An infinitely long solenoid of radius r0 centred at origin which produces a time-dependent magnetic field \(\frac{α}{\pi r_0^2} \cos ω t\) (where α and ω are constants) is placed along the z-axis. A circular loop of radius R, which carries unit line charge density is placed, initially at rest, on the xy-plane with its centre on the z-axis. If R > r0, the magnitude of the angular momentum of the loop is
1
\(\alpha R(1-\cos \omega t)\)
2
\(\alpha R \sin \omega t\)
3
\(\frac{1}{2} \alpha R(1-\cos 2 \omega t)\)
4
\(\frac{1}{2} \alpha R \sin 2 \omega t\)