Advanced Higher Physics

Inductors & Inductance

Magnetic Flux

Magnetic flux, , is a measure of the magnetism in an area, given by –

= B A

where - - magnetic flux (Wb)

B - magnetic induction (T)

A – area perpendicular to magnetic field lines (m2)

Solenoids 1

A coil carrying an electrical current is known as a solenoid.

The current induces a magnetic field in the coil

The direction of the field is determined by the direction of the current in the coil.

Induced EMF 1

Any conductor contains ‘free electrons’

When moving within a magnetic field individual electrons in a conductor experience a force, F = B I l sin, causing them to move

This results in an induced EMF.

Motion is relative – conductor in field or field past conductor.

Induced EMF 2

SCHOLAR DEMO

Size of induced EMF relates to –

Speed of motion Direction of motion No. of turns on coil

EMF is caused by changing magnetic flux

Induced EMF 3

Magnitude of EMF is related to rate of change of magnetic flux

(Faraday’s Law)

If the magnetic field strength is changing, an EMF is induced in a conductor placed in the field.

So an EMF can be induced by changing the strength of a magnetic field without needing to physically move a magnet or a conductor.

dt

de

Uses of Magnetic Induction 1

Video & audio cassette players, hard drives are magnetic media.

Information is recorded onto a magnetic tape or disc, which passes a coil with an iron core (reading head), inducing a current.

The current provides the signal required for the system

Uses of Magnetic Induction 2

Electric guitars use steel strings and magnetic pick-ups

As the strings vibrate, the magnetic field of the pick-up changes

A coil wrapped around the magnet has a current induced, producing a signal

The signal is amplified and sent to a loudspeaker

Uses of Magnetic Induction 3

Microphones have a diaphragm connected to a coil which moves within a magnetic field

Sound wave cause the diaphragm and coil to vibrate inside the magnetic field, inducing a current.

The signal is amplified and sent to a loudspeaker.