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Question #43742

Difficulty: 8/10 | 🟢 Free

The Question

A p-polarized plane electromagnetic wave is incident from vacuum (n1=1n_1 = 1) onto a non-magnetic dielectric medium with refractive index n2=3n_2 = \sqrt{3}. The interface at z=0z=0 is coated with an ultra-thin metamaterial that acts as a localized displacement current source, providing an effective surface current density K⃗=σsE⃗t\vec{K} = \sigma_s \vec{E}_t, where E⃗t\vec{E}_t is the tangential electric field and σs\sigma_s is a real constant. The incident magnetic field is given by H⃗i=H0cos⁡(kxx+kzz−ωt)y^\vec{H}_i = H_0 \cos(k_x x + k_z z - \omega t) \hat{y}. It is observed that the reflected wave is completely extinguished when the angle of incidence is θi=arcsin⁡(12/13)\theta_i = \arcsin(12/13). Given the impedance of free space is Z0=μ0/ϵ0Z_0 = \sqrt{\mu_0/\epsilon_0}, what is the value of the dimensionless parameter σsZ0\sigma_s Z_0?

Options

  • A.

    13(11−53)55\frac{13(11 - 5\sqrt{3})}{55}

  • B.

    13(53−11)55\frac{13(5\sqrt{3} - 11)}{55}

  • C.

    0

  • D.

    13(11+53)55\frac{13(11 + 5\sqrt{3})}{55}

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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

Brewster's Law|Wave Equation Sign Convention|Displacement Current Source

Why This Question Is Tricky

Common Mistakes

This question tests the fundamental origin of Brewster's angle by disrupting the standard boundary conditions.

Students typically memorize tan⁡(θB)=n2/n1\tan(\theta_B) = n_2/n_1, which assumes continuity of the tangential magnetic field (Option C trap).

By introducing a localized displacement current (effective surface current) at the boundary, the Ampere-Maxwell law (∇×H⃗=J⃗f+∂D⃗/∂t\nabla \times \vec{H} = \vec{J}_f + \partial \vec{D}/\partial t) dictates a jump in the tangential H-field.

Students must re-derive the Fresnel reflection coefficient from first principles, correctly applying the wave equation sign convention to relate E and H fields, and solve the modified boundary value problem to find the new zero-reflection condition.

A sign error in the boundary condition cross product leads to Option B.

Quick Facts About This Question

Question Information

SubjectPhysics
ChapterWave Optics - Class 12
ConceptBrewster's Law
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree