Some Basics of Magnetism

1. Earth behaves as a magnet: This is as if a big magnet is held at the center of the earth with its north pole pointing towards geographic South Pole and South Pole pointing geographical North as shown in the figure.

2. Every magnet attracts small pieces of iron, cobalt, nickel and steel towards it .The attraction is maximum at the two ends of a magnets.

3. When a magnet is suspended freely with the help of thread, it comes to rest along the north south direction. The pole of magnet which points towards geographic north is called North Pole and opposite end facing towards geographic south is call South Pole.

4. Poles exist in pairs; two poles of magnet are always of equal strength. The magnetic length of magnet is 6/7 of actual length of the magnet.

5. A straight line XX’ passing through the south and North Pole is called as axial line. And a line YY’ passing through the centre and perpendicular to length is called equatorial line.

6. A plane passing through N-S line of a freely suspended magnet is called magnetic meridian.

  

7. Like poles repel each other and unlike pole attract each other.

8. The force of attraction and repulsion F between two magnetic poles of strength m1 and m2 separated by a distance r is directly proportional to the product of poles strength and inversely proportional to the square of the distance between the centres.

Magnetic poles said to be one ampere-meter, if it repel s and equal and similar pole with a force of 10^-7 N, when placed in vacuum at a distance of one meter.

9. The magnetic poles exist in pairs and do not exist in monopole. Each piece of a broken magnet is a complete magnet in itself. Isolated magnetic north and south poles are called monopoles and they do not exist.

  

10. When a piece of magnetic material is places near to a magnet, it acquires magnetism. The magnetism so acquired is called induce magnetism and the property of magnet is called inductive property.

11. Repulsion is sure test of magnetism. Two bar magnets repeals each other’s similar poles but they attract the iron piece with both the poles.