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Electric and Magnetic Fields

The conditions for inducing an e.m.f.

  • 3 things to know
  • Papers 1 and 3

Overview

Recall questions on what must change for an e.m.f. to be induced, the three factors that set its size, why a steady current induces nothing, and the effect of an iron core.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Process

What condition is necessary for an e.m.f. to be induced in a coil?

Process

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

Process

Why does adding a soft iron core increase the e.m.f. induced in a linked coil?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    What condition is necessary for an e.m.f. to be induced in a coil?

    Model answer

    The flux linkage through the coil must be changing.

  2. 2

    Which three factors affect the size of the e.m.f. induced when a permanent magnet is moved into a coil?

    Model answer

    The speed of the relative motion, the strength of the magnet and the number of turns on the coil.

  3. 3

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

    Model answer

    Because the flux linkage is constant, so its rate of change is zero.

  4. 4

    What happens to the induced e.m.f. if the magnet is pulled out of the coil instead of being pushed in?

    Model answer

    The e.m.f. is induced in the opposite direction, because the flux linkage is now decreasing rather than increasing.

  5. 5

    Why is a larger e.m.f. induced when a magnet is moved into a coil more quickly?

    Model answer

    Because the same change of flux linkage occurs in a shorter time, giving a greater rate of change of flux linkage.

  6. 6

    Which three factors affect the e.m.f. induced in a coil when the current in a second coil linked to it changes?

    Model answer

    The rate at which the current in the first coil changes, the number of turns on each coil and whether a soft iron core links the two coils.

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