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

Answer

A

Explanation

`(1)/(f) = (n_(ag) -1) ((1)/(R_(1)) - (1)/(R_(2)) )`
`rArr " " (1)/(f) = ((2)/(3) -1) ((1)/(10) + (1)/(10) )`
`rArr (1)/(f) = (-1)/(3) xx (2)/(10) rArr f = 15 ` cm .
Hence, behave as concave lens.