Question

A metal ring 4.00 cm in diameter is placed between the north and south poles of large magnets with the plane of its area perpendicular to the magnetic field. These magnets produce an initial uniform field of 1.12 T between them but are gradually pulled apart, causing this field to remain uniform but decrease steadily at 0.200 T/s.
(a) What is the magnitude of the electric field induced in the ring?
(b) In which direction (clockwise or counterclockwise) does the current flow as viewed by someone on the south pole of the magnet?

Answer 1

Explanation:

a) d[phi]/dt = (dB/dt)*Acos(0) = (-0.20)*(pi(2.25*10^-2)^2) = -3.98*10^-4 Wb

E = (1/2r*pi)*(d[phi]/dt) = -2.8*10^-3 N/C

b) Clockwise because The induced magnetic field will be in the direction to oppose the change. Since the magnetic flux from the magnets is decreasing, the induced magnetic field will be in the same direction as the magnet's field.