Y9 Physics - Electromagnetism + Motor effect

Current carrying wire magnetic field

When electric current flows through a wire, it produces a magnetic field around it because moving charges generate magnetic fields

Magnetic field shape around wire

The field forms concentric circles centred on the wire

Right hand rule

A rule to find field direction where the thumb shows current direction and curled fingers show magnetic field direction

Magnetic field strength (wire)

Increases with current and decreases with distance from the wire

Solenoid

A long coil of wire that produces a magnetic field when current flows through it

Why solenoids are stronger

Each loop’s magnetic field adds together, creating a strong and uniform field inside

Solenoid field shape

Similar to a bar magnet with distinct north and south poles

Increase solenoid strength

Increase current, increase turns per metre, or add an iron core

Iron core effect

The iron becomes an induced magnet and its aligned domains strengthen the magnetic field

Electromagnet

A solenoid with an iron core that produces a controllable magnetic field when current flows

Electromagnet advantages

Can be switched on or off and have adjustable strength

Motor effect

A force experienced by a current

Cause of motor effect

The magnetic field around the wire interacts with the external magnetic field, producing a sideways force

Fleming’s left

hand rule

Force direction principle

The force is always perpendicular to both the magnetic field and the current

Force equation

The force on a wire in a magnetic field depends on magnetic flux density, current, and length of wire

Force equation meaning

Greater magnetic field strength, current, or wire length increases the force

Magnetic flux density

A measure of magnetic field strength in teslas (T)

Motor structure

A coil of wire placed in a magnetic field that carries current

Motor turning effect

Opposite forces act on each side of the coil, creating a turning effect (moment)

Motor rotation

The coil rotates because forces act in opposite directions on either side

Commutator (split ring)

Reverses current every half

Why commutator is needed

Without it, the coil would stop after half a turn

Electric motor

A device that uses the motor effect to convert electrical energy into kinetic energy

Loudspeaker principle

Uses the motor effect to convert electrical signals into sound waves

Loudspeaker coil

A coil in a magnetic field that moves when current flows

Effect of alternating current

The changing direction of current causes the force to change direction, making the coil vibrate

Sound production

Vibrations of the coil move a cone which vibrates air to produce sound waves

Why AC is used

Alternating current continuously reverses direction, producing repeated vibrations needed for sound

Motor effect applications

Used in electric motors, loudspeakers, headphones, and many electrical devices