Explain why, the sun can be seen about two minutes before actual sunrise. Draw a diagram to illustrate your answer?

Why does the sky appear blue on a clear day?

A person needs a lens of power, -5.5 dioptres for correcting his distant vision. For correcting his near vision, he needs a lens of power, +1.5 dioptres. What is the focal length of the lens required for correcting

1. Distant vision, and
2. Near vision?

Why does the Sun appear reddish early in the morning?

Name the cells on the retina of an eye which are sensitive to

1. Dright light.
2. Dim light.
3. Sensation of colour.

The power of a lens is +1.5D. Name the type of defects vision that can be corrected by using this lens. Find the focal length of the lens.

In a certain murder investigation, it was important to discover whether the victim was long-sighted or short-sighted. How could a detective decide by examining his spectacles?

Explain why, if we look at objects through the hot air over a fire, the objects appear to be moving (or shaking) slightly.

The eyes of a person are focused

1. On a nearby object, and
2. On a distant object, turn by turn. In which case:

1. The focal length of ye-lens will be the maximum?
2. The converging power of eye-lens will be the maximum?

What happens to the image distance in the eye when we increase the distance of an object from the eye?