A large 50-turn circular loop of radius 10cm carries a current 4A. At the center of the loop is a small 20-turn coil of radius 0.5cm carrying current 1A. The places of the 2 coils are perpendicular. Find the torque exerted by the large coil on the small coil. ( Neglect any variation in b due to the large coil over the region occupied by the small coil.)