68. Generator Effect / Electromagnetic Induction

An electric motor uses the motor effect to convert electrical energy into kinetic energy (rotational motion).

1. The Core Principle

When a current-carrying wire is placed in a magnetic field, it experiences a force. In a simple motor, we use a rectangular coil of wire that is free to rotate in a magnetic field.

• Opposing Forces: Because the current flows in opposite directions on each side of the coil, one side experiences an upwards force while the other experiences a downwards force.

• Rotation: These two opposing forces act as a couple, causing the coil to spin.

2. The Split-Ring Commutator

If the coil were simply connected to a battery, it would only rotate 180° before the forces swapped direction and pushed it back the other way. To keep the motor spinning in the same direction, we use a split-ring commutator.

• How it Works: The commutator acts as a rotating switch. It swaps the positive and negative connections to the coil every half-turn (-180°).

• Result: This reverses the direction of the current through the coil every half-turn, ensuring the forces always act in a way that maintains continuous rotation in one direction.

3. Increasing the Motor's Speed

There are three main ways to increase the speed of rotation or the strength of an electric motor:

1. Increase the Current: Provide more electrical power to the circuit.

2. Add More Turns to the Coil: Increase the number of loops of wire in the magnetic field.

3. Use Stronger Magnets: Increase the magnetic flux density of the surrounding field.

4. Summary Table

5. Applications

The electric motor is a fundamental piece of technology found in:

• Electric vehicles

• Fans and hair dryers

• Hard drives and appliances