## Solutions of The Human Eye and The Colourful World Lakhmir Singh Manjit Kaur LAQ, MCQ, HOTS, VSAQ and SAQ Pg No. 289 Class 10 Physics

27A. Draw a diagram to show the refraction of light through a glass prism. On this diagram, mark (i) incident ray (ii) emergent ray, and (iii) angle of deviation.

27B. What is a rainbow? What are the two conditions necessary for the formation of a rainbow in the sky?

→ An arch of seven colors visible in the sky which is produced by the dispersion of sun's light by raindrops in the atmosphere is known as rainbow. The two conditions necessary for the formation of the rainbow are:-
I) there should must be a shining sun in the sky,
II) it should must be raining at the same time.

27C. What acts as tiny prisms in the formation of a rainbow?

→ Raindrops act as tiny prisms in the formation of a rainbow.

27D. Name the process which is involved in the formation of a rainbow.

→ The process which is involved in the formation of a rainbow is known as dispersion of light.

27E. What are the seven colours seen in a rainbow?

→ The seven colors seen in a rainbow are Red, Orange, Yellow, Green, Blue, Indigo and Violet.

Multiple Choice Questions (MCQs)-Pg-289

28. A beam of white light is shone onto a glass prism. The light cannot be:
A. deviated
B. dispersed
C. focused
D. refracted

→ A beam of white light is shone onto a glass prism. The light cannot be focused.

29. A beam of white light falls on a glass prism. The colour of light which undergoes the least bending on passing through the glass prism is :
A. violet
B. red
C. green
D. blue

→ A beam of white light falls on a glass prism. The colour of light which undergoes the least bending on passing through the glass prism is red.

30. The colour of white light which suffers the maximum bending (or maximum refraction) on passing through a glass prism is :
A. yellow
B. orange
C. red
D. violet

→ The color of white light which suffers the maximum bending (or maximum refraction) on passing through a glass prism is violet.

31. Which of the following colour of white light is least deviated by the prism?
A. green
B. violet
C. indigo
D. yellow

→ Yellow color of white light is least deviated by the prism.

32. The colour of white light which is deviated the maximum on passing through the glass prism is:
A. blue
B. indigo
C. red
D. orange

→ The colour of white light which is deviated the maximum on passing through the glass prism is indigo.

33. The splitting up of white light into seven colours on passing through a glass prism is called :
A. refraction
B. deflection
C. dispersion
D. scattering

→ The splitting up of white light into seven colours on passing through a glass prism is called dispersion.

34. Which of the following coloured light has the least speed in glass prism ?
A. violet
B. yellow
C. red
D. green

→ Violet colored light has the least speed in glass prism.

35. The coloured light having the maximum speed in glass prism is :
A. blue
B. green
C. violet
D. yellow

→ The yellow colored light having the maximum speed in glass prism.

36. Which of the following colour of white light has the least wavelength?
A. red
B. orange
C. violet
D. blue

→ Violet color of white light has the least wavelength.

37. Out of the following, the colour of light having the maximum wavelength is:
A. violet
B. indigo
C. green
D. orange

→ The color of light having the maximum wavelength is orange.

Questions Based on High Order Thinking Skills (HOTS)-Pg-290

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

→ Due to the parallel sides of the flat plane glass we do not see a spectrum of colors when light passes through a flat pane of glass.

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

→ (a) White paper reflects all the colors in sunlight.
(b) Blackboard absorb all the colors in sunlight.

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

→ White sunlight may be made of different colors can be evidenced in the nature during the formation of rainbow in the sky.

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

→ The phenomenon which causes the twinkling of stars is atmospheric refraction of light.

2. Name two effects produced by the atmospheric refraction.

→ The two effects produced by the atmospheric refraction are:-
1) Twinkling of stars
2) Advance sunrise and delayed sunset.

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

→ (a) The phenomenon which makes us see the sun a few minutes before actual sunrise is atmospheric refraction of light.
(b) The phenomenon which makes us see the sun a few minutes after actual sunset is atmospheric refraction of sunlight.

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

(b) Atmospheric refraction causes delayed sunset is by about 2 minutes.

5. State whether the following statement is true or false:
The planets twinkle at night due to atmospheric refraction of light.

→ False, the stars twinkle at night due to atmospheric refraction of light.

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

→ The phenomenon due to which the stars seem higher in the sky than they actually is atmospheric refraction of sunlight.

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...............

→ We can see the sun about two minutes before the actual sunrise and about two minutes after the actual sunset because of atmospheric refraction.

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

→ Because of atmospheric refraction of light coming from the star while passing through the successive denser layers of earth's atmosphere stars seem higher than they actually are. It can be illustrated through a diagram:-

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

→ Because of atmospheric refraction of sun's light the sun can be seen about two minutes before actual sunrise. When the sun is slightly below the horizon, then the sun's light coming from less dense air to more dense air is refracted downwards as it passes through the atmosphere and the appears to be raised above the horizon.
Let us see a diagram to illustrate it:-

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

→ When we look at objects through the hot air over a fire, the objects appear to be moving (or shaking) slightly this happens because 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.

11A. What is atmospheric refraction? What causes atmospheric refraction?

→ When the refraction of light takes place due to the atmosphere is known as atmospheric refraction. Due to the varying optical densities of different layers of earth's atmosphere atmospheric refraction takes place.

11B. Why do stars twinkle on a clear night ?

→ When the light from stars reaches us it has to travel through the different layers of the earth’s atmosphere. Due to the 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.

11C. Explain why, the planets do not twinkle at night.

→ As the planets are near to earth so they appear big and so they have a collection of many 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. That is why, the overall brightness remains the same and the planets do not appear to twinkle.

Multiple Choice Questions (MCQs)-Pg-292

12. The twinkling of stars is due to atmospheric:
A. reflection of light
B. dispersion of light
C. interference of light
D. refraction of light

→ The twinkling of stars is due to atmospheric refraction of light.

13. The atmospheric refraction of light causes the twinkling of:
A. planets only
B. stars only
C. planets and stars
D. stars and satellites

→ The atmospheric refraction of light causes the twinkling of stars only.

14. The stars appear higher in the sky than they actually are, due to:
A. diffraction of light
B. scattering of light
C. refraction of light
D. reflection of light

→ The stars appear higher in the sky than they actually are, due to refraction of light.

15. The stars twinkle but the planets do not twinkle at night because:
A. the stars are small but the planets are large
B. the stars are very large but planets are small
C. the stars are much nearer but planets are far off
D. the stars are far off but planets are nearer to earth

→ The stars twinkle but the planets do not twinkle at night because the stars are far off but planets are nearer to earth.

16. As light from a far off star comes down towards the earth:
A. it bends away from the normal
B. it bends towards the normal
C. it does not bend at all
D. it is reflected back

→ As light from a far off star comes down towards the earth it bends towards the normal.

17. We can see the sun before the actual sunrise by about:
A. 5 minutes
B. 2 minutes
C. 2 hours
D. 20 minutes

→ We can see the sun before the actual sunrise by about 2 minutes.

18. Due to atmospheric refraction of sunlight, the time from sunrise to sunset is lengthened by about:
A. 6 minutes
B. 2 minutes
C. 4 minutes
D. 5 minutes

→ Due to atmospheric refraction of sunlight, the time from sunrise to sunset is lengthened by about 4 minutes.

19. The day is longer on the earth by about 4 minutes because:
A. the earth is round in shape
B. the earth rotates on its axis
C. the earth revolves around the sun
D. the earth has atmosphere

→ The day is longer on the earth by about 4 minutes because the earth has atmosphere.

Questions Based on High Order Thinking Skills (HOTS)-Pg-293

20. We know that light refracts (or bends) when it goes from one medium to another. Now, the atmosphere contains only air. Then how does light get refracted on passing through only air in the atmosphere?

→ We know that light refracts (or bends) when it goes from one medium to another. Now, the atmosphere contains only air but still refraction occurs this is due to the reason that all the air present in the atmosphere is not at same temperature. Some of the air layers are cold whereas others are comparatively warm. The cooler air layers of the atmosphere behave as optically denser medium for the light rays whereas the warmer air layers behave as optically rarer medium.

21. By how much time the day would have been shorter if the earth had no atmosphere?

→ By about 4 minutes the day would have been shorter if the earth had no atmosphere.

22. A student claims that because of atmospheric refraction, the sun can be seen after it has set, and the day is, therefore, longer than if the earth had no atmosphere.
(a) What does the student mean by saying that the sun can be seen after it has set?
(b) Do you think that the students' conclusion is correct?

→ The student mean by saying that the sun can be seen after it has set, is due to the atmospheric refraction we continue to see the sun about two minutes after the actual sunset. This is because earth has atmosphere which cause refraction and this is the reason for having longer day.
(b) Yes, the students conclusion is correct.

1. What is the colour of the sunlight:
(a) scattered by the dust particles in the atmosphere?
(b) scattered by the air molecules in the atmosphere?

→ (a) The color of the sunlight scattered by the dust particles in the atmosphere is white.

(b) The color of the sunlight scattered by the air molecules in the atmosphere is blue.

2. Which of the two is scattered more easily: light of shorter wavelengths or light of longer wavelengths?

→ Light of shorter wavelengths scatters more easily.

3. State whether the following statements are true or false:
(a) The scattering away of red light makes the sky appear blue during the day time.
(b) The scattering away of blue light makes the sun appear red at sunset.

→ (a) False, The scattering away of blue light makes the sky appear blue during the day time
(b) True, The scattering away of blue light makes the sun appear red at sunset.

4. What colour does the sky appear to an astronaut?

→ Dark (or black) color appear to the astronaut.

5. Which effect is illustrated by the observation that when a beam of sunlight enters a dusty room, then its path becomes visible to us.

→ Tyndall effect is illustrated by the observation that when a beam of sunlight enters a dusty room, then its path becomes visible to us.

6. State two effects produced by the scattering of light by the atmosphere.

→ The two effects produced by the scattering of light by the atmosphere are:-
1) Sky appears blue
2) Sun appears red at sunrise and sunset.

7. What is tyndall effect? Explain with an example.

→ Tyndall effect (scattering of light) is the scattering of light by particles in its path.

Example. When through a window, sunlight enters a dusty room then its path becomes visible to us due to the scattering of the light by the dust particles present in the air.

8. What happens when a beam of sunlight enters a dusty room through a window ? Explain your answer.

→ The path of the light become visible to us, when a beam of light enters a dusty room through a window. The tiny dust particles present in the air of room scatter the beam of light all around the room.

9. Why does the sky appear blue on a clear day ?

→ The scattering of blue component of white sunlight by air molecules presents in the atmosphere cause the sky to look blue during a clear day. When sunlight passes through the atmosphere, most of the longer wavelength lights do not get scattered much and hence pass straight through the atmosphere. The shorter wavelength blue light is, however, scattered all around the sky and whichever direction we look, some of this scattered blue light enters our eyes.

10. Why does the sky appear dark (or black) to an astronaut instead of blue?

→ The sky appear dark (or black) to an astronaut instead of blue because in the outer space there is no atmosphere which contains air due to which there is no scattering of light takes place. And when there is no scattered light to reach our eyes in outer space, therefore the sky looks dark and black there.

11. Why does the sun appear red at sunrise ?

→ At the sunrise the sun and the surrounding appears to be red because at that time most of the blue color present in sunlight has been scattered out and away from our line of sight, leaving behind mainly red color in the direct sunlight beam that reaches our eyes.

12. Why does the sun appear red at sunset ?

→ During the sunset the sun and the surrounding appears to be red, the reason is, at that time most of the blue color present in sunlight has been scattered out and away from our line of sight, leaving behind mainly red color in the direct sunlight beam that reaches our eyes.

13. Why are the 'danger signal' lights red in colour?

→ The red colored light having longer wavelength is the least scattered by fog or smoke particles. Due to this the red light can be seen in the same color even from a distance. This is the reason why ‘Danger’ signals are red in color.

14A. Draw a neat and labelled diagram of the experimental set up for observing the scattering of light in a colloidal solution of sulphur to show how the sky appears blue, and the sun appears red at sunrise and sunset.

→ A neat and labelled diagram of the experimental set up for observing the scattering of light in a colloidal solution of sulphur to show how the sky appears blue, and the sun appears red at sunrise and sunset is shown below:-

14B. Out of blue light and red light, which one is scattered more easily?

→ Blue light scattered more easily.

4C. Which component of sunlight is scattered away when the sun appears red at sunrise or sunset?

→ Blue component of sunlight is scattered away when the sun appears red at sunrise or sunset.

14D. What causes the scattering of blue component of sunlight in the atmosphere?

→ The scattering of blue component of sunlight in the atmosphere is caused by the gas molecules present in the air.

Multiple Choice Questions (MCQs)-Pg-298

15. The blue colour of sky is due to:
A. refraction of light
B. diffraction of light
C. dispersion of light
D. scattering of light

→ The blue colour of sky is due to scattering of light.

16. The red colour of the sun at the time of sunrise and sunset is because:
A. red colour is least scattered
B. blue colour is least scattered
C. red colour is most scattered
D. blue colour is most scattered

→ The red color of the sun at the time of sunrise and sunset is because the blue color is most scattered.

17. Which of the following is not caused by the atmospheric refraction of light?
A. twinkling of stars at night
B. sun appearing higher in the sky than it actually is
C. sun becoming visible two minutes before actual sunrise
D. sun appearing red at sunset

→ Sun appearing red at sunset is not caused by the atmospheric refraction of light.

18. The sky appears blue because some of the blue component of sunlight is scattered by:
A. gas molecules present in air
B. dust particles present in air
C. water droplets suspended in air
D. soot particles present in air

→ The sky appears blue because some of the blue component of sunlight is scattered by gas molecules present in air.

19. Sunset is red because at that time the light coming from the sun has to travel:
A. lesser thickness of earth's atmosphere
B. greater thickness of earth's atmosphere
C. varying thickness of earth's atmosphere
D. along the horizon

→ Sunset is red because at that time the light coming from the sun has to travel greater thickness of earth's atmosphere.

Questions Based on High Order Thinking Skills (HOTS)-Pg-298

20. In an experiment to study the scattering of light by passing a beam of white light through a colloidal solution of sulphur in a transparent glass tank :
(a) Which colour is observed from the front of the glass tank? Does this colour correspond to the colour of sky on a clear day or the colour of sky around the sun at sunset ?
(b) Which colour is observed from the sides of the glass tank? Does this colour correspond to the colour of sky on a clear day or the colour of sky around the sun at sunset ?

→ (a) Red color is observed from the front of the glass tank. This color correspond to the color of sky around the sun at sunset.

(b) Blue color is observed from the sides of the glass tank. This color correspond to the color of sky on a clear day.

21. Explain why, when the sun is overhead at noon, it appears white, but when the same sun is near the horizon at sunset, it appears red.