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Question #43391
The Question
A long non-conducting solid cylinder of radius has a time-varying volume charge density given by , where is a positive constant, is the radial distance from the central axis, and is time. The cylinder rotates about its central longitudinal axis with a constant angular velocity . A closed conducting loop is formed in a plane perpendicular to the cylinder's axis (far from the ends). The loop consists of a stationary radial wire from the axis to , a stationary circular arc of radius , and a conducting rod of length pivoted at the axis. The rod rotates with a constant angular velocity in the same sense as , continuously expanding the sector area of the loop. At , the rod coincides with the stationary radial wire. Find the magnitude of the total induced electromotive force (EMF) in the loop at time . Assume all quantities are in SI units and ignore self-inductance.
Options
- A.
- B.
- C.
- D.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Multi-Concept_Bridge
Master problems that require linking physics and math concepts to solve complex competitive questions.
Concepts Behind This Question
Biot-Savart Law Vector Symmetry|Motional EMF in Rotating Rods|Vector Decomposition Ambiguity
Why This Question Is Tricky
Common Mistakes
This question tests the synthesis of Ampere's law for continuous rotating charge distributions with Faraday's law in a non-steady state.
The primary trap is the 'Time-varying Fields' misconception: students often mechanically apply the motional EMF formula and forget that when the magnetic field itself is explicitly time-dependent, a transformer EMF is also induced.
Calculating only the motional EMF leads to Option B.
Furthermore, assuming a uniform magnetic field based on the center value bypasses the necessary spatial integration of the non-uniform field, leading to Option C.
Quick Facts About This Question
Question Information
| Subject | Physics |
| Chapter | Moving Charges and Magnetism - Class 12 |
| Concept | Biot-Savart Law Vector Symmetry |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |