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Magnetism and Electromagnetism

Transformer power, and using the transformer equations

  • 3 things to know
  • Paper 2

Overview

Which coil gives the input and output power, why the current falls when the potential difference rises, how the alternating current in one coil induces a current in the other, and calculations for transmission.

What you need to know

Answer each one before you reveal it.

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Key term

Which coil's potential difference and current give the power output of a transformer?

Key term

Which coil's potential difference and current give the power input of a transformer?

Numbers

A transformer draws a current of 2.0 A from a 230 V supply. Calculate the power input.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Write the equation linking the potential differences and currents in the two coils of a transformer that wastes no energy.

    Model answer

    Vs × Is = Vp × Ip, where p labels the primary coil and s the secondary coil.

  2. 2

    What does the potential difference across a transformer coil multiplied by the current in it tell you?

    Model answer

    The electrical power transferred by that coil.

  3. 3

    Which coil's potential difference and current give the power output of a transformer?

    Model answer

    The secondary coil's.

  4. 4

    Which coil's potential difference and current give the power input of a transformer?

    Model answer

    The primary coil's.

  5. 5

    A transformer draws a current of 2.0 A from a 230 V supply. Calculate the power input.

    Model answer

    Power input = 230 × 2.0 = 460 W.

  6. 6

    In what unit are the input and output powers of a transformer measured?

    Model answer

    In watts, W.

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