The rotor in a certain electric motor is a flat, rectangular coil with 120 turns

Question

The rotor in a certain electric motor is a flat, rectangular coil with 120 turns of wire and dimensions 3.50 cm by 5.00 cm. The rotor rotates in a uniform magnetic field of 0.600 T. When the plane of the rotor is perpendicular to the direction of the magnetic field, the rotor carries a current of 15.0 mA. In this orientation, the magnetic moment of the rotor is directed opposite the magnetic field. The rotor then turns through one-half revolution. This process is repeated to cause the rotor to turn steadily at an angular speed of 3.60 x 103 rev/min.

(a) Find the maximum torque acting on the rotor.

(b) Determine the amount of work performed by the magnetic field on the rotor in every full revolution.

Explanation / Answer

Here,

Number of turns , N = 120

magnetic field , B = 0.6 T

current ,I = 15 mA = 0.015 A

angular speed , w = 3.6 *10^3 rev/min = 376.92 rad/s

a)

for the maximum torque acting on the motor = N * B * w * I * Area

the maximum torque acting on the motor = 120 * 0.6 * 0.015 * 376.92 * 0.035 * 0.05

the maximum torque acting on the motor = 0.712 N.m

the maximum torque acting on the motor is 0.712 N.m

b)

for a full rotation ,

as the potential energy is same at the initial position and the final position

amount of work performed by magnetic field = U - U

amount of work performed by magnetic field = 0 J

the amount of work performed by magnetic field is 0 J

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