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Physics - The National Grid (AQA Syllabus A)
When the National Grid was established, the cables were all carried by pylons.

Physics - The National Grid (AQA Syllabus A)

In GCSE Science students will look at electrical energy. This is the last of six quizzes on that subject and it looks at how electricity is transported via the National Grid.

The National Grid is the name given to the network of cables and transformers that transport electricity from the power stations in Britain to homes, factories, offices, shops and the other places that require it. It was created during the 1920s and 1930s in order to give the country a more reliable supply of electricity. Before the National Grid, power stations were owned by private electricity generating companies who had their own local electricity grids. These ran on different voltages so a kettle bought in Birmingham might not work in Lichfield, just 20 miles away!

Generators at the power stations produce electricity at 25,000 volts. Electricity transported, or transmitted, at that voltage over the distances covered by the National Grid would create high currents. The electricity would lose a lot of its energy as heat which would be very wasteful. To get round this, the electricity generated by the power station is passed through a 'step up' transformer, increasing the voltage to as much as 400,000 volts. This means that the current will be a lot lower. To understand how this works, think about the relationship P = V x I where P is power, V is volts and I is current. If you increase the voltage, the current must decrease. With a lower current, there is less of a heating effect and so less energy is wasted.

The high voltage electricity is transmitted along overhead lines on pylons and through underground cables - the supergrid. But this high voltage is no good to consumers so it is reduced by step down transformers to an appropriate level for the end user - higher voltages for factories, car garages etc. than for homes and offices.

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1.
The electricity generated at power stations is usually at 25,000 V. Which type of transformer is used to change the voltage required by the supergrid?
Step-in
Step-out
Step-up
Step-down
You can remember this because the voltage is increased from the power station to the National Grid (it is 'stepped up')
2.
The National Grid is a system of what?
A system of cables
A system of cables and transformers
A system of cables, transformers and power stations
A system of cables, transformers, power stations and consumers
The transformers change the voltage of the electricity in the National Grid. Power stations and consumers are at either end of the National Grid but not parts of it
3.
Where would you find a step-down transformer?
Near to the power station
In an electricity substation near to the consumers
Part way along the power cables of the National Grid
In people's homes
They are used to reduce the high voltages of the National Grid ready to distribute to consumers
4.
When the National Grid was established, the cables were all carried by pylons. Now, some of the cables of the supergrid have been buried underground. Which of the following is not an advantage of buried high voltage cables?
Underground cables lose less energy
Underground cables are less likely to be damaged or broken in bad weather
Underground cables are more expensive to install
Underground cables have lower maintenance costs
Some people believe that living near overhead power cables causes health issues because of the electromagnetic fields they emit. Underground cables do not emit electromagnetic fields
5.
Which of the following is not an advantage of the National Grid?
Electricity is available at a standard voltage throughout Britain
If a power station breaks down, others can increase output to compensate
It makes electricity much cheaper
Sudden increased demands in electricity can be met
The grid is about having a reliable system that can cope with sudden demands or power station breakdowns without consumers having a power cut. Having a National Grid does not make electricity costs any cheaper
6.
Why are CHP (combined heat and power) stations more efficient than most fossil fuel burning power stations?
They use the heat to heat local buildings as well as to generate electricity
They are more modern
They are a lot smaller
They are run by local businesses so they have to be more efficient to make them more profit
The electricity from CHP stations is usually used locally too. This also makes them more efficient as it avoids the inevitable losses caused by transporting electricity for hundreds of miles
7.
About seven to eight percent of the electrical energy is lost in the National Grid, mainly as which type of energy?
Thermal energy
Light energy
Sound energy
Kinetic energy
When electricity passes through any wire there is a slight resistance. This causes some of the electrical energy to be transferred into heat energy
8.
Which of the following contains the missing words from the passage in the correct order?

________ transformers are used at power stations to produce the very high ____________ needed to ensure that electricity is transmitted efficiently through the National Grid. Such high voltages are dangerous to use in the home, so _________ transformers are used in substations near to homes to reduce the voltage to safe levels. The voltage of ________ electricity is about 230 V.
Step-up, voltages, step-down, household
Large, current, small, safe
Step-up, current, step-down, safe
Step-down, voltages, step-up, factory
If you associate step-up transformers with power stations, that narrows your choice to two possibilities
9.
Which of the following would be a good stand-by power station?
Coal fired power station
Pumped storage hydroelectric power station
Wind turbines
All of the above
You need a power station with a very short start up time that will definitely be available at times of peak electricity demand
10.
Why is electricity carried by the supergrid at very high voltage?
It is a legal requirement
That is the voltage that power station generators produce
It wastes less energy
At lower voltages, it would not have the power to go all over the country
The higher voltages mean lower currents are flowing so less energy is wasted

 

Author:  Kev Woodward

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