Focal length of convex lens will miximum for

Options

A. blue light
B. yellow light
C. red light
D. green light

Answer

A

Explanation

`(1)/(f)=(n-1)((1)/(R_(1))-(1)/(R_(2)))=K(n-1)`
`therefore f prop (1)/(R.I.(n))`
In the visible spectrum, VIBGYOR,
`n_(B) gt n_(G) gt n_(Y) gt n_(R )`
As `n_(B)` is maximum, the focal length is minimum for blue light.