Define the term principal foci of a convex lens and illustrate your answer with the aid of proper diagrams.

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 convex 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.