Download P1 4.5 Questions and answers File

P1 4.5 – Questions and answers
1 Why is the voltage increased before electricity is sent
through the National Grid?
A Increasing voltage reduces the current, which reduces the
amount of energy wasted as heat.
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P1 4.5 – Questions and answers
2 Why is the voltage then reduced before electricity is
supplied to homes?
A Lower voltages are safer.
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P1 4.5 – Questions and answers
3 Look at Figure 1. The transformers are labelled A–D. For
each transformer, say whether it is a step-up or step-down
transformer.
A A is a step-up transformer; the others are all step-down
transformers.
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P1 4.5 – Questions and answers
4 Which of these electricity supplies provides the most power:
2 A at 230 V or 18 A at 20 V? Explain your answer.
A 2 A at 230 V (this provides 460 W while 18 A at 20 V provides
360 W).
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P1 4.5 – Questions and answers
5 A step-down transformer halves the voltages of the
electricity supplies in question 4. What will the new currents
be?
A Double the values given: 4 A and 36 A.
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P1 4.5 – Questions and answers
6 An advert for solar cells claims that any electricity that the
homeowner does not use can be sold to the National Grid.
Explain why this claim is not entirely correct.
A If a house is not already connected to the National Grid
(because it is in a remote location), it may not be economic
to connect it; electricity cannot be sold if there is no
connection.
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P1 4.5 – Questions and answers
7 What are the advantages and disadvantages of burying
power cables underground?
A Advantages: does not cause visual pollution, protected from
the weather; disadvantages: more insulation is needed, it is
more expensive to install, and it is harder to find faults.
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P1 4.5 – Questions and answers
8 Explain why the following statement is partly correct and
partly incorrect: ‘A step-up transformer increases the energy
provided by the electricity supply.’ Use data from Figure 1 to
support your answer.
A A step-up transformer increases the voltage of the supply,
and reduces the current. The amount of energy wasted as
heat depends on the current, so by increasing the voltage
the transformer has reduced wasted energy and so
increased the amount of energy that is usable. However,
the total energy (including wasted energy) remains the
same because the power (energy per second) depends on
both current and voltage.
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copyright free. This document may have been altered from the original.