P2b(ii) Generating Electricity

You will learn about:How electricity is carriedHow electricity is made

Energy Efficiency

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Carrying ElectricityThere is a network of power cables around the country that transmits electricity. This is known as the National Grid.The National Grid carries electricity to consumers such as homes, farms, schools and hospitals.

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Electricity is generated in a power station with a voltage of 25,000 Volts. A step-up transformer increases the voltage along the pylon’s transmission lines to 400,000 Volts. From there step-down transformers reduce the voltage until it is safe enough to be used. The mains electricity in our homes uses 230 Volts. So the voltage needs to be stepped down several times before the electricity is carried to our homes.

Transformers

Step Up : Up the Voltage

Step Down: Down the Voltage

Power Station GeneratorsJust like a dynamo, a generator in a power station uses the same ideas: a magnetic field rotates relative to the coil which produces a voltage.

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In a power station the magnet and coils are much, much larger!

In the power station generator the coil of wire is able to rotate freely between the poles of two magnets. When the coil turns it cuts the magnetic field so a current passes through the coil.Just like the dynamo the same would happen if the coil did not move and the magnets did.

The generator does not turn by itself.Huge amounts of coal are pulverised and burnt to produce heat.This heat boils water turning it into steam.The steam turns a turbine.The turbine turns the generator.The generator generates electricity.

Coal

Water

Steam

Turbine

Generator

EfficiencyWe have met efficiency before in P1 and the equation to use is the same:

efficiency = x 100

For every 100J of energy in a power station 15 J is wasted in the boiler and 45 J are wasted in the cooling towers and a further 5J wasted in the generator.

This means that in total 65J are wasted and 35J are transferred into useful electricity.

We can work out the efficiency:efficiency = x 100

Efficiency = x 100 = 35%

www.PhysicsGCSE.co.uk REMEMBER:Due to the size of the power station a lot of energy is wasted. Energy is wasted as heat and sound in the boiler and at the turbine and also in the generator.

Questions

1. A cooling tower in a power station cools what?2. Define the term ‘consumer’.3. Describe what happens to water in a power station.4. A power station has 80% of its energy lost to the

environment. How efficient is it?5. Why do the magnet or coil need to rotate relative to one

another?6. A power station is 40% efficient. It produces 3 million

Joules of electrical energy each second. How many Joules of energy are lost to the environment each second?

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Questions

1. A cooling tower in a power station cools what? Water2. Define the term ‘consumer’. A person who purchases and uses electricity such as a

house or shop owner.3. Describe what happens to water in a power station. It gets heated

and turned into steam. After turning a turbine it is cooled in the cooling towers and condensed back into water to be used again. Some water leaves the power station as water vapour which is seen as the gas leaving a chimney. That dense white smoke is just water even though it looks rather nasty!

4. A power station has 80% of its energy lost to the environment. How efficient is it? 100 – 80 = 20% efficient.

5. Why do the magnet or coil need to rotate relative to one another? The magnetic field needs to be cut to allow current to be produced in the coil of wire. If neither moved then current will not be produced.

6. A power station is 40% efficient. It produces 3 million Joules of electrical energy each second. How many Joules of energy are lost to the environment each second? The power station is 40% efficient which means that 60% of energy is wasted to the environment. So we need to calculate 60% of the total 3 million Joules of energy. So we work out 1% : and multiply by 60 = 1,800,000J.

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