrical energy - is energy transferred by an electric current.

Thermal (heat) energy - of an object is energy due to its temperature. This is partly because of the random kinetic energy of the paricles of the object.

Cars, buses, planes and ships all use energy from fuel. They carry their own fuel. Electric trains use energy from fuel in power stations. Electricity transfers energy from power stations to the train.

efficiency = useful energy transferred by the device/total energy supplied to the device.

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