The force between two magnetic poles separated by a distance 'd' in air is F. At what distance between them the force becomes doubled.

Explanation

According coulomb.s law we can write,
`F = (mu_0)/(4pi) (m_1 m_2)/(d^(2))`
i.e., ` F prop (1)/(d^(2)) implies (F_1)/(F_2) = (d_2^(2))/(d_1^(2))`
`implies d_2^(2) = (F_1)/(F_2)d_1^(2) = (F)/(2F)d^(2) = (d^(2))/(2) or d_2 = (d)/(sqrt(2))`