Pearson Edexcel International GCSE (9–1) · PHYSICS · Chapter
Electromagnetic Induction
61 practice questions
Topics covered
Practice questions
51–60 of 61
Question 51
3 marks · Normal
Answer and see the solution →A section of the National Grid transmits 2000 kW of electrical power at 400,000 V.
(a)[2 marks]Calculate the current in the transmission line.
(b)[1 mark]Explain why this high voltage is used with reference to energy loss.
Question 52
4 marks · Normal
Answer and see the solution →A transformer used in the National Grid has 200 turns on its primary coil and 4000 turns on its secondary coil. The input voltage is 5 V a.c.
(a)[3 marks]Calculate the voltage across the secondary coil.
(b)[1 mark]State whether this transformer is a step-up or step-down transformer. Give a reason for your answer.
Question 53
4 marks · Normal
Answer and see the solution →Electricity generated at a power station must travel long distances before it reaches homes and factories.
(a)[2 marks]Describe the effect a step-up transformer has on current and voltage when used in the National Grid.
(b)[2 marks]Explain why using step-up transformers is important for reducing energy losses in transmission lines.
Question 54
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 55
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 56
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 57
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 58
4 marks · Easy
Answer and see the solution →Electricity generated at a power station is transmitted long distances before entering homes.
(a)[2 marks]Explain why a step-up transformer is used before electricity is transmitted through the National Grid.
(b)[2 marks]A step-up transformer increases the voltage from 10,000 V to 100,000 V. If the current in the primary coil is 50 A, and the transformer is 100% efficient, calculate the current in the secondary coil.
Question 59
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 60
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.