Define the term principal foci of a concave lens and show them with the help of proper diagrams.

Draw a diagram to represent the second focus of a concave lens.

Out of the two lenses, one concave and the other convex, state which one will show the divergent action on a light beam. Draw diagrams to illustrate your answer.

Show by a diagram the refraction of two light rays incident parallel to the principal axis on a convex lens by treating it as a combination of a glass slab and two triangular glass prisms.