Give reasons for the following:-
a) Colour of clear sky is blue.
b)Sun can be seen about two minutes before actual sunrise.
c)Traffic light signals are of red colour.
d)Stars appears to twinkle.
e)Planets do not twinkle.
Here is your answer
a.The sky appears blue, when viewed from Earth, because of the scattering of the light. Scattering is the phenomenon by which a beam of light is redirected in many different directions when it interacts with a particle of matter. When sunlight strikes molecules in our atmosphere, the light is redirected in many directions. The blue light is scattered more than the red light because blue color has smallest wave length so it got scattered most and causing the sky to be blue.
b.The Sun is visible to us two minutes before the sunrise and two minutes after the Sunset, because of the bending of the light due to atmospheric refraction. The light from the Sun got refracted by the atmospheric layers and reaches the observer. This causes the observer to think that the light is coming straight from the Sun.
c.Traffic signals are red in colour due to the following reasons-
1.It has the highest wavelenght in all colours and due to its property it is visible from far distance
2.It is least scattered by fog,cloudy weather and translucent situationsd.Stars twinkle because our atmosphere is constantly moving around or is turbulent. The light travelling from the stars gets bent in different direction making them twinkle. It is quite similar to the effect when viewing the reflection of the moon on a lake's surface when its (lake) moving.
e.Planets do not twinkle because they appear larger in size than the stars as they are relatively closer to earth. Planets can be considered as a collection of a large number of point-size sources of light. The different parts of these planets produce either brighter or dimmer effect in such a way that the average of brighter and dimmer effect is zero. Hence, the twinkling effects of the planets are nullified and they do not twinkle.