Question

student focus the sun rays using an optical device x on a screen is as shown what conclusion can be drawn based on this about device x

Answer 1

Object X is a convex lens of focal length 40cm.

This is evident to the behaviour of the rays.

All rays which are parallel and close to the principal axis are converged to the focal point of the lens.

In our case the rays are diverged 40cm from X which means the focal length of the lens is 40cm.