Explain with the help of a diagram, why a pencil partly immersed in water appears to be bent at the water surface.

A convex lens of power 5D and a concave lens of power 7.5D are placed in contact with each other. What is the:

1. Power of this combination of lenses?
2. Focal length of this combination of lenses?

State and define the S.I. unit of power of a lens.

An object is placed at a distance of 15 cm from a concave lens of focal length 30 cm. List four characteristics (nature, position, etc.) of the image formed by the lens.

Where must the object be placed for the image formed by a converging lens to be:

1. Real, inverted and smaller than the object?
2. Real, inverted and same size as the object?
3. Real, inverted and larger than the object?
4. Virtual, upright and larger than the object?

What do you understand by the power of a lens? Name one factor on which the power of a lens depends.

Briefly describe how you would find the focal length of a concave mirror quickly but approximately.

“A ray of light incident on a rectangular glass slab immersed in any medium emerges parallel to itself.” Draw labeled ray diagram to justify this statement.

Draw ray diagrams showing the image formation by a concave lens when an object is placed:Between focus and twice the focal length of the lens.

Describe with a suitable diagram, how a convex mirror diverges a parallel beam of light rays. Mark clearly the pole, focus and centre of curvature of convex mirror in this diagram.