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?

Answer

6

Explanation

`tanC=(R)/(8) ……..(i)`
`(5)/(3) sinC=1.sin90^(@)`
`sinC=(3)/(5)`
`C=37^(@)`
`(3)/(4)=(R)/(8)`
`R=6 cm` .