ENERGY IN TRANSFORMERS
2 marks · NormalA student suggests using a transformer with a direct current (d.c.) supply.
Explain why a transformer does not work with d.c.
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A transformer needs a changing magnetic field, which only occurs with a.c.; d.c. produces a constant field so no voltage is induced in the secondary coil.
Also accept: Transformer only works with a.c. because d.c. does not create a changing magnetic field
Common mistakes: Saying 'd.c. does not work' without explanation
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Marking points
M1 (a) · 1 mark · States transformers need a changing (alternating) magnetic field.
A1 (a) · 1 mark · Explains d.c. produces a constant field, so no voltage is induced.
Worked solution
A transformer works by a changing magnetic field, produced by alternating current. D.C. gives a steady magnetic field, so no voltage is induced in the secondary coil.