Question

a convex lens, and a convex mirror, (of radius of curvature 20 cm) are placed co-axially with the convex mirror placed at a distance of 30 cm from the lens. for a point object at a distance of 20 cm from the lens, the final image; due to this combination, coincides with the object itself. what is the focal length of the convex lens?

Answer 1

The focal length of the convex lens is infinity.

Step-by-step explanation:

To find the focal length of the convex lens, we can use the lens formula:

1/f = 1/v - 1/u

where f is the focal length, v is the image distance, and u is the object distance.

Given that the final image coincides with the object itself, the image distance v is equal to the object distance u.

Plugging in the values:

1/f = 1/u - 1/u

1/f = 0

Since the right side of the equation is 0, the focal length of the convex lens is infinity.