The coils of a motor\'s rotor have resistance of 2.0 . When the motor runs at fu

Question

The coils of a motor's rotor have resistance of 2.0 . When the motor runs at full speed, powered by 115V linevoltage it draws a current of 9A.
What is the back electromagnetic field (emf) in this motorunder those conditions? If the motor is prevented from turning, what would be thecurrent drawn? How much more heat would be generated in the coils in thatsituation?
What is the back electromagnetic field (emf) in this motorunder those conditions? If the motor is prevented from turning, what would be thecurrent drawn? How much more heat would be generated in the coils in thatsituation?

Explanation / Answer

a, The net voltage different is 2 x 9 =18V Since the back emf reduce the origin voltage different, 118V -emf = 18 V So back emf =100 V b, If the motor's prevented from turning, the back emf iszero, so the voltage different is 118V Then the current should be 118 / 2 = 59 A. c, If the motor turn: the power is P = U I = 18 x 9 = 162W If not: the power is P' = 118 x 59 = 6962 W So the heat will be generated 6962/162 = 43 times more if themotor doesn't turn

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