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 is the transformer equation for an ideal transformer?

    • Vs / Vp = Ns / Np
    • Is / Ip = Ns / Np
    • Vs x Ns = Vp x Np + Is
    • Vs / Vp = Np / Ns

  2. Which expression gives the efficiency of a transformer?

    • efficiency = (Ip x Vp) / (Is x Vs)
    • efficiency = (Is x Vs) / (Ip x Vp)
    • efficiency = (Is x Vs) / (Ip x Vs)
    • efficiency = (Is x Vp) / (Ip x Vs)

  3. Why is the core of a transformer laminated?

    • Laminations make the core stronger against mechanical vibration
    • Laminations reduce the size of eddy currents and so reduce heating losses in the core
    • Laminations increase the flux linkage in each turn of the windings
    • Laminations stop the magnetic field leaking out of the transformer

  4. Which is a cause of energy loss in a practical transformer?

    • air resistance acting on the moving coils
    • eddy currents and resistance in the windings, together with magnetic flux leakage
    • friction in the bearings supporting the core
    • the secondary voltage rising above the primary voltage

  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. The same power is sent along the same cables at 400 kV rather than 40 kV. How do the losses compare?

    • 10 times more at 400 kV
    • 10 times less at 400 kV
    • 100 times less at 400 kV
    • 100 times more at 400 kV

  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 at high voltage rather than high current?

    • High voltage insulates the cables so that heat cannot escape
    • High voltage increases the power so less current is needed for the same demand
    • Higher voltage means lower current for the same power, so the I^2 R losses in the cables are smaller
    • Higher voltage means higher current and so less resistance in the cables

  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 change makes the core of a transformer less lossy?

    • using a laminated soft iron core to increase the resistance to eddy currents
    • increasing the frequency of the input supply
    • replacing the iron core with a solid copper core
    • using a solid iron core with thicker windings

  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 not work with a steady direct current in the primary?

    • A steady current gives a constant flux, so no changing flux links the secondary and no emf is induced
    • Direct current flows only through the primary and never reaches the secondary
    • The core becomes permanently magnetised by a steady current
    • Direct current is too high in voltage to pass through the windings

  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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