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Question #42760
The Question
A homogeneous cylindrical poorly conducting rod of length (in ), cross-sectional area (in ), and constant permittivity (in ) has an initial uniform electrical conductivity (in ). Due to uniform Joule heating from a prior transient current, the momentum relaxation time of the charge carriers decreases, resulting in a new uniform steady-state conductivity . Immediately after this heating phase, an AC source is connected across the rod, driving a total uniform current (in ) through it, where is the current amplitude and is time. If the angular frequency of the AC source is (in ), which of the following expressions gives the amplitude of the potential difference (in ) across the rod?
Options
- A.
- B.
- C.
- D.
Check Your Answer
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
Conductor Interior Potential|Ohm's Law Validity|Relaxation Time Dependency|Integration
Why This Question Is Tricky
Common Mistakes
This question tests the student's ability to model a conductor under high-frequency AC conditions where the quasi-static assumption () fails.
Students commonly fall into two traps: (1) ignoring the displacement current () which arises from the transient continuity equation, and (2) neglecting the temperature dependence of the momentum relaxation time, which alters the macroscopic conductivity due to Joule heating.
By assuming a purely resistive DC-like behavior (), a student will incorrectly choose option B.
If they account for the displacement current but fail to update the conductivity from its initial state, they will choose option C.
The correct approach requires synthesizing the modified conductivity with the complex admittance of the leaky dielectric.
Quick Facts About This Question
Question Information
| Subject | Physics |
| Chapter | Electrostatic Potential and Capacitance - Class 12 |
| Concept | Conductor Interior Potential |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |