Question

A biconvex lens made of transparent material of refractive index 1.5 and the radii of curvature of the faces of the double convex lens are 20 cm each

(i) calculate the focal length of the lens.
(ii) what will be its new focal length when placed in a medium of refractive index 1.2 and 1.65 ? will the lens behave a converging or diverging lens ? give reason.'

Answer 1

The focal length of the biconvex lens is 0 cm, meaning it does not converge or diverge light.

Step-by-step explanation:

To calculate the focal length of the biconvex lens, we can use the lens maker's equation:

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

where f is the focal length, n is the refractive index, R1 is the radius of curvature of the first face, and R2 is the radius of curvature of the second face.

Substituting the given values, we get:

f = (1.5 - 1) * (1 / 20 - 1 / 20) = 0.5 * (0 - 0) = 0

The calculated focal length is 0 cm. This means that the lens is not a converging or diverging lens, but rather a plano lens that does not converge or diverge light.