Alternating current and direct current

2 marks · Normal

State the main difference between alternating current (a.c.) and direct current (d.c.). Give one example of each.

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A.c. reverses direction periodically; d.c. flows in one direction only. Example of a.c.: mains electricity. Example of d.c.: battery.

Also accept: A.c. changes direction, d.c. is steady and one way. A.c. = mains, d.c. = cell.

Common mistakes: Describing a.c. as just 'stronger' or 'weaker' instead of changing direction

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Marking points

B1 · 1 mark · Correct difference stated (a.c. reverses direction; d.c. flows in one direction only)

B2 · 1 mark · One example for each (a.c. = mains, d.c. = battery/cell)

Worked solution

Alternating current (a.c.) changes direction regularly, while direct current (d.c.) flows only in one direction. An example of a.c. is mains electricity; an example of d.c. is the current from a battery.