Question

A convex spherical surface has a radius of curvature 30cm and refractive index 1.5 its first focal length is

Answer 1

The focal length will be 30 cm.

Explanation:

Suppose the radius of curvature of spherical surface convex lens are R1 and R2  respectively

R1 = 30 cm               ( towards right)  

R2 = -30 cm             (towards left)

Refractive index = μ = 1.5

Suppose f is the focal length, then for convex lens:

1/f = (μ-1)(1/R1 - 1/R2)

1/f = (1.5-1)(1/30 -  1/(-30))

1/f = (0.5)(2/30)

1/f = 1/30

f = 30 cm