A convex lens of focal length is 2/3 times R . find refractive index of the material

Given:

A convex lens of focal length is 2/3 times R

We need to find the refractive index of the material

Solution:

From Lens makers formula we know that

1/f = (n – 1) (1/R1 – 1/R2) ———————(i) { were n is refractive index}

We know that

For biconvex lens

R1 = + R and R2 = – R

f= 2/3 R (Given)

Substituting the value of from the above equation in equation (i) we get,

1/ 2/3 R= (n-1) ( 1/ R – 1/ -R)

3/2R = (n -1) (2/R)

=(n -1) = 3/4

= n = 1 + 3/4

= 7/4

Hence n= refractive index of the material = 3/4

Leave a Comment

Your email address will not be published. Required fields are marked *

BOOK

Free Class