Browse by Stream
QnA
Home
QnA
Go To Your Study Dashboard

Get Answers to all your Questions

header-bg qa
  • Home
  • NCERT
  • Will the focal length of a lens for red light be more, same or less than that for blue light?

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

 

Answers (1)

The refractive index depends on the colour of light or wavelength of light.

Cauchy's equation : \mu =A+\frac{B}{\lambda ^{2}}+\frac{C}{\lambda ^{4}}+......

As      \lambda _{red}>\lambda _{blue} hence \mu _{red}<\mu _{blue}

Hence parallel beams of light incident on a lens will be bent more towards the axis for blue light compared to red.

By lens maker's formula,

\frac{1}{f}=\left ( \mu -1 \right )\left ( \frac{1}{R_{1}}-\frac{1}{R_{2}} \right )

The refractive index for red light is less than that for blue light, \mu _{red}<\mu _{blue}

Hence \frac{1}{f_{red}}<\frac{1}{f_{blue}}\Rightarrow f_{red}>f_{blue}

Thus, the focal length for red light will be greater than that for blue light.

Posted by

infoexpert23

View full answer

Similar Questions

Latest Question