THE TRANSFORMER

2 marks · Easy

State and explain why transformers only work with alternating current (a.c.) and not with direct current (d.c.).

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Transformers only work with a.c. because a changing magnetic field is required to induce a voltage in the secondary coil. D.c. does not produce a changing magnetic field, so no voltage is induced.

Also accept: Transformers work with a.c. because a changing magnetic field is needed to induce a voltage; d.c. produces a steady field so nothing is induced.

Common mistakes: Saying transformers work equally well with d.c.; Leaving out idea of changing magnetic field

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Marking points

B1 · 1 mark · States that transformers require a changing magnetic field.

B2 · 1 mark · States that a.c. provides a changing field, d.c. does not/only produces a steady field.

Worked solution

Transformers work by using a changing magnetic field to induce a voltage in the secondary coil.

Alternating current (a.c.) produces a changing magnetic field, but direct current (d.c.) only produces a steady magnetic field, so no voltage is induced in the secondary coil with d.c.