Two magnetic poles, one of the which is four times stronger than the other, exert a force of 10gf on each other when placed at a distance of 20cm. Find the strength of each pole.

Explanation

Let the pole strength of the two dipoles be m and 4 m
and `" " r = 20` cm = `0.2` m
Using Coulomb's law of magnetism , `F = (mu_(0))/(4pi) . (m_(1)m_(2))/(r^(2))`
Substituting the values , `10 xx 10^(-3) xx 9.8 = -(10^(-7) xx m xx 4m)/((0.2)^(2))`
or `" " m^(2) = (10 xx 9.8 xx (0.2)^(2) xx 10^(4))/(4) = 9800`
or `" " m_(1) = m = 98.9 Am`
`m_(2) = 4 m = 4 xx 98.9 = 396 ` Am