Explain with the help of a diagram, how we are able to observe the sunrise about two minutes before the sun gets above the horizon.

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?

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.

A man can read the number of a distant bus clearly but he finds difficulty in reading a book.A man can read the number of a distant bus clearly but he finds difficulty in reading a book.

1. From which defect of the eye is he suffering?
2. What type of spectacle lens should he use to correct the defect?

Why are the ‘danger signal’ lights red in colour?

Explain why, when the sun is overhead at noon, it appears white, but when the same sun is near the horizon at sunset, it appears red?

What happens to the eye when you enter a darkened cinema hall from bright sunshine? Give reason for your answer.

What are rods and cones in the retina of an? Why is our night vision relatively poor compared to the night vision of an owl?

How is the amount of light entering the eye controlled?

Complete the following statements:
When the sun is setting, the light from it has to travel a ____ thickness of the earth's atmosphere and only ____ wavelength _____ light is able to reach us. Sunset is therefore ___.