# The force experienced by a pole of strength $100\: A-m$ at a distance of $0.2 \: m$ from a short magnet of length $10\: cm$ and pole strength $100\: A-m$ on its axial line will be

$\begin {array} {1 1} (a)\;2.5 \times 10^{-2}N & \quad (b)\;5.0 \times 10^{-2}N \\ (c)\;2.5 \times 10^{-3}N & \quad (d)\;5.0 \times 10^{-3}N \end {array}$

F = mB
\begin{align*}= \frac{\mu_0}{4 \pi} \times \frac{2 m' l}{x^3} \times m \end{align*}
\begin{align*}= \frac{10^{-7} \times 2 \times 100 \times 0.1 \times 100}{8 \times 10^{-3}} \end{align*}
$= 2.5 \times 10^{-2} N$
answered Feb 22, 2014
edited Nov 24, 2017