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Question #43122
The Question
A plane electromagnetic wave of angular frequency is incident from vacuum onto the flat surface of a uniaxial anisotropic crystal. The boundary is the - plane (), and the crystal occupies the region . The plane of incidence is the - plane, and the angle of incidence is . The optic axis of the crystal lies along the -axis. The ordinary and extraordinary refractive indices of the crystal are and , respectively. If the incident wave is linearly polarized such that it excites only the extraordinary wave in the crystal, what is the angle of refraction of the ray (the direction of energy flow) with respect to the -axis inside the crystal?
Options
- A.
- B.
- C.
- D.
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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
Snell’s Law Vector Form|Boundary Condition Reflection|Vector Analysis
Why This Question Is Tricky
Common Mistakes
This question tests the distinction between the wave vector (phase velocity direction) and the ray vector (group velocity/energy flow direction) in anisotropic media.
Students commonly fall into the trap of applying the scalar Snell's law () using either or , which incorrectly assumes the ray and wave vectors are collinear.
The correct physical framework requires using the vector form of Snell's law to enforce the continuity of the tangential wave vector, and subsequently applying the gradient of the dispersion relation () to determine the true direction of energy propagation.
Quick Facts About This Question
Question Information
| Subject | Physics |
| Chapter | Ray Optics and Optical Instruments - Class 12 |
| Concept | Snell’s Law Vector Form |
| Difficulty | 8 |
| Cognitive Load | 7 |
| Target Solve Time | 160 sec |
| Access | Free |