If the image formed by a lens is always diminished and erect, what is the nature of the lens?

A lens forms a real image 3 cm high of an object 1 cm high. If the separation of object and image is 15 cm, find the focal length of the lens.

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

Copy and complete the diagram below to show what happens to the rays of light when they pass through the concave lens:

Which type of lenses is?

(a) Thinner in the middle than at the edges?

(B) Thicker in the middle than at the edges?