# Physics 1a

Need some help on Physics? Well thr these out for size and see if they help you pass your GCSE physics 1a exam.

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• Created by: Shanzii
• Created on: 02-02-09 15:29

## Heat Transfer

Heat is transfered in three different ways and they are:

• Conduction
• Convection

But what are these funny looking words well...

Radiation is the transfer of heat energy by Electromagnetic waves. Radiation occurs in solids, liquids and gases.

Conduction involve the transfer of energy by particles. It is also the main form of heat transfer in solids.

Convection also involves the transfer of energy by particles. It is also the main form of heat transfer in liquids and gases.

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## Heat Convection

CONVECTION occurs when the more energetic particles MOVE from the HOTTER REGION to the COOLER REGION - AND TAKE THEIR HEAT ENERGY WITH THEM!

CONVECTION CURRENTS are all about CHANGES IN DENCITY!

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## Calculate the efficency

Its really sinple to Calculate the Efficiency of a machine

You do it like this....

Efficency = Useful energy output devided by the total energy input

Just like that!

But - Nodevice is 100% efficent and the wasted energy is always diddipated as heat

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## The National Grid

The National Grid is a network of pylons and cables that covers the whole of Britain, gettign electricity to homes all over the country.

Electricity gets around via the National Grid by...

1) The National Grid takes electrical energy from the power stations to just where is needed in homes and industry

2) It then enables power to be generated anywhere on the grid, and then it can be suplied anywhere else on the grid

3) To transmit the huge amount of power needed, you need either a high voltage or a high current

4) The problem with a high current is that you lose loads of energy through hjeat in the cables

5) Its much cheaper to boost the voltage up really high (to 400 000 V) and keep the current very low

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