Write any four applications of lenses.

Copy the figure and complete it to show the formation of image of the object AB. Name the lens used.

The figure shows a convex  and a concave lens of focal lengths $+20 \mathrm{cm}, -30 \mathrm{cm}$ respectively, their lenses in contact. What is the power of each lens? What is the focal length of the combined lens?

Figure shows a point source of light $20 \mathrm{cm}$ in front of a convex lens of focal length $10 \mathrm{cm}$. What is the final position of the image? Show by a ray diagram.