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Question #42974
The Question
A small square conducting loop of mass (in kg), side length (in m), and electrical resistance (in ) is attached to the lower end of a massless rigid rod of length (in m). The upper end of the rod is pivoted so the loop can oscillate as a pendulum in the vertical -plane ( is horizontal, is vertical). A time-independent magnetic field (in T) exists in the region, where and are positive constants. An external horizontal driving force (in N) is applied to the loop. Assuming small amplitude oscillations, negligible self-inductance, and no air drag, what is the average electrical power (in W) dissipated in the loop when the system is driven at its velocity resonance frequency?
Options
- A.
- B.
- C.
- D.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Intuition_Breaker
Train your brain to resist "obvious" answers that are designed to deceive your intuition.
Concepts Behind This Question
Lenz’s Law Energy Conservation|Driven Oscillations and Resonance|Faraday’s Law Vector Form
Why This Question Is Tricky
Common Mistakes
This question traps students who blindly apply the motional EMF formula using the background field , incorrectly yielding a damping coefficient .
It tests the critical understanding that in a uniform field, a translating loop experiences no net flux change; the damping arises purely from the magnetic field gradient .
Furthermore, it probes the mechanics of driven damped oscillators: students often misapply energy conservation by treating the system as a conservative Simple Harmonic Oscillator, failing to recognize that at velocity resonance, the external driving power is entirely dissipated by the non-conservative eddy current damping.
Quick Facts About This Question
Question Information
| Subject | Physics |
| Chapter | Electromagnetic Induction - Class 12 |
| Concept | Lenz’s Law Energy Conservation |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |