Question

An equiconvex lens has a focal length of 0.1 m and radius of one curved surface is 0.12 m. Find the refractive index of the material of the convex lens.

Answer 1

Given - Focal length - 0.10 metre

Radius of curvature - 0.12 metre

Equiconvex lens

Find - Refractive Index of material of convex lens.

Solution - Lens maker's equation holds relationship between refractive index, focal length and radii of curvature of the two spheres used in lenses.

The equation is -

1/f = (meu-1) {(1/R1)-(1/R2)}

In the equation, f stands for focal length, meu is refractive index, R1 and R2 refers to radius of curvature.

Since question states lens to be equiconvex hence, R1 = R2 = R.

Therefore, new formula will be,

1/f = (meu-1)*(2/R)

Keeping values in equation-

1/0.10*(0.12/2) = (meu-1)

0.06/0.10 = meu-1

0.6 = meu-1

meu = 1.6

Hence, refractive index of material of convex lens is 1.6.