A rectangular loop of sides \(a\) and \(b\) carrying current \(I\) is placed in a magnetic field \(\vec B\) such that its area vector \(\vec A\) makes an angle \(\theta\) with \(\vec B\). With the help of a suitable diagram, show that the torque \(\vec \tau\) acting on the loop is given by
\[
\vec \tau=\vec m\times \vec B,
\]
where
\[
\vec m=I\vec A
\]
is the magnetic dipole moment of the loop.