NEET Solved Paper 2018 Question 19
Question: The refractive index of the material of a prism is $ \sqrt{2} $ and the angle of the prism is $ \text{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 [NEET - 2018]
Options:
A) $ \text{30 }{}^\circ $
B) $ 45{}^\circ $
C) $ 60{}^\circ $
D) Zero
Show Answer
Answer:
Correct Answer: B
Solution:
- For retracing its path, light ray should be normally incident on silvered face. Applying Snell’s law at M, $ \frac{\sin i}{\sin 30{}^\circ }=\frac{\sqrt{2}}{1} $
$ \Rightarrow \sin i=\sqrt{2}\times \frac{1}{2} $ $ \sin i=\frac{1}{\sqrt{2}}i.e.i=45{}^\circ $
