Electric Motors

Electric motors change electrical energy into movement. They are used in fans, toy cars, drills, and many appliances. The key idea is the motor effect: a current-carrying wire in a magnetic field feels a force.

Key parts of a simple d.c. motor

• Coil (armature): a loop of wire that carries current.
• Magnets: create a magnetic field between North and South poles.
• Split-ring commutator: metal ring cut into two halves, connected to the coil.
• Brushes: pieces of carbon that press on the commutator to supply current from the battery.

How it works

1. Current flows through the coil. One side of the coil has current in one direction; the opposite side has current in the opposite direction.
2. In the magnetic field, each side feels a force in opposite directions. One side is pushed up, the other down, so the coil turns.
3. After half a turn, the split-ring commutator reverses the current in the coil. This keeps the push on each side in the same turning direction, so the coil keeps spinning.

Increasing the turning effect (torque)

• More turns on the coil (increase N)
• Bigger current (increase I)
• Stronger magnetic field (increase B)

Together:

$$\text{Turning effect} \propto N\,I\,B$$

Direction of rotation

Use Fleming’s left-hand rule: hold thumb, first finger, and second finger at right angles. First finger = field (N to S), second finger = current, thumb = force (motion).

Real-world connections

• Fans and hairdryers: small d.c. motors spin blades.
• Electric scooters: larger motors provide more torque for hills.
• Washing machines: control speed by changing current and coil design.

Common misconceptions

• Magnets do not “pull” the coil around. The magnetic field and current create forces on the wire.
• Without a split-ring commutator, the coil would stop every half-turn because the torque would reverse.
• Brushes do not spin with the coil; they stay still and press on the commutator to supply current.