Explain how a current-carrying wire placed in a magnetic field experiences a force, and state two factors that would increase the size of this force.

Eduqas GCSE Physics — 8.2 Magnetic effects of currents and the motor effect · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

A current‑carrying wire has its own magnetic field around it. This magnetic field interacts with the external magnetic field, producing a force on the wire (the motor effect). The force increases if the current is increased, and it also increases if the strength of the external magnetic field is increased.

Examiner tips

Use the phrase "motor effect" to show understanding of the interaction of magnetic fields.
Show the two factors (current and magnetic field strength) explicitly and explain why each increases the force.
Keep the answer concise – 4 marks are enough for a short explanation.
Use UK spelling (e.g. "magnetic field strength").

Common mistakes

Failing to mention that the wire’s own magnetic field interacts with the external field.
Only naming one factor (e.g. current) and omitting the second (magnetic field strength).
Using vague wording such as "more current" without linking it to the force equation.

Mark scheme (4 marks)

The current-carrying wire has its own magnetic field around it
This magnetic field interacts with the external magnetic field
One correct factor that increases the force — increasing the current
A second correct factor that increases the force — increasing the magnetic field strength

Key terms in this question

magnetic field · current · force

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