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Magnetic Fields

Faraday's law of electromagnetic induction

  • 3 things to know
  • Unit A2 2

Overview

Faraday's law of electromagnetic induction, three ways of inducing an e and experiment demonstrating Faraday's law.

What you need to know

Answer each one before you reveal it.

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Key term

State Faraday's law of electromagnetic induction.

Key term

Describe an experiment demonstrating Faraday's law.

Key term

In a demonstration of Faraday's law, what is observed when the magnet is withdrawn from the coil instead of pushed in?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    State Faraday's law of electromagnetic induction.

    Model answer

    The magnitude of the induced electromotive force is proportional to the rate of change of magnetic flux linkage.

  2. 2

    Give the equation for the average induced e.m.f. and define each symbol.

    Model answer

    E = −Δ(Nφ)/Δt, where E is the induced e.m.f. in volts, Δ(Nφ) the change in flux linkage in weber-turns and Δt the time taken in seconds.

  3. 3

    Name three ways of inducing an e.m.f. in a coil.

    Model answer

    Moving a magnet into or out of the coil, moving the coil in a field, and changing the current in a nearby coil so the field through this one changes.

  4. 4

    Why is no e.m.f. induced when a magnet is held stationary inside a coil?

    Model answer

    The flux linkage is not changing, and it is the rate of change and not the value of the flux that induces an e.m.f.

  5. 5

    Describe an experiment demonstrating Faraday's law.

    Model answer

    A bar magnet is pushed into a coil connected to a sensitive centre-zero galvanometer, and the meter deflects while the magnet moves and returns to zero when it stops.

  6. 6

    What is observed when the magnet is withdrawn instead?

    Model answer

    The meter deflects in the opposite direction, because the flux linkage is now decreasing rather than increasing.

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