Magnetism-Introduction

MAGNETISM

Contents

•  Magnets and non-magnetic materials
  • Properties of magnets
  • Law of magnetism
  • Magnetic field
  •  Magneticshielding
  • Magnetization(Making magnets)
  • Demagnetizing
  • Storing magnets
  • Domain theory of magnetism.
  • Hard and soft magnetic materials
  • Facts about magnets

 

Introduction

Magnets are substances that are able to attract and hold certain types of materials, known as magnetic material. Lodestone is the only known natural magnet which was discovered by the Chinese 2,000 years ago. Other magnets produced artificially by man are artificial magnets.

Uses of magnets

1.   Used in making other magnets

2.   Used in making loud speakers

3.   Used in making moving coil meters

4.   Used in making telephone speakers.

Magnets and non-magnetic materials

Magnetic materials are those that are attracted by magnets. Examples include iron, steel, cobalt and nickel.

Non-magnetic ones are those that are not affected by magnets. Wood, glass and copper are examples of non-magnetic substances.

Diamagnetic materials are those that are repelled by magnets.

Ferromagnetic materials are those which are strongly attracted by magnets. Examples ar iron, nickel, cobalt.

Paramagnetic materials are the materials that are so lightly attracted such that the magnet seems to have no effect on them are called (mostly non-magnetic materials).

Ferrites are a mixture of iron oxide and barium oxide are the most newly developed magnetic materials. Ceramic magnets or magnadur magnets are made from ferrites and are very strong.

Properties of magnets

1.     Magnetic poles: magnets are double poled substances with both the North and South poles. When a bar magnet is broken into small pieces, every piece acquires North and South pole

The strength of a magnet is at the poles. This can be shown by dipping into or sprinkling iron fillings on the magnet.

The greatest magnetic force is concentrated around the poles of a magnet.

QUIZ: Describe an experiment to show that the strength of a magnet is at the poles

2.     Directional property: when a magnet is suspended freely with a string, it always settles in a north-south direction. The side facing north is the North Pole while South Pole is the side facing pointing to the south.

 

This is the method used to identify the poles of a magnet as well identifying magnets.

QUIZ: Given two rods, one a bar magnet and the other an iron rod. Using a string, describe how you would identify the bar magnet.

Law of magnetism

Like poles repel and unlike poles attract.

If two bar magnets are pushed together end to end, then they will either attract each other or repel each other depending on which polarities are used. Like Poles repel – Two North poles will repel each other (push each other away). Two South poles will also repel each other. Opposite Poles attract – A North Pole will attract a South Pole (jump towards and stick to each other) Repulsion is a sure method of determining whether two substances are magnets.