Q17 of 60 Page 1

With the help of a labeled diagram, explain why the sun appears reddish at the sunrise and the sunset.

The sun appears reddish early morning because at that time it is located near to the horizon and light has to pass thick layers of air and travel larger distances before reaching us. Thus, the blue rays having shorter wavelength are scattered and the red rays of longer wavelength reaches our eyes giving sun appearance a reddish color.

Thus, it can be stated that the color of sun that appears to us depends on the position of sun and the distance its rays have to travel. If the rays have to travel longer distances then the shorter wavelength colors get scattered away and longer wavelength color appears.


This phenomenon will not be observed by an observer on the moon because there is no atmosphere on the moon to scatter light.



More from this chapter

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15

(a) Planaria, insects, octopus and vertebrates all have eyes. Can we group eyes of these animals together to establish a common 'evolutionary origin? Justify your answer.

(b) "Birds have evolved from reptiles". State evidence to prove the statement.

 16

To construct a ray diagram we use two rays of light which are so chosen that it is easy to determine their directions after reflection from the mirror. Choose these two rays and state the path of these rays after reflection from a concave mirror. Use these two rays to find the nature and position of the image of an object placed at a distance of 15 cm from a concave mirror of focal length 10 cm.

 18

After the examinations Rakesh with his friends went on a picnic to a nearby park. All friends carried cooked food packed in plastic bags or plastic cans. After eating the food some friends collected the leftover food and plastic bags etc. and planned to dispose them off by burning. Rakesh immediately checked them and suggested to segregate the leftover food and peels of fruits from the plastic materials and respectively dispose them off separately in the green and red dustbins placed in the corner of the park.

(a) In your opinion, is burning plastic an eco-friendly method of waste disposal? Why? State the advantage of the method suggested by Rakesh.


(b) How can we contribute in maintaining the parks and roads neat and clean?

 19

Explain why carbon forms compounds mainly by covalent bond. Explain in brief two main reasons for carbon forming a large number of compounds. Why does carbon form strong bonds with most other elements?