A large glass slab $\left(\mu=\frac{5}{3}\right)$ of thickness 8 $\mathrm{cm}$ 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 $R \mathrm{~cm}$. What is the value of $R$ ?

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Aicharya · Accepted Answer

$ \frac{R}{t}=	an 	heta_C $ or $\quad R=t\left(	an 	heta_Cight)$ $ \begin{aligned} & 	ext { But, } \quad \sin 	heta_C=\frac{1}{\mu}=\frac{3}{5} \ & 	herefore \quad 	an 	heta_C=\frac{3}{4} \ & 	herefore \quad R=\frac{3}{4} t=\frac{3}{4}(8 \mathrm{~cm})=6 \mathrm{~cm} \ & \end{aligned} $ Hence the answer is 6 .

A large glass slab $\left(\mu=\frac{5}{3}\right)$ of thickness 8 $\mathrm{cm}$ is placed over a point source…

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