Stars and the solar system. — Science STD 8 — Question

Name the point inside the human eye where the image is not visible.

Why do you have to use paper or kerosene oil to start fire in wood or coal?

What name is given to the celestial body which revolves around a planet?

What is metamorphosis? Give two examples of metamorphosis.

What is meant by gravitational force (or force of gravity)? Give its one example.

Name any two devices used in everyday life which work on the existence of atmospheric pressure.

Explain why, we cannot see our surroundings clearly when we enter a darkened cinema hall from bright sunshine but our vision improves after some time.

It was observed that the tadpoles are not growing into adult frogs in a village pond. A scientist who was asked to find the reason for this concluded that the pond water did not contain sufficient amount of a mineral P which could make a hormone Q. The hormone Q can causes a phenomenon R in tadpoles so that they become adult frogs.

1. What are (i) P (ii) Q and (ii) R?
2. Name one human disease which can also be caused due to the deficiency of P in the food and water.

What is a vibration (or an oscillation)? Define 'amplitude' of vibration of an object.

What happens to the size of the pupil of our eye in bright light?