ALTERNATING CURRENT AND DIRECT CURRENT

2 marks · Normal

Describe two differences between the current from a cell and the current from the mains electricity supply.

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1. Current from a cell is direct current (d.c.) and flows in only one direction with constant value. 2. Current from the mains is alternating current (a.c.) and regularly changes direction and size.

Also accept: d.c. is produced by cells; a.c. is produced by mains; also accept mention of frequency for a.c. if accurate.

Common mistakes: Mixing up the definitions for a.c. and d.c.

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Marking points

B1 · 1 mark · States that current from a cell is direct and flows only in one direction (d.c.).

B2 · 1 mark · States that current from the mains is alternating and regularly reverses direction (a.c.).

Worked solution

1. The current from a cell is direct (d.c.), flowing in only one direction and at a steady value.

2. The current from mains electricity is alternating (a.c.), regularly changing direction and size.