Solutions of The Human Eyes And The Colorful Wor (Page No- 290 & 292) - Physics By Lakhmir Singh | Extra Documents, Videos & Tests for Class 10 PDF Download

Lakhmir Singh Physics Class 10 Solutions Page No:290

Question 38: Why do you not see a spectrum of colours when light passes through a flat pane of glass ?

Solution : Because a flat pane of glass has parallel sides.

Question 39: Name some everyday objects :
 (a) which reflect all the colours in sunlight
 (b) which absorb all the colours in sunlight

Solution : (a) White Paper
(b) Blackboard

Question 40: Where in nature can you find evidence that white sunlight may be made of different colours ?

Solution : Formation of the rainbow in the sky

Lakhmir Singh Physics Class 10 Solutions Page No:292

Question 1: Name the phenomenon which causes the twinkling of stars.

Solution : Atmospheric refraction of light

Question 2: Name two effects produced by the atmospheric refraction.

Solution : Twinkling of stars; Advance sunrise and delayed sunset

Question 3: Which phenomenon makes us see the sun :
 (a) a few minutes before actual sunrise ?
 (b) a few minutes after actual sunset ?

Solution : (a) Atmospheric refraction of sunlight
(b) Atmospheric refraction of sunlight

Question 4: Atmospheric refraction causes advance sunrise and delayed sunset. By how much time is :
 (a) sunrise advanced ?
 (b) sunset delayed ?

Solution : (a) About 2 minutes
(b) About 2 minutes

Question 5: State whether the following statement is true or false :

The planets twinkle at night due to atmospheric refraction of light.

Solution : False

Question 6: Name the phenomenon due to which the stars seem higher in the sky than they actually are.

Solution : Atmospheric refraction of light

Question 7: Fill in the following blanks with suitable words :
 We can see the sun about……….. minutes before the actual sunrise and about…………. minutes after the actual
 sunset because of atmospheric…………..

Solution : two, two, refraction

Question 8: Why do stars seem higher than they actually are ? Illustrate your answer with the help of a diagram.

Solution : Stars seem higher than they actually are because of atmospheric refraction of light coming from the star while passing through the successive denser layers of earth’s atmosphere.

Question 9: Explain why, the sun can be seen about two minutes before actual sunrise. Draw a diagram to illustrate your answer.

Solution : The sun can be seen about two minutes before actual sunrise because of atmospheric refraction of sun’s light as shown in the following diagram. When the sun is slightly below the horizon, then the sun’s light coming from less dense air to more dense air is refracred downwards as it passes through the atmosphere and the appears to be raised above the horizon.

Question 10: Explain why, if we look at objects through the hot air over a fire, the objects appear to be moving (or shaking) slightly.

Solution : The air just above the fire becomes hotter. This hotter air is optically rarer but the colder air further up is optically denser, so when we see the objects by the light coming from them through hot and cold air layers having different optical densities, then refraction of light takes place randomly due to which the objects appear to be moving slightly.

Question 11: (a) What is atmospheric refraction ? What causes atmospheric refraction ?
 (b) Why do stars twinkle on a clear night ?
 (c) Explain why, the planets do not twinkle at night.

Solution : (a) The refraction of light caused by the earth’s atmosphere is called atmospheric refraction. It is caused due to the varying optical densities of different layers of earth’s atmosphere.
(b) The light coming from a star undergoes atmospheric refraction due to varying optical densities of air at various altitudes. The continuously changing atmosphere refracts the light from the star by different amounts from one moment to the next. Thus, the star-light reaching our eyes increases and decreases continuously and the star appears to twinkle.
(c) Planets appear to be quite big to us and can be considered to be a collection of a very large number of point sources of light. The dimming effect produced by some of the point sources is nullified by brighter effect produced by some other point sources. Thus, the overall brightness remains the same and the planets do not appear to twinkle.