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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

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

$F = mB= \large\frac{\mu_0}{4 \pi}$ $\large\frac{2m'l}{x^3}$$m$
Ans : (a)