Moving Charges And Magnetism

A solenoid of length \(0.4 \mathrm{~m}\) and having 500 turns of wire carries a current \(3 \mathrm{~A}\). A thin coil having 10 turns of wire and radius \(0.1 \mathrm{~m}\) carries current \(0.4 \mathrm{~A}\). the torque required to hold the coil in the middle of the solenoid with its axis perpendicular to the axis of the solenoid is \(\left(\mu_0=4 \pi \times 10^{-7}\right.\) SI units, \(\left.\pi^2=10\right)\left(\sin 90^{\circ}=1\right)\)