Alternating current and direct current

2 marks · Easy

Explain the difference between the voltage graph of an alternating current (a.c.) and a direct current (d.c.) supply.

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Also accept: a.c. voltage changes direction and size repeatedly over time; d.c. voltage stays constant and does not change direction

Common mistakes: Only describing one type (a.c. or d.c.), not both

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Marking points

B1 · 1 mark · States that a.c. voltage changes repeatedly (alternates)

B1 · 1 mark · States that d.c. voltage is constant (does not alternate)

Worked solution

In an a.c. supply, the voltage rises and falls, changing direction repeatedly, forming a wave on a graph. In a d.c. supply, the voltage stays at a constant value with no change in direction; the graph would be a straight horizontal line.