A narrow beam of light produces a spectrum XY on passing through a triangular glass prism.

1. State the colour at X and Y.
2. Why do the different components of white light bend through different angles with respect to the incident beam of light?

The picture given here shows a person wearing 'half-moon' spectacles. What sort of eye-defect do do you think he has? Why are these particular spectacles useful to him?

A person walking in a dark corridor enters into a brightly lit room:

1. State the effect on the pupil of the eye.
2. How does this affect the amount of light entering the eye?

What are the two most common defects of vision (or defects of eye)? How are they corrected?

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.

Why is a normal eye not able to see clearly the objects placed closer than 25cm?

Name the colour for which angle of deviation while passing through the glass prism is.

1. Maximum.
2. Minimum.

When we place a glass prism in the path of a narrow beam of white light a spectrum is obtained. What happens when a second identical prism is placed in an inverted position with respect to the first prism? Draw a labelled ray diagram to illustrate it.

Write the function of each of the following parts of human eye.

1. Cornea.
2. Iris.
3. Crystalline lens.
4. Ciliary muscles.

A star sometimes appears brighter and some other times fainter. What is this effect called? State the reason for this effect.