Question

Observe the optical systems above. Given that all surfaces are made of transparent glass and the dotted surfaces represent plane surface. Which among them can be considered as lenses?

Answer 1

Lens should have at least one curved surface, so that it can converge or diverge the incoming light rays. The first optical system is called convex lens and the second one is concave lens. The third lens is called a plano-concave lens and the fourth one is called a plano-convex lens. The fifth optical system has two plane surfaces, and hence it can't be considered as lens.