Pearson Edexcel International GCSE (9–1) · PHYSICS · Chapter
Electromagnetic Induction
61 practice questions
Topics covered
Practice questions
31–37 of 37 · Normal
Question 31
4 marks · Normal
Answer and see the solution →The table below shows the number of turns and voltage in different parts of a section of the National Grid:
Transformer Primary coil turns Secondary coil turns Primary voltage (V) Secondary voltage (V) Step-up 500 10,000 20 Step-down 2,000 200 220 (a)[2 marks]Calculate the output (secondary) voltage of the step-up transformer.
(b)[2 marks]Calculate the input (primary) voltage of the step-down transformer.
Question 32
4 marks · Normal
Answer and see the solution →A simplified diagram representing a section of the National Grid is shown below.
National Grid section (Power station, Step-up transformer, Transmission line, Step-down transformer, Factory) (a)[2 marks]On the diagram, draw and label the sections where the voltage is highest and lowest.
(b)[2 marks]Explain, using the diagram, why a step-down transformer is used before electricity enters a factory.
Question 33
3 marks · Normal
Answer and see the solution →Explain what would happen if only step-up transformers (no step-down transformers) were used in the National Grid. Give two consequences for users and one for the safety of the system.
Question 34
1 mark · Normal
Answer and check →Which statement about transformers in the National Grid is correct?
- A.Step-up transformers increase voltage and reduce current for transmission.
- B.Step-down transformers increase voltage before transmission.
- C.Step-up transformers are only used in homes.
- D.Step-down transformers are used to increase voltage to dangerous levels.
Question 35
6 marks · Normal
Answer and see the solution →A small wind turbine uses a generator to produce electricity for charging batteries in a remote location. The generator works by spinning a coil inside a magnetic field.
(a)[1 mark]State what is meant by electromagnetic induction in this context.
(b)[2 marks]List two ways, other than increasing the strength of the magnets, that the voltage produced by the generator can be increased?
(c)[1 mark]The voltage output from the generator is too low to charge the batteries efficiently. An engineer suggests using a transformer. The transformer has 60 turns on the primary coil and 240 turns on the secondary coil. The generator provides an input of 9 V a.c.
(d)[2 marks]Explain why a transformer cannot be used if the generator produced direct current (d.c.) instead of alternating current (a.c.).
Question 36
6 marks · Normal
Answer and see the solution →Mains electricity is transmitted over large distances from power stations to towns and cities using the National Grid system. Step-up and step-down transformers are used at different stages.
(a)[2 marks]Explain why step-up transformers are used before electrical energy is transmitted on the National Grid.
(b)[2 marks]A step-up transformer has 500 turns on its primary coil and 15,000 turns on its secondary coil. The input voltage is 2,500 V a.c. Calculate the output voltage.
(c)[2 marks]Before the electricity reaches homes, it passes through a step-down transformer. State the purpose of the step-down transformer, and give a typical output voltage for domestic use.
Question 37
4 marks · Normal
Answer and see the solution →A power station supplies 20,000 V a.c. at a current of 800 A to a step-up transformer which is 100% efficient. The transformer increases the voltage for long-distance transmission. A second transformer later steps the voltage down to 5,000 V for use in a factory.
(a)[2 marks]Calculate the output current from the step-up transformer if the transmission voltage is increased to 100,000 V.
(b)[2 marks]Calculate the current supplied to the factory after the voltage is stepped down to 5,000 V, assuming 100% efficiency throughout.