A plano-concave lens is made of glass of refractive index 1.5 and the radius of curvature of its curved face is 100 cm. What is the power of the lens?

Options

A. `+0.5D`
B. `-0.5D`
C. `-2D`
D. `+2D`

Answer

B

Explanation

(b) The refractive index is 1.5 and the rdius of curvature of the curved face is 100 cm =1m and of the plane side is `oo`, hence
`P=1/f=(mu-1)(1/R_(1)-1/R_(2))`
Power of the lend,P`=(1.5-1)(1/oo-1/1)=-0.5D`