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Question #43312
The Question
A stationary circular conducting loop of radius , mass , and specific heat capacity is placed in a uniform magnetic field directed perpendicular to the plane of the loop. The magnetic field varies with time as , where is a positive constant. The initial resistance of the loop at is . The resistance varies with temperature as , where is the initial temperature and is the temperature coefficient of resistance. Assuming no heat is lost to the surroundings, negligible thermal expansion of the loop's dimensions, and negligible self-inductance, what is the time required for the resistance of the loop to become ?
Options
- A.
- B.
- C.
- D.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Variable_Constraint
Develop pure symbolic logic skills by mastering algebraic constraints without relying on numerical data.
Concepts Behind This Question
AC Generator Back-EMF|Relaxation Time Dependency|Resistivity vs Resistance
Why This Question Is Tricky
Common Mistakes
This question tests the student's ability to recognize and model the non-linear coupling between Joule heating and temperature-dependent resistance.
A standard trap is to treat the resistance as a constant throughout the heating process, which leads to the incorrect answer B.
Another trap is to incorrectly average the power dissipation over the interval (leading to answer C).
Because the power is inversely proportional to the instantaneous resistance, the rate of temperature increase slows down as the loop heats up.
Students must set up a differential equation relating to rather than using macroscopic algebraic energy balances, properly integrating the non-ohmic transient behavior.
Quick Facts About This Question
Question Information
| Subject | Physics |
| Chapter | Electromagnetic Induction - Class 12 |
| Concept | AC Generator Back-EMF |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |