Question: Q. 5. Answer the following questions :
(i) Why is the thin ozone layer on top of the stratosphere crucial for human survival ? Identify to which part of electromagnetic spectrum does this radiation belong and write one important application of the radiation.
(ii) Why are infrared waves referred to as heat waves? How are they produced? What role do they play in maintaining the earth’s warmth through the greenhouse effect?
U[Delhi I, II, III 2015]
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Solution:
Ans. (i) It absorbs ultraviolet radiations from sun and prevents them from reaching on the earth’s surface causing damage to life.
Identification : Ultraviolet radiations
One correct application : Sanitization, Forensics $1 / 2$ (ii) Water molecules present in most materials readily absorbs infra red waves. Hence, their thermal motion increases, therefore, they heat their surroundings.
$1 / 2$ They are produced by hot bodies and molecules. $1 / 2$ Incoming visible light is absorbed by earth’s surface and radiated as infrared radiations. These radiation are trapped by green house gases.
$1 / 2$
[A] Q. 6. Identify the type of waves which are produced by the following way and write one application for each :
(i) Radioactive decay of the nucleus.
(ii) Rapid acceleration and decelerations of electrons in aerials.
(iii) Bombarding a metal target by high energy $\begin{array}{ll}\text { electrons. } & R \text { [CBSE SQP 2015-2016] }\end{array}$
Ans.
| S. No. | Type of wave | Application |
|---|---|---|
| (i) | Gamma rays | Treatment of tumors |
| (ii) | Radio waves | Radio and television Communication system |
| (iii) | X-rays | Study of crystals |
[CBSE Marking Scheme 2016]
