Question

Find the focal length of a thin plano-convex lens. The front surface of this lens is flat, and the rear surface has a radius of curvature of R2 = -35 cm. Assume that the index of refraction of the lens is 1.5.

a. -15 cm
b. -25 cm
c. -20 cm
d. -30 cm

Answer 1

The focal length of the thin plano-convex lens is -30 cm.

Step-by-step explanation:

A plano-convex lens has one flat surface and one curved surface. The focal length of the lens can be found using the lens maker's equation:

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

Where:

• f represents the focal length
• n represents the index of refraction
• R1 represents the radius of curvature of the flat surface (which is infinity for a flat surface)
• R2 represents the radius of curvature of the curved surface

Plugging in the given values, we get:

1/f = (1.5 - 1) * (1/infinity - 1/(-35 cm))

Simplifying it further, we get:

f = -30 cm

Therefore, the focal length of the thin plano-convex lens is -30 cm, option d.