State and define the SI unit of power of a lens.

Does the incident and emergent ray coincide in the process of refraction through glass slab? Give reason.

Which lens would you prefer to use while reading small letters from a dictionary?

Draw ray diagrams showing the image formation by a concave mirror when an object is placed:
Between pole and focus of the mirror.

Light travels more quickly through water than through glass:

1. Which is optically denser: Water or glass?
2. If a ray of light passes from glass into water, which way will it bend: Towards the normal or away from the normal?

A star appears slightly higher (above) than its actual position in the sky illustrate it with the help of a labelled diagram.

A vertical ray of light strikes the horizontal surface of some water:

1. What is the angle of incidence?
2. What is the angle of refraction?

Write the word AMBULANCE as it would appear when reflected in a plane mirror. Why is it sometimes written in this way (as its mirror image) on the front of an ambulance?

‘‘A concave mirror of focal length 15cm can form a magnified erect as well as inverted image of an object placed in front of it.’’ Justify this statement stating the position of the object with respect to the pole of the mirror in both cases for obtaining the images.

With the help of a ray diagram explain why a concave lens diverges the rays of a parallel beam of light.