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A prism of refractive index 3 2 and refracting angle is 45 ° is placed in air. One of the two refracting surfaces of the prism is silvered and a ray of monochromatic light enters the prism from the other face at an angle θ . If the ray retraces its path, then what is the value of θ (in degree)?

Correct answer

60

Step-by-step solution

The monochromatic ray of light will retrace its path if it strikes the mirror perpendicularly. Using Snell's law of refraction, 1 × sin θ = μ × sin 45 ° ⇒ sin θ = 3 2 × sin 45 ° sin θ = 3 2 × 1 2 = 3 2 ⇒ θ = 60 °

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