Magnetization and Dagnetization

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:

1. The steel bar is stroked with the same pole of the permanent magnet from one end to the other end in one direction.
2. The stroking magnet has to be lifted sufficiently high above the steel bar between successive strokes.
3. 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.