What is the refractive index of material of a plano-convex lens , if the radius of curvature of the convex surface is 10 cm and focal length of the lens is 30 cm ?

Options

A. `(6)/(5)`
B. `(7)/(4)`
C. `(2)/(3)`
D. `(4)/(3)`

Answer

D

Explanation

According to lens maker.s formula,
`(1)/(f)=(mu-1)((1)/(R_(1))-(1)/(R_(2)))`
Here, f= `30` cm, `R_(1)=oo` (For plane surface), `R_(2)=-10` cm
`:. (1)/(30)=(mu-1)((1)/(oo)-(1)/(-10))implies(1)/(30)=((mu-1))/(10)`
`3(mu-1)=1implies3mu=4impliesmu-(4)/(3)`