A light ray hits the pole of a thin biconvex lens as shown in fig. The angle made by the emergent ray with the optic axis will be approximately

Options

A. `0^(@)`
B. `(1//3)^(@)`
C. `(2//3)^(@)`
D. `2^(@)`

Answer

c.

Explanation

`2mutheta=mu(2^(@))rArr theta=1^(@)`
`alpha=theta-gamma`
`beta(3mu)=(2mu)alpha rArr beta=(2)/(3)(theta-gamma)`
Angle made by emergent ray with optic axis is
`=beta+gamma`
`=(2)/(3)(theta+gamma)+gamma=(2)/(3)theta-(gamma)/(3) cong (2)/(3)xx1^(@)=((2)/(3))^(@)`
[because `gamma cong 0^(@)` for thin lens]