Which of the following is the CORRECT effect for the back electromotive force (e.m.f.) in thecurrent of an alternating current (A.C.) motor?
Correct answer: D. It decreases the current in the motor.
- A. It does not have any effect.
- B. It reverses the direction of current.
- C. It increases the current in the motor.
- D. It decreases the current in the motor.
Explanation
Because the back e.m.f. acts in opposition to the supply voltage, the net voltage across the motor's windings is the difference between the applied voltage and the back e.m.f. As the motor speeds up, the magnitude of the back e.m.f. increases. This increased opposing voltage reduces the net voltage available to drive the current through the motor's coils. According to Ohm's Law (Current = Voltage / Resistance), a reduced net voltage leads to a decreased current flowing through the motor.
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About Faraday's Law
Faraday's law states that an induced electromotive force equals the rate of change of magnetic flux linkage through a circuit. Questions cover changing field, area, angle or motion, the negative sign associated with Lenz's law, and the distinction between induced emf and the current that may flow in a closed circuit.
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