NEET Solved Paper 2014 Question 38
Question: The angle of a prism is A. One of its refracting surfaces is silvered. Light rays falling at an angle of incidence 2 A on the first surface returns back through the same path after suffering reflection at the silvered surface. The refractive index $ \mu $ , of the prism is [AIPMT 2014]
Options:
A) $ 2\sin A $
B) $ 2\cos A $
C) $ \frac{1}{2}\cos A $
D) $ \tan A $
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Answer:
Correct Answer: B
Solution:
For the given condition above ray diagram will sift.
$ \angle MON=90-\overset{{}^\circ}{\mathop{A}}, $ So $ \angle r=90-(90-A) $
$ \Rightarrow $ $ \angle r=\overset{{}^\circ }{\mathop{A}}, $ By Snell?s law $ \frac{\sin i}{\sin r}=\mu $ $ \frac{\sin (2A)}{\sin (A)}=\mu $ $ \frac{2\sin A\cos A}{\sin A}=\mu $
$ \Rightarrow $ $ \mu =2\cos A $
