Question

A plano-convex lens is made of material of refractive index 1.6. The radius of curvature of the curved surface is 60 cm. The focal length of the lens is(a) 50 cm(b) 100 cm(c) 200 cm(d) 400 cm

Answer 1

(B) 100 CM IS THE ANSWER

Answer 2

Answer:

B) 100cm

Explanation:

Refractive Index = 1.6 (Given)

Radius of curvature = 60cm (Given)

R1 = +∞

R2 = -60cm

The relation of the focal length of a lens and the radius of curvatures is given by the lens maker equation -

1/f = (u2-u1-1)(1-R1-1/R2)

Thus, the focal length will be denoted as-

1/f = (u-1) [1/R1-1/R2]

1/f = (1.6-1) [1/∞ - 1/-60]

or f = 100cm

Therefore, the focal length of the lens will be 100cm