In figure, an air lens of radius of curvature of each surface equal to `10 cm` is cut into a cylinder of glass of refractive index `1.5.` The focal length and the nature of lens are

Options

A. ` 15cm` , concave
B. `15 cm,` convex
C. `oo` neither concave nor convex
D. `0`, concave

Answer

A

Explanation

`(1)/(f)=(._(g)mu_(a)-1)((1)/(R_(1))-(1)/(R_(2)))=((2)/(3)-1)((2)/(10))`
`implies f=-15cm,` so behaves as concave lens.