Magnetization
Magnetization is the process of making magnets from magnetic materials. The following are methods used to make magnets.
1. Magnetizing
by induction
This is a process by which magnets are made by placing ferromagnetic materials in a magnetic field. Materials like iron lose their magnetism
easily and are said to be soft
while others like steel gain magnetism slowly but retain it
longer and are therefore said to be hard and are used to make permanent magnets.
2. Magnetizing by stroking
The object to be magnetized is placed on a bench then a bar
magnet is dragged along the length of the bar from one end to the other. This is repeated several times and the object
becomes magnetized. There are two types of stroking; single-stroke and double-stroke
Procedure:
- The steel bar is stroked
with the same
pole of the permanent magnet from one end to the other end
in one
direction.
- The stroking magnet has
to be
lifted sufficiently high above the steel bar between
successive strokes.
- The steel bar will become a magnet with
pole produced at the end where the strokes finish is opposite
to the stroking pole used as the atomic magnets in the domain are
attracted to the stroking pole.
Note:
- When using two magnets,
the stroking
pole used in each magnet has to be opposite,
and they stroke the steel bar in
opposite direction.
- Using two magnets to
stoke is faster
than that using one magnet.
- Stroking method only
produces weak
magnets.
3. Magnetizing using an electric current
This is the use of magnetic effect of an electric
current through a solenoid (insulated wire of many turns).
When direct current
flows through a solenoid, a magnetic field is created. If a core made
from a magnetic material is placed inside a solenoid, the core will
become magnetised. A relatively small current can create a strong magnet.
A core made from a hard
magnetic material will keep its magnetism after the current has been turned
off.
The magnetic poles can be
determined using the right hand grip rule:
·
Curl the fingers of your right
hand in the direction of the conventional current in the solenoid and
extend your thumb.
·
The thumb points to the
north pole .
The
strength of the electromagnet is affected by:
i.
Amount of current- large
current causes a stronger electromagnet
ii.
Length of the solenoid: a
longer solenoid produces a stronger electromagnet
iii.
Type of the core
iv.
Shape of the core: a u-shaped
core causes a stronger electromagnet than a straight core
Demagnetizing
Demagnetizing is the process of removing magnetic properties of a magnet. The following methods are which a magnet can lose its magnetism;
i.
Hammering them hard with their poles facing E-W direction
ii.
Heating them strongly
iii.
Placing a magnet inside a solenoid and passing an a.c. current through it
for a short
time.
Storing magnets
·
Magnets should be stored in pairs with unlike poles adjacent to each other attached
to pieces of soft iron called keepers.
The
keepers ensures that dipoles are arranged in closed loops hence maintaining
their alignment. This therefore retains magnetism in the magnets.
- Magnets should not be hammered especially with their poles facing E-W direction
- Magnets should not be heated strongly or dropped roughly on hard surfaces.
- Magnets should not be placed near alternating currents.
- Magnets should be kept dry and clean since rust
can make them lose their magnetism.
