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```					Advanced Higher Physics

Inductors & Inductance
Magnetic Flux

   Magnetic flux, , is a measure of the magnetism in
an area, given by –
=BA

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
d
dt
   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

   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.

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Jun Wang Dr
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