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Physics

Magnets and Magnetization

A magnet is a piece of material that can attract iron and other ferromagnetic material.

Generators used in production of electrical power all depends on powerful and efficient magnets  and magnetic materials.

Properties of Bar Magnets

Properties of bar magnets include:

  1. Direction:When a magnet is freely suspended, it comes to rest in the South-North direction of the earth.
  2. Attraction: A magnet has the ability to attract magnetic materials e.g, steel, iron, etc.
  3. Force:A magnet exerts force on other magnets in such a manner that like poles repel and unlike poles attract.
  4. The inseparable nature of poles on the magnetic dipoles: If a magnet is broken into small pieces, however small it may be, it will still have a North and South Poles. The smallest bit of a magnet is adipole.
  5. Magnetic lines of force originate from the North pole and terminate at the South pole.

Methods of Making Magnets

1. Electrical Method:

The best method of making magnets is to use the magnetic effect of an electric current. The material, a steel bar X to be magnetized is placed inside a solenoid; then, the current is switched on for a few seconds and then switched off. When the bar is tested, it is found to be a  magnet.

magnet-electric-method

2. Single Touch:

The material X to be magnetized is placed on a table(bench). The pole of a magnet Yis then dragged alone X from one end to the other and lifted well away. It is brought back  again to X at the far end and the process is repeated several times.

magnetic-singletouch

3. Divided or Double Touch:

The material X is stroked repeatedly in opposite direction by the opposite poles of the two bar magnets A and B. The stroking begins in the middle of X each time.

magnet-double

4. Hammering in the Earth’s Field:

A weak magnet could be made by using the influence of the earth’s magnetic field. This field acts  at an angle to the horizontal called the ‘’angle of Dip’’. It varies from place to place. It is about 70° in England and Britain. If it is done in the N-hemisphere, the lower end will be N and same with S-hemisphere.

earth-magnetic-field

Demagnetisation

This is the process of making a magnet to lose its magnetic properties. It is the removal of the  ferromagnetic properties of a body by disordering the domain structure of that body. Methods of demagnetization include:

  1. Hammering: magnets can be partially demagnetized by hammering them hard when they are  pointing East-West, that is0, at 90° to the earth’s magnetic field direction.
  2. Heating: They can also be partially demagnetized by heating them strongly.
  3. Electrical method: This is the best method of demagnetization. Here, alternating current is used.  The bar magnet to be demagnetized is placed inside the solenoid with its axis pointing east-west.  A rheostat is added to adjust the current’s value. The a.c is switched on and after a few seconds,  the bar is slowly withdrawn from the solenoid to a far distance away.
demagnitisation

Applications of Electromagnets

An electromagnet is made up of a soft iron core around which an insulated wire is wound. It  becomes a magnet only when current flows in the wire. It is a temporary magnet and all temporary  magnets are made of soft iron core.

The strength of electromagnets increases with:

  1. Increase in the current within the coil;
  2. Increase in the number of turns of wire of the coil;
  3. Decrease in distance between the poles of the magnet.

The applications/uses include:

  1. Electromagnets are used in cranes to lift up heavy loads and objects made of magnetic materials like iron.
  2. They are used in making electric devices like electric bell, magnetic relay, switches, telephones earpiece, etc.

Temporary and Permanent Magnets

  1. A temporary magnet is made up of soft iron core while a permanent magnet is made of strong iron.
  2. A temporary magnet only becomes a magnet when current flows through it; but a permanent magnet still maintains its magnetic alignment structure even when there is no flow of current.
S/NTemporary MagnetPermanent Magnet
1Made from soft iron, mu-metalMade from steel, ticomal,
alicomax, cobalt, nickel
2Can be easily magnetizedCannot be easily magnetized
3Can be easily demagnetizedCannot be easily demagnetized

EVALUATION (POST YOUR ANSWERS USING THE QUESTION BOX BELOW FOR EVALUATION AND DISCUSSION):

  1. What is demagnetization?
  2. State the uses of electromagnets.
  3. Mention the various ways of making magnets.

GENERAL EVALUATION (POST YOUR ANSWERS USING THE QUESTION BOX BELOW FOR EVALUATION AND DISCUSSION):

  1. List two applications of electromagnets.
  2. How can the strength of electromagnets be enhanced?
  3. Itemise the various ways of making magnets

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