Pearson Edexcel International GCSE (9–1) · PHYSICS · Chapter
Electromagnetism
68 practice questions
Topics covered
Practice questions
21–30 of 35 · Normal
Question 21
3 marks · Normal
Answer and see the solution →A student investigates transformers using different numbers of turns on the secondary coil, measuring output voltages. Her results:
Transformer investigation results Turns on Secondary Coil Output Voltage (V) 100 4.0 200 8.1 300 12.0 400 15.8 (a)[1 mark]Describe the relationship between the number of turns on the secondary coil and the output voltage.
(b)[2 marks]Estimate the output voltage if the secondary coil had 500 turns.
Question 22
4 marks · Normal
Answer and see the solution →A transformer is used to power a device that needs 6 V a.c. from the mains (230 V a.c.). The current in the primary coil is 0.10 A. Assume the transformer is 100% efficient.
(a)[3 marks]Calculate the current in the secondary coil.
(b)[1 mark]Explain why the secondary current is greater than the primary current.
Question 23
3 marks · Normal
Answer and see the solution →Describe two reasons why thick, insulated copper wire and a plastic-coated soft iron core are used in transformer construction.
Question 24
4 marks · Normal
Answer and see the solution →The diagram below shows part of a National Grid system used to distribute electricity from a power station to homes.
A simplified National Grid: Power Station, Step-up Transformer, Transmission lines, Step-down Transformer, Homes. (a)[2 marks]Explain why step-up transformers are used after the power station before transmission.
(b)[2 marks]Explain why step-down transformers are used near homes before the electricity enters houses.
Question 25
4 marks · Normal
Answer and see the solution →A step-up transformer in the National Grid has 120 turns on its primary coil and 6,000 turns on its secondary coil. The primary coil is connected to an alternating voltage of 8 V.
(a)[3 marks]Calculate the voltage across the secondary coil.
(b)[1 mark]Explain whether this transformer increases or decreases the current in the secondary coil compared to the primary coil, assuming 100% efficiency.
Question 26
2 marks · Normal
Answer and see the solution →Give two reasons why high voltages are dangerous in the National Grid and must be reduced before entering homes.
Question 27
3 marks · Normal
Answer and see the solution →The table shows information about two types of transformers.
Transformer data Type of transformer Number of primary turns Number of secondary turns Use in National Grid X 300 9000 Y 4000 200 Complete the table by stating the use of each transformer in the National Grid: either 'step-up' or 'step-down'.
Question 28
4 marks · Normal
Answer and see the solution →Electricity is transmitted over long distances from power stations to towns.
Explain in detail, using scientific ideas about current and voltage, how transformers help to reduce energy loss during this transmission.
(a)[2 marks]Describe what happens to the current in the transmission wires when a step-up transformer increases the voltage.
(b)[2 marks]Explain why this change in current is important for energy loss.
Question 29
4 marks · Normal
Answer and see the solution →A village receives electricity from a National Grid. The voltage on the transmission cables is 132,000 V.
(a)[2 marks]Give two reasons why a step-down transformer is needed before the electricity enters homes.
(b)[2 marks]The step-down transformer reduces the voltage to 230 V. Explain what happens to the current in the secondary coil compared to the primary coil, assuming no energy is lost.
Question 30
3 marks · Normal
Answer and see the solution →Explain, using scientific ideas, why it would be inefficient and impractical to transmit electricity at low voltage but high current.