A circular coil of current-carrying wire has the normal to its area pointing upward. A second smaller concentric circular coil carries a current in the opposite direction.
(a) Where, in the plane of these coils, could the magnetic field be zero: (1) only inside the smaller one, (2) only between the inner and outer one, (3) only outside the larger one, or (4) inside the smaller one and outside the larger one?
(b) The larger one is a 200-turn coil of wire with a radius of 9.50 cm and carries a current of 11.5 A. The second one is a 100-turn coil with a radius of 2.50 cm. Determine the current in the inner coil so the magnetic field at their common center is zero. Neglect the Earth’s field.