Will the focal length of a lens for red light be more, same or less than that for blue light ?

Explanation

As the refractive index for red is less than that for blue, parallel beams of light incident on a lens will be bent more towards the axis for blue light compared to red.
In order words ,` mu_(b) gt mu_(r),`
By lens maker's formula
`" " (1)/(f)=(n_(21)-1)((1)/(R_(1))-(1)/(R_(2)))`
Therefore, `f_(b) lt f_(r)`,
Thus, the focal length for blue light will be smaller than that for red.