The refractive index of a material of a plano-concave lens is `5/3`, the radius of curvature is 0.3 m. The focal length of the lens in air is

Options

A. -0.45 m
B. -0.45 m
C. -0.75 m
D. -1.0 m

Answer

A

Explanation

From the Lens Maker's formula,
`1/f =-(mu-1)(1/R_(1) – 1/R_(2))`
` implies 1/f =-(5/3 -1)(1/0.3 – 1/infty)`
`implies 1/f=(-2)/3 xx 1/0.3`
`therefore f=-0.45m`