Optics 7 Question 34
35. 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)
Analytical & Descriptive Questions
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Solution:
- $\frac{R}{t}=\tan \theta _C \quad$ or $\quad R=t\left(\tan \theta _C\right)$
$$ \begin{array}{ll} \text { But, } & \sin \theta _C=\frac{1}{\mu}=\frac{3}{5} \\ \therefore & \tan \theta _C=\frac{3}{4} \\ \therefore \quad R=\frac{3}{4} t=\frac{3}{4}(8 cm)=6 cm \end{array} $$
Hence the answer is 6 .
