Optics 1 Question 7
7. Two plane mirrors $A$ and $B$ are aligned parallel to each other, as shown in the figure. A light ray is incident at an angle $30^{\circ}$ at a point just inside one end of $A$. The plane of incidence coincides with the plane of the figure. The maximum number of times the ray undergoes reflections (including the first one) before it emerges out is
(2002, 2M)
(a) 28
(b) 30
(c) 32
(d) 34
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Answer:
Correct Answer: 7. (b)
Solution:
- $d=0.2 \tan 30^{\circ}=\frac{0.2}{\sqrt{3}}$
$$ \frac{l}{d}=\frac{2 \sqrt{3}}{0.2 / \sqrt{3}}=30 $$
Therefore, maximum number of reflections are 30 .
NOTE Answer of this question may be 30 or 31 .
