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# Coulomb’s Inverse Square Law of Magnetism: Solved Example Problems

12th Physics : Magnetism and Magnetic Effects of Electric Current: Coulomb’s Inverse Square Law of Magnetism: Solved Example Problems with Answers, Solution and Explanation

## Coulomb’s Inverse Square Law of Magnetism: Solved Example Problems

EXAMPLE 3.5

The repulsive force between two magnetic poles in air is 9 x 10-3 N. If the two poles are equal in strength and are separated by a distance of 10 cm, calculate the pole strength of each pole.

Solution:

The force between two poles are given by The magnitude of the force is Given :  F = 9 x 10-3N, r = 10 cm = 10 x 10-2 m

Therefore, EXAMPLE 3.6

A short bar magnet has a magnetic moment of 0.5 J T-1. Calculate magnitude and direction of the magnetic field produced by the bar magnet which is kept at a distance of 0.1 m from the center of the bar magnet along (a) axial line of the bar magnet and (b) normal bisector of the bar magnet.

Solution

Given magnetic moment 0.5 J T-1 and distance r = 0.1 m

(a) When the point lies on the axial line of the bar magnet, the magnetic field for short magnet is given by Hence, the magnitude of the magnetic field along axial is Baxial = 1 x 10-4 T and direction is towards South to North.

(b) When the point lies on the normal bisector (equatorial) line of the bar magnet, the magnetic field for short magnet is given by Hence, the magnitude of the magnetic field along axial is Bequatorial = 0.5 x 10-4 T and direction is towards North to South.

Note that magnitude of Baxial is twice that of magnitude of Bequatorial and the direction of Baxial and Bequatorial are opposite.

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