What does an electric motor do?

Electric motors use electricity to create rotational motion.


This is because a coil of wire carrying a current, placed in a magnetic field, rotates due to the motor effect.

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Name the device labelled A in the above diagram.

Split-ring commutator.

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How does a split ring commutator ensure the coil rotates in one direction?

  1. The split-ring commutator swaps the positive and negative connections every half turn, meaning the direction of the current through the coil reverses every half turn.
  2. This means that the forces acting on the coil will always be acting in the same direction.
  3. This causes the coil to rotate continuously in one direction.

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Give 4 ways to increase the speed of rotation in an electric motor.

  1. Increase the current in the coil.
  2. Add more turns to the coil.
  3. Use stronger magnets.
  4. Add a soft iron core to the coil.

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What is the motor effect?

The motor effect is the phenomenon that when a conductor carrying a current is placed in a magnetic field, the magnet producing the field and the conductor will exert a force on each other. 

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When will a wire carrying a current experience a larger force: when it is parallel to the magnetic field, or perpendicular to the magnetic field?

To experience the full force, a current-carrying wire must be placed perpendicular to the magnetic field.

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What is Fleming's left hand rule?

Flemings left hand rule is a technique used to figure out the direction of the force experienced by a current carrying wire in a magnetic field.

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What is the formula linking force (F), current (I), magnetic flux density (B), length of conductor (l), and the angle between the conductor and the field (θ\theta) ?

F = BIl sin(θ)


F = force (N)

B = magnetic flux density (T)

I = current (A)

l = length (m)

θ\theta = angle between conductor and field (°) 

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