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Electromagnetic Induction

How a transformer works

  • 3 things to know
  • Paper 2

Overview

The construction of a transformer, how an alternating current in the primary coil induces a potential difference in the secondary, why direct current gives no output, the soft iron core, and step-up and step-down transformers and their turns.

What you need to know

Answer each one before you reveal it.

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Key term

Describe the basic construction of a transformer.

Key term

Explain why a transformer produces no output when a steady direct current flows in its primary coil.

Key term

Explain why the two coils of a transformer can be electrically insulated from each other and still transfer energy.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Describe the basic construction of a transformer.

    Model answer

    Two coils of insulated wire, called the primary and the secondary, are wound on a core of soft iron.

  2. 2

    Explain how an alternating current in the primary coil of a transformer induces a potential difference in the secondary coil.

    Model answer

    The alternating current creates a continually changing magnetic field in the core, and that changing field induces a potential difference in the secondary coil.

  3. 3

    Explain why a transformer produces no output when a steady direct current flows in its primary coil.

    Model answer

    A steady current gives an unchanging magnetic field, and only a changing field can induce a potential difference.

  4. 4

    State the purpose of the iron core in a transformer.

    Model answer

    It carries the changing magnetic field from the primary coil across to the secondary coil.

  5. 5

    Explain why the two coils of a transformer can be electrically insulated from each other and still transfer energy.

    Model answer

    The energy is carried between them by the changing magnetic field, not by charge flowing from one coil to the other.

  6. 6

    Name the coil of a transformer that is connected to the input supply.

    Model answer

    The primary coil.

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