Question

The dipole moment of a short bar magnet is $1.25\, A m ^{2}$. The magnetic field on its axis at a distance of $0.5$ metre from the centre of the magnet is

• A. $1.0 \times 10^{-4} N / Am$
• B. $4 \times 10^{-2} N / Am$
• C. $2 \times 10^{-6} N / Am$
• D. $6.64 \times 10^{-8} N / Am$

Answer 1

Answer: (C)

$B=\frac{\mu_{0}}{4 \pi} \frac{2 M}{d^{3}}=10^{-7} \times \frac{2 \times 1.25}{(0.5)^{3}}$
$=2 \times 10^{-6} N / A - m$