magnet and magnetism in physics

Magnet and Magnetism

Magnet : it is substance that attract magnetic material.                                                  Magnetic material: it any substance that can be attracted by magnet. Examples are iron nickel, steel cobalt and some alloys. Substance such as brass, wood, copper and glass cannot be attracted by magnet, therefore they are called non-magnetic material.

Properties of Magnet

  1. Magnet has north and south poles, where attracting is greatest
  2. A suspended bar magnet must come to rest with it axis point North-south.
  3. Like pole repel each other while the unlike poles attract each other.

How to test for polarity of magnet:

This done by bringing unknown pole near to known pole,  if it repel each other , it shows that the pole is similar to the known one. But if it attracts, no firm conclusion is made, since attraction can also be obtained by a pole of magnet and unmagnetised magnetic material. So repulsion is the only sure test for polarity.

Read also Electric field

Theory of Magnet and  magnetism

When a bar magnet is cut into two, they form two magnets with each having half of the strength of the original magnet. The process can be continued repeatedly dividing a magnet into two and obtain smaller magnet. The smallest magnet we can obtain is one molecule.

Magnetization and de-magnetization

Magnetization: it a process of making a magnetic material a magnet. There are about three ways of magnetization of magnetic material;

  1. Electrical method: This is the best way to make magnet from magnetic material. It is done by inserting magnetic material into solenoid (coil of wire with many turns), then pass a steady direct current through the solenoid, after some time, the material is removed and the magnet is formed. The polarity of this magnet depends on the direction of current.
  2. Single stroke method: Here the material is stroked from one end to the other end several times in the same direction with one pole of a magnet.
  3. Double or divided touch method: Here the material is stroked from the center outwards with unlike pole of two magnet simultaneously. This method is better than single touch method, but electrical method is the best.
  4. Magnetization by induction: The example of this is when nail is brought close to magnet, will be magnetized and if other nail is brought close to the magnetized nail it will be magnetized by it. This shows that the first nail has been made magnet by induction.

Demagnetization: it is process by which magnet is made to lose its magnetism. Molecule must be shaken to demagnetize a magnet. The best way to demagnetize a magnet is to put it into solenoid and allow the alternating current to pass through the solenoid. Another method of destroying magnet is by heating it until is read hot, and then allow it to cool while lying along east-west direction. Note that any rough treatment of magnet of magnet, like dropping and hammering in east-west direction can make it to lose its magnetism.

Comparisons between the magnetic properties of iron and steel

  1. Iron is easily magnetized than steel
  2. Iron is easily de-magnetized than steel.
  3. In solenoid iron become more strongly magnetized than steel
  4. Steel keep it magnetism longer than iron

Exercise Base on magnet and magnetism

  • Define magnetization and de-magnetization
  • How do determine the polarity of a magnet
  • State the theory of magnetism
  • List the magnetic properties of iron and steel
  • What is magnetic induction.

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