Question

Find the radii of curvature of a convex and concave convergent lens made of glass of refractive index n-1.5 having focal leangth of 24cm if R2 =2R1​

Answer 1

Answer:

Explanation:

Given: a convexo-concave convergent lens made of pf glass with refractive index, ν=1.5 and focal length, f=24cm. It has one of the radii of curvature is double the other

To find its radii of the curvature

Solution:

According to the given criteria,

R1 =2R2

for convexo-concave lens R1 is positive and R2  is positive

According to the lens maker formula, 1/f  =(n−1)(1/R 1−1/R2 ) ⟹ 1/24 =(1.5−1)(1/R 1 −1/R2) ⟹ 1/ 24×0.5  =  2-1/2R 1

⟹R  1 =   12/2 =6cm

∴,R  2 =2R  1 =12cm

Hence the radii of the curvature is 6cm and 12cm