A large glass slabe `(mu=5//3)` of thickness 8cm is placed over a point source of light on a plane surface. It is seen that light emerges out of th etop surface fo the slab from a circular area of radius R cm. What is the value of R?

Options

A. 6 cm
B. 7 cm
C. 8 cm
D. 9 cm

Answer

A

Explanation

From the figure, we have
`(R)/(t)=tantheta_(C)`

or `R=t(tantheta_(C))`
But, `sintheta_(C)=(1)/(mu)=(3)/(5)`
`thereforetantheta_(C)=(3)/(4)`
`R=(3)/(4)t=(3)/(4)(8cm)=5cm`
Hence, the answer is 6.