(i) Why the thin ozone layer on the top of the atmosphere is crucial for human survival ? Identify in which part of electromagnetic spectrum does this radiation belong and write an important application of this radiation.
(ii) Why are infrared waves referred to as heat waves ? How are they produced ? What role do they play in maintaining earth.s warmth through the greenhouse effect ?

Which of the following electromagnetic wave play an important role in maintaining the earth's warmth or average temperature through the greenhouse effect?

Assertion : infrared radiation plays an important role in maintaining the average temperature of earth Reason : Infrared radiations are sometimes referred to as heat waves.

Asnwer the following : (a) Name the em waves which are used for the treatment of certain forms of cancer. Write their frequency range. (b) Thin ozone layer on top of stratosphere is crucial for human survival. Why ? (c) Why is the amount of the momentum transferred by the em waves incident on the surface so small?

Rakesh and Rajesh are 8th class students. They are fond of watching cricket match, particularly when it is played between Australia and India. They observed that most of the players, when they are in the field, apply a cream on their face. They did not know its reason. One day they asked this question to their teacher. The teacher thought it to be a good question and explained the reason for applying this cream to the whole class. Based on this paragraph, answer the following questions: (i) In your opinion, what explanation did the teacher offer to the students in the class? (ii) Why is small ozone layer on top of the stratosphere considered crucial for human survival? (iii) Write any two values displayed by Rakesh and Rajesh and their class teacher?