Physics Electromagnetic Induction ETEA 2022
PMDC Verified Question 48 of 69
AC generator stops suddenly when:
A
External voltage overcomes the back emf
B
Torque of back emf exceeds the external torque
C
Resistance of the coil produces heat
D
Moment of inertia of the coil decreases
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Torque of back emf exceeds the external torque
Concept:

According to Lenz's Law, generating current creates a magnetic field that opposes the very rotation producing it (a braking effect or "back torque").

Solution:

  • To keep a generator spinning, an external mechanical torque must be constantly applied (like a turbine).


  • If the electrical load draws too much current, the opposing torque of the back EMF (magnetic braking) exceeds the applied external torque, causing the generator to physically stall or stop.


Why other options are incorrect:

Heat from resistance reduces efficiency but doesn't instantly stop rotation. Moment of inertia relates to mass distribution and doesn't spontaneously change. External voltage refers to motors, not the physical stalling of a generator.

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