Electricity and Magnetism >
Magnetic Materials >
Ferromagnetism
DCS# 5G20.10
BARKHAUSEN EFFECT
APPARATUS
two coils
101-11-E6
iron nail, nickel wire,
paper
clip, copper wire
202-20-B2
amplifier/speaker
202-20-B2
magnet
202-20-B2
DESCRIPTION
An iron nail is placed in a
coil
connected to the amplifier and speaker. Bring the magnet
near the
end of the nail and crackling noises can be heard as magnetic
domains
within the iron shift. The changing magnetic flux from
the
shifting domains induces a signal in the coil which is
amplified and
sent to the speaker. The crackling can also be heard if
the iron
is replaced with a steel paper clip or a piece of nickel
wire. No
noise is heard when a non-ferromagnetic material, e.g. a
copper wire,
or no material at all is used.
NOTES
Use two coils wound in opposite
directions wired together to minimize 60 Hz noise, so the
volume can be
turned up.
