Lesson 3.7.5.6

3.7.5.6 The operation of a transformer Quiz: AQA Physics, Unit 7

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.7.5.6, The operation of a transformer: 20 multiple choice questions for the AQA Physics (7408), Unit 7: Fields and their consequences (A-level only), written with Revision Ninja.

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The 20 questions

  1. Which equation correctly links transformer coil turns and voltages?

    • Vs / Vp = Ns / Np
    • Vs - Vp = Ns - Np
    • Vs * Vp = Ns * Np
    • Vs / Vp = Np / Ns

  2. Which expression gives the efficiency of a transformer in terms of currents and voltages?

    • (Is Vp) / (Ip Vs)
    • (Is Vs) / (Ip Vp)
    • (Ip Is) / (Vp Vs)
    • (Ip Vp) / (Is Vs)

  3. Why is the iron core of a transformer laminated?

    • Prevent flux leakage
    • Reduce eddy currents
    • Increase magnetic flux
    • Reduce wire resistance

  4. Which effect causes heating in the iron core of a transformer?

    • Flux leakage
    • Eddy currents
    • Winding resistance
    • Diode rectification

  5. A step-down transformer has 1000 primary turns and 100 secondary turns. The primary is supplied at 230 V. What is the secondary voltage?

    • 230 V
    • 10 V
    • 23 V
    • 2300 V

  6. A step-up transformer must raise 12 V to 240 V. If the primary has 60 turns, how many secondary turns are needed?

    • 60 turns
    • 240 turns
    • 1200 turns
    • 600 turns

  7. A transformer has an input power of 100 W and an output power of 90 W. What is its efficiency?

    • 100%
    • 9%
    • 90%
    • 10%

  8. A transformer draws 115 W from the mains and delivers 100 W to its load. What is its efficiency?

    • 100%
    • 50%
    • 115%
    • 87%

  9. An ideal step-down transformer has a primary voltage of 240 V and a primary current of 2.0 A. Its secondary voltage is 12 V. What is the secondary current?

    • 0.10 A
    • 2.0 A
    • 40 A
    • 20 A

  10. A transmission line carries 100 kW at 10 kV and has a total resistance of 5.0 ohm. What is the power lost in the line?

    • 5 kW
    • 500 W
    • 5 W
    • 50 kW

  11. Power transmission voltage increases by a factor of 10. By what factor do power losses change?

    • 100 times larger
    • 10 times smaller
    • 100 times smaller
    • 10 times larger

  12. 1.0 MW is transmitted at 25 kV through a line of resistance 2.0 ohm. What is the power lost in the line?

    • 3.2 kW
    • 40 kW
    • 80 kW
    • 0.32 kW

  13. A transformer has 500 primary turns and is supplied at 230 V. What number of secondary turns gives 10 V?

    • 435 turns
    • 11 turns
    • 2300 turns
    • 22 turns

  14. Why is electricity transmitted across the National Grid at very high voltage?

    • Prevents power surges
    • Reduces cable resistance
    • Reduces thermal losses
    • Increases current speed

  15. A transformer is 80% efficient. Its primary draws 2.0 A at 230 V. What output power does it deliver?

    • 460 W
    • 368 W
    • 575 W
    • 92 W

  16. Which feature of a transformer core minimises energy loss due to eddy currents?

    • Laminated structure
    • Air gap core
    • Thicker iron plates
    • High-resistance copper

  17. A transformer with a secondary-to-primary turns ratio of 0.5 is supplied at 230 V. What is the secondary voltage?

    • 230 V
    • 57.5 V
    • 115 V
    • 460 V

  18. A transformer delivers 12 V at 3.0 A from a 230 V primary drawing 0.18 A. What is its efficiency?

    • 0.15%
    • 100%
    • 87%
    • 67%

  19. Why does a transformer fail to operate with a steady direct current?

    • No changing flux
    • Zero primary voltage
    • Zero core magnetisation
    • Constant low resistance

  20. A transformer has 1500 primary turns and 500 secondary turns, with 230 V on the primary and 0.50 A in the primary. Ignoring losses, what is the secondary current?

    • 4.5 A
    • 0.17 A
    • 1.5 A
    • 0.50 A

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