Question

The radii of curvatures of two convex lenses are 0.05 m and 0.05m. Its refractive index is 1.5. What is its focal length ?

Answer 1

Answer:

Focal length f = 0.05 m

Explanation:

☆Given:

Radius of curvature of convex lens R1 = + 0.05 m

Radius of curvature of convex lens R2 = - 0.05 m

Refractive index μ = 1.5

Find: Focal length of the given convex lens.

☆Solution:

When the refractive index and radii of curvature are known, we can use the Lens maker's formula to find the focal length of the lens.

1/f = (μ - 1) [1/R1 - 1/R2]

1/f = (1.5 - 1) [1/0.05 - 1/(-0.05)]

1/f = 0.5 * [1/0.05 + 1/0.05]

1/f = 0.5 * 2/0.05

1/f = 1/0.05

Therefore focal length f = 0.05 m