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Question #43107

Difficulty: 8/10 | 🟢 Free

The Question

A uniform electric field E(t)=E0cos⁡(ω0t)k^\mathbf{E}(t) = E_0 \cos(\omega_0 t) \hat{k} is maintained in a cylindrical region of space of radius RR. The region is filled with a non-magnetic, non-conducting dielectric medium whose permittivity is externally modulated such that it varies with time as ϵ(t)=ϵ0(1+βcos⁡(Ωt))\epsilon(t) = \epsilon_0 (1 + \beta \cos(\Omega t)). Here, E0=100 V m−1E_0 = 100 \text{ V m}^{-1}, ω0=106 rad s−1\omega_0 = 10^6 \text{ rad s}^{-1}, β=0.1\beta = 0.1, and Ω=2×105 rad s−1\Omega = 2 \times 10^5 \text{ rad s}^{-1}. Due to the Ampere-Maxwell law, an induced magnetic field B\mathbf{B} is generated inside the cylinder, containing components oscillating at multiple angular frequencies. What is the ratio of the amplitude of the magnetic field component oscillating at angular frequency ω0+Ω\omega_0 + \Omega to the amplitude of the component oscillating at angular frequency ω0\omega_0?

Options

  • A.

    0.060.06

  • B.

    0.050.05

  • C.

    0.010.01

  • D.

    0.120.12

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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

Spectrum Order and Frequency/Wavelength|Ampere’s Law Displacement Current|Integration

Why This Question Is Tricky

Common Mistakes

This question tests the rigorous definition of Maxwell's displacement current in a non-stationary medium.

Students often misapply the formula by assuming Jd=ϵ∂E∂t\mathbf{J}_d = \epsilon \frac{\partial \mathbf{E}}{\partial t}, forgetting that the fundamental definition is Jd=∂D∂t=∂(ϵE)∂t\mathbf{J}_d = \frac{\partial \mathbf{D}}{\partial t} = \frac{\partial (\epsilon \mathbf{E})}{\partial t}.

In a medium with time-varying permittivity, the product rule dictates Jd=ϵ∂E∂t+E∂ϵ∂t\mathbf{J}_d = \epsilon \frac{\partial \mathbf{E}}{\partial t} + \mathbf{E} \frac{\partial \epsilon}{\partial t}.

Ignoring the second term leads to the incorrect ratio of 0.050.05, failing to account for the full parametric frequency shift caused by the temporal variation of the medium's dielectric properties.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterElectromagnetic Waves - Class 12
ConceptSpectrum Order and Frequency/Wavelength
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree