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Advanced Higher Physics
Electromagnetic Induction
Magnetic Flux

Magnetic flux, , is a measure of the magnetism in
an area, given by –
=BA
where -
BA–
magnetic flux (Wb)
magnetic induction (T)
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
d
e
dt
(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.
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 pickups
As the strings vibrate, the
magnetic field of the pickup 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.