Pearson Edexcel International GCSE (9–1) · PHYSICS · Chapter
Electromagnetic Induction
61 practice questions
Topics covered
Practice questions
21–30 of 37 · Normal
Question 21
3 marks · Normal
Answer and see the solution →(a)[1 mark]State the meaning of 100% efficiency in a transformer.
(b)[2 marks]A transformer has an efficiency of 100%. The secondary coil provides an output power of 60 W. What is the input power?
Question 22
3 marks · Normal
Answer and see the solution →Describe two design features that help real transformers approach 100% efficiency. For each feature, briefly explain how it reduces energy losses.
Question 23
1 mark · Normal
Answer and check →A transformer has an input power of 75 W. Assuming 100% efficiency, which one of the following is the output power?
- A.50 W
- B.60 W
- C.75 W
- D.150 W
Question 24
4 marks · Normal
Answer and see the solution →(a)[3 marks]The table below shows input and output voltages and currents for three different transformers, each operating at 100% efficiency. Transformer Vp (V) Ip (A) Vs (V) Is (A) X 120 0.25 12 Y 240 0.15 48 Z 110 1.0 22 Complete the table by calculating the missing output current (Is) for each transformer.
(b)[1 mark]Explain briefly how you calculated the output current for transformer X.
Question 25
3 marks · Normal
Answer and see the solution →A transformer used in a mobile phone charger has an input voltage of 220 V and input current of 0.05 A. If the transformer is 100% efficient and the output power required is 8.8 W, what is the output current?
Question 26
2 marks · Normal
Answer and see the solution →State one purpose of a step-up transformer and one purpose of a step-down transformer in the National Grid.
Question 27
4 marks · Normal
Answer and see the solution →The diagram shows a simplified section of the National Grid.
National Grid: transformers and cables (a)[2 marks]Explain why a step-up transformer is used before electricity enters the transmission line.
(b)[2 marks]Explain why a step-down transformer is needed before electricity is supplied to consumers.
Question 28
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 29
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 30
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.