Topic: Refraction through a prism· Optics

The refractive index of the material of a prism is 2 and the angle of the prism is 30^°. One of the two refracting surfaces of the prism is made a mirror inwards, by silver coating. A beam of monochromatic light entering the prism from the other face…

The refractive index of the material of a prism is \(\sqrt2\) and the angle of the prism is \(30^\circ\). One of the two refracting surfaces of the prism is made a mirror inwards, by silver coating. A beam of monochromatic light entering the prism from the other face will retrace its path (after reflection from the silvered surface) if its angle of incidence on the prism is

1. \(60^\circ\)

2. \(30^\circ\)

3. \(45^\circ\)

4. zero

Doubtly Asked 30 Oct 2026 NEET UG 2018 Practice test neet Save WhatsApp Report

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Answer: 3. \(45^\circ\)

The ray retraces its path only if it strikes the silvered face normally.

The prism angle is \(A=30^\circ\). For a ray hitting the second face normally, \(r_2=0\), so \(r_1=A-r_2=30^\circ\).

Snell's law at the first face: \(\sin i=\mu\sin r_1=\sqrt2\times\tfrac12=\dfrac1{\sqrt2}\), so \(i=45^\circ\).

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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The refractive index of the material of a prism is 2 and the angle of the prism is 30^°. One of the two refracting surfaces of the prism is made a mirror inwards, by silver coating. A beam of monochromatic light entering the prism from the other face…

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