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Question #43266
The Question
A spherical ferromagnetic rotor of volume and moment of inertia is free to rotate about a fixed vertical axis. A uniform horizontal magnetic field of magnitude is applied and forced to rotate about the same vertical axis at a constant angular velocity . Due to magnetic hysteresis, the rotor's magnetization vector maintains a constant magnitude but lags behind the rotating magnetic field by a constant angle . The rotor experiences a viscous drag torque , where and is the rotor's angular velocity. Once the rotor reaches its steady-state terminal angular velocity , what is and the rate of internal heat generation within the rotor strictly due to magnetic hysteresis?
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
Torque and Potential Energy in B-Field|Energy Partitioning|Elastic Hysteresis Loop
Why This Question Is Tricky
Common Mistakes
This question tests the student's ability to partition energy in a non-conservative magnetic system, specifically modeling the physics of a hysteresis motor.
Students commonly fall into the trap of assuming the magnetic potential energy is a simple state function () and incorrectly apply conservation of mechanical energy.
They may calculate the total power input and assume it all goes into viscous dissipation (Option B), or they might confuse the mechanical power with the hysteresis loss (Option C).
The core physical insight required is that the magnetic field does work on the material at a rate proportional to the field's rotation , but only a fraction () becomes mechanical work; the 'slip' relative rotation () drives the hysteretic cycle, dissipating energy as internal thermodynamic heat.
Quick Facts About This Question
Question Information
| Subject | Physics |
| Chapter | Magnetism and Matter - Class 12 |
| Concept | Torque and Potential Energy in B-Field |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |