Q26 / 116 · NTA Abhyas (JEE Main) 2020 · Physics · Ray Optics

A prism of refractive index 32 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

Solution

The monochromatic ray of light will retrace its path if it strikes the mirror perpendicularly.

Figure

Using Snell's law of refraction,

1×sinθ=μ×sin45°

⇒sinθ=32×sin45°

sinθ=32×12=32

⇒θ=60°

Hence, the correct answer is 60.

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