Question
A magnet of magnetic moment $$50\hat i\,A - {m^2}$$ is placed along the $$x$$-axis in a magnetic field $$\vec B = \left( {0.5\hat i + 3.0\hat j} \right)T.$$ The torque acting on the magnet is
A.
$$175\,\hat k\,N{\text{ - }}m$$
B.
$$150\,\hat k\,N{\text{ - }}m$$
C.
$$75\,\hat k\,N{\text{ - }}m$$
D.
$$25\sqrt {37} \,\hat k\,N{\text{ - }}m$$
Answer :
$$150\,\hat k\,N{\text{ - }}m$$
Solution :
$$\vec \tau = \vec M \times \vec B = 50\,\hat i \times \left( {0.5\hat i + 3\hat j} \right) = 150\,\hat k\,N{\text{ - }}m$$