Describe direct current (d.c.) as movement of charge in one direction only…

The idea

Direct current means charge flows round the circuit in one direction only; the current does not reverse. Cells and batteries are the everyday sources that supply this one-way current, so a simple series circuit with a battery has charge drifting the same way throughout. To describe d.c., say that the charge movement keeps a single direction, and to recall the source, name cells and batteries. A helpful check is to picture the current–time graph: for steady d.c. it is a flat line above (or below) zero, never crossing the axis, unlike alternating current which reverses.

What earns the marks

• Describes direct current as the movement of charge in one direction only.
• States that the current does not reverse direction in a d.c. circuit.
• Recalls that cells supply direct current.
• Recalls that batteries supply direct current.

Common mistakes and how to put them right

• Says charge moves in both directions in a d.c. circuit.

  Put it right by stating that d.c. charge flow is one way only.

• Names the mains supply as a source of direct current.

  Put it right by recalling that cells and batteries supply d.c.

• Describes d.c. only as a steady size of current without mentioning direction.

  Put it right: Add that the direction of charge movement stays the same.

Exam tips

• Look for the phrase one direction only when judging an option about d.c.
• Match each source to its current type, linking cells and batteries to d.c.
• Reject any option that says the current reverses, because that describes alternating current.