Question

3. A biconvex lens has a focal length half the radius of
curvature of either surface. What is the refractive
index of lens material ?
(Ans. 2)

Answer 1

Explanation:

f =R/2

2f =R

according to the formula

1/f = (n-1) (1/R1 - 1/R2)

1/f = (n-1) (1/2f - (-1/2f) ( R2= -R2 in case of convex lens)

1/f = (n-1) (2/2f)

1/f = (n-1) (1/f)

(n-1) =1

n =1+1

n= 2