• # question_answer 9) A bar magnet of length 10 cm and having pole strength equal to ${{10}^{-3}}$ A x m is kept in a magnetic field of $4\pi \,\,\times \,\,{{10}^{-}}^{3}$ Tesla. It makes an angle $30{}^\circ$ with the direction of the field. The torque acting on the magnet is $\left( newton\text{ }\times \text{ }metre \right)$- A) $2\pi \,\,\times \,\,{{10}^{-}}^{7}$                 B) $2\pi \,\,\times \,\,{{10}^{-}}^{5}$C) $0.5$                           D) $\,50$

$M=mL$ $={{10}^{-}}^{3}\,\,\times \,\,0.1$ $={{10}^{-4}}$ $Torque\,\tau \,\,=\,\,MB\text{ }\sin 30{}^\circ$ $={{10}^{-4}}\times 4\pi \times {{10}^{-3}}\times \frac{1}{2}$ $=\,\,\,2\pi \times {{10}^{-}}^{7}\,N-m$