Q6 — How a d.c. motor works (6 marks)

Explain how a simple d.c. motor uses the motor effect to produce continuous rotation. Refer to the role of the split-ring commutator in your answer. (6 marks)

Mark scheme — level-marked, indicative content:

• Current passes through a coil placed in a magnetic field (1)
• Each side of the coil carries current in opposite directions (1)
• By Fleming's left-hand rule, one side experiences an upward force, the other a downward force (1)
• This produces a turning effect / couple / torque on the coil (1)
• As the coil passes the vertical, the split-ring commutator reverses the current in the coil (1)
• This ensures the force on each side keeps pushing the coil in the same direction, giving continuous rotation (1)

Levels:

• 5–6: clear, logical, uses correct terminology, links commutator action to continuous rotation.
• 3–4: some correct physics but incomplete or muddled link to commutator.
• 1–2: isolated correct facts only.
• 0: no relevant physics.