A metal ring 4.40 cm in diameter is placed between the north and south poles of

Question

A metal ring 4.40 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 . What is the magnitude of the electrical field induced in the ring? In which direction (clockwise or counterclockwise) does the current flow as viewed by someone on the south pole of the magnet?

Explanation / Answer

change in magnetic flux(phi) through an area A is

closed integral of E.dl = - d(phi)/dt

dL = length of the Circle = 2pir

r = D/2 = 4.4cm/2 = 2.2 cm

phi = B.A

B is magnetic field

A is area = pi r^2

so

E* (2pir) = B* pi r^2

E = - (r/2) dB/dt

E = - 0.022/2 * -(0.2)    ( decreasing)

so

the magnitude of induced electric field E = 2.2 *10^-3 V/m , this is ANTI Clock wise direction

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