Optics Ques 209
- A large glass slab $(\mu=\frac{5}{3})$ of thickness $8$ $ cm$ is placed over a point source of light on a plane surface. It is seen that light emerges out of the top surface of the slab from a circular area of radius $R$ $ cm$. What is the value of $R$ ?
(2010)
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Answer:
Correct Answer: 209.$(6)$
Solution:
Formula:
Critical Angle and Total Internal Reflection (T. I. R.)
- $\frac{R}{t}=\tan \theta _C \quad$ or $\quad R=t\left(\tan \theta _C\right)$
$\text { But, } \sin \theta _C=\frac{1}{\mu}=\frac{3}{5} $
$\therefore \quad \tan \theta _C=\frac{3}{4} $
$\therefore \quad R=\frac{3}{4} t=\frac{3}{4}(8 cm)=6 cm$
Hence the answer is $6$ .
BETA
