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Physics · 4.5.4 The d.c. motor & motor effect

Motor Effect. Spin it.

A current-carrying conductor in a magnetic field feels a force (the motor effect). In a d.c. motor a coil between magnets experiences a turning effect; the split-ring commutator reverses the current every half-turn to keep it spinning. Use Fleming's left-hand rule to predict the force direction.

0625 Topic 4.5.1 — Motor effect 4.5.1 — d.c. motor Fleming's left-hand rule
d.c. motor — the coil spins; the commutator flips the current each half-turn so the turning effect keeps going one way.

Variables

2.0
1.0
5

Live readouts

Current I
2.0 A
Turning force (relative)
2.0
Force on top wire
upward
Speed
medium
Force increases with current, field strength and number of turns. Reversing current OR field reverses the force / spin direction.
📋 Fleming's left-hand rule & the motor (Cambridge)
  • Fleming's left-hand rule: thuMb = Motion (force), First finger = Field (N→S), seCond finger = Current. Hold them at right angles.
  • The two sides of the coil carry current in opposite directions, so they feel opposite forces — creating a turning effect (a couple).
  • The split-ring commutator reverses the current in the coil every half-turn, so the coil keeps rotating the same way.
  • Increase the turning effect with: a larger current, a stronger magnetic field, more turns on the coil, or a larger coil area.
🎯 Syllabus reference (0625)
  • 4.5.1 Force on a current-carrying conductor — describe the motor effect; use Fleming's left-hand rule; state factors affecting the force; describe a simple d.c. motor including the action of the split-ring commutator.

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