# A solenoid coil has 50 turns per cm along its length and a cross sectional area of $4cm^2$, 200 turns of another wire are wound round the first solenoid co-axially. The two coils are electrically insulated from each other. Calculate the mutual inductance between the two coils.
(a) $5.024 \times 10^{-3} H$
(b) $5.024 \times 10^{-4} H$
(c) $5.024 \times 10^{-2} H$
(d) $5.024 H$