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Question #95564

Difficulty: 5/10 | 🟢 Free

The Question

A long cylindrical paramagnetic core is placed in an environment at absolute zero temperature (T0=0 KT_0 = 0\text{ K}). The core is subjected to a superposed external magnetic field intensity H(t)=H0+H0sin⁡(ωt)H(t) = H_0 + H_0 \sin(\omega t), where H0H_0 is a positive constant in A m−1\text{A m}^{-1}. Assume the material is highly paramagnetic such that its susceptibility obeys Curie's Law χ=C/T≫1\chi = C/T \gg 1 (where CC is the Curie constant in K\text{K}), allowing the approximation for the magnetic field inside the core to be B(t)≈μ0χH(t)B(t) \approx \mu_0 \chi H(t). The time-varying component of the magnetic field induces eddy currents, resulting in a time-averaged power dissipation per unit volume given by Pin=αBac,rms2P_{in} = \alpha B_{ac, rms}^2, where Bac,rmsB_{ac, rms} is the root-mean-square value of the AC component of the magnetic field inside the core, and α\alpha is a constant in W m−3T−2\text{W m}^{-3} \text{T}^{-2}. The core dissipates heat to its surroundings at a rate per unit volume given by Pout=βTP_{out} = \beta T, where β\beta is a constant in W m−3K−1\text{W m}^{-3} \text{K}^{-1} and TT is the steady-state absolute temperature of the core. Assuming uniform temperature distribution, what is the total root-mean-square magnetic field Btotal,rmsB_{total, rms} inside the core in the steady state?

Options

  • A.

    (272)1/6(μ0CH0βα)1/3\left( \frac{27}{2} \right)^{1/6} \left( \frac{\mu_0 C H_0 \beta}{\alpha} \right)^{1/3}

  • B.

    (32)1/6(μ0CH0βα)1/3\left( \frac{3}{2} \right)^{1/6} \left( \frac{\mu_0 C H_0 \beta}{\alpha} \right)^{1/3}

  • C.

    (12)1/6(μ0CH0βα)1/3\left( \frac{1}{2} \right)^{1/6} \left( \frac{\mu_0 C H_0 \beta}{\alpha} \right)^{1/3}

  • D.

    (278)1/6(μ0CH0βα)1/3\left( \frac{27}{8} \right)^{1/6} \left( \frac{\mu_0 C H_0 \beta}{\alpha} \right)^{1/3}

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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

Superposition of Magnetic Fields|Curie’s Law|Dynamic Resistance (AC Resistance)

Why This Question Is Tricky

Examiner Levers

Dimensional Analysis

Tests if the student verifies units/dimensions before selecting.

Difficulty Boost : +2

Common Mistakes

This problem tests the coupling of the Superposition Principle with non-linear, temperature-dependent material properties via Curie's Law.

The primary trap lies in misidentifying which component of the superposed magnetic field contributes to eddy current heating; students often erroneously use the total RMS field, ignoring that static (DC) fields do not induce Faraday EMFs.

A secondary trap is failing to correctly superpose the orthogonal DC and AC components when calculating the final total RMS field (Brms=Bdc2+Bac,rms2B_{rms} = \sqrt{B_{dc}^2 + B_{ac, rms}^2}).

By forcing an iterative dependency analysis—where BB depends on TT, TT depends on PinP_{in}, and PinP_{in} depends strictly on the AC component of BB—the question rigorously evaluates the student's ability to isolate physical phenomena within superposed states.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterMagnetism and Matter - Class 12
ConceptSuperposition of Magnetic Fields
Difficulty5
Cognitive Load6
Target Solve Time140 sec
AccessFree