Q 12-05-061JEE MainJEE Main 2021 (26 Aug, Shift 1)Medium
Two short magnetic dipoles $m_1$ and $m_2$ each having magnetic moment of $1$ A m$^2$ are placed at point $O$ and $P$ respectively. The distance between $OP$ is $1$ m. The torque experienced by the magnetic dipole $m_2$ due to the presence of $m_1$ is ______ $\times10^{-7}$ N m
Numerical value type. Enter your answer.
Answer: 1
$P$ lies on the equatorial line of $m_1$, where the field is antiparallel to $m_1$:
$$B = \frac{\mu_0}{4\pi}\frac{m_1}{r^3} = 10^{-7}\times\frac{1}{1^3} = 10^{-7}\ \text{T}$$
$m_2$ is perpendicular to $m_1$, hence perpendicular to $B$:
$$\tau = m_2B\sin90^\circ = 1\times10^{-7}\ \text{N m}$$
Solution by Sreeraj P, M.Sc Physics