1 induced magnetism

This is in the chapter electric and electromagnetism

1. INDUCED
MAGNETISM
HOW TO MAKE A
MAGNET?

2. Materials
MAGNETIC MATERIALS NON-MAGNETIC MATERIALS
FERROUS NON-FERROUS
Iron Plastic
Nickel Wood
Cobalt Rubber

3. Induced magnetism
The side of the material facing the magnet will become
the opposite pole as the magnet
Aninduced magnetonly becomes amagnetwhen it is
placed in a magnetic field.
Theinduced magnetism is quickly lost when the magnet
is removed from the magnetic field.
The nails in the image become induced magnetswhen
they are near the barmagnet.

4. 2 objects neither are magnetic
materials
Place a permanent magnet in
between.
Magnetic fields… can be seen….hence
materials becomes induced magnets
Methods of inducing magnetism:
Most effective method:
place it in a solenoidand pass a
large, direct current (d.c.) through
the coil.
SN??
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5. Methods of
demagnetisation:
•If a magnet is hammered, its atomic
magnets are thrown out of line, and
it becomes demagnetized.
•Heatinga magnet to a high
temperature also demagnetize it.
•Stroking with another magnet to
destroy the alignment of poles
•Place magnet with poles opposite
to that which is induced by a d.c.
current and insert into coil with d.c.
current
•Most efficient method: place
magnet inside a solenoid
connected to an alternating current
(a.c.) supply

6. Soft iron vs. steel
Soft iron steel
Gets magnetized faster but
loses its magnetism as soon
as inducing magnet is
removed.
Slow to be magnetized but
retains acquired magnetism
for a long time
High susceptibility but low
retentivity
Slow to be magnetized but
retains acquired magnetism
for a long time
High susceptibility but low
retentivity
Use: making magnets

7. Permanent Magnet vs. Electromagnet
Permanent Magnet Electromagnet
Design: hard magnetic material Design: Uses a solenoid to create
magnetic field
Use: for applications where
magnetism is needed over long
periods –fridge doors
Use: For applications where,
magnetic field needs to be
turned on & off -scrap metal
moving