Question

An object 50 cm tall is placed on the principal axis of a convex lens, its 20 cm tall image is formed on the screen placed at a distance of 10 cm from the lens. Calculate the focal length of the lens.

Answer 1

The lens formula is 1/f = 1/v - 1/u. The magnification formula is -v/u = h'/h.

From the magnification formula, we get v = -20/50 * u. Substituting this into the lens formula gives us 1/f = -50/20 * 1/u - 1/u. Solving this equation for f will give you the focal length of the lens.