Advance sunrise and delayed sunset.<\/li>\n<\/ol>\nQuestion 54.
\nWhat is the twinkling of stars due to?
\nAnswer:
\nThe twinkling of a star is due to atmospheric refraction of starlight.<\/p>\n
Question 55.
\nExplain why the planets do not twinkle.
\nAnswer:
\nPlanets are very close to us as compared to the distance between stars and earth. They appear as a collection of large number of point-sized sources of light (the reflected light from the sun). These different points produce either brighter or dimmer effect in such a way that the total variation in amount of light entering the eye from all sources averages out to zero. Hence, the twinkling effects of the planets are nullified and they do not twinkle.<\/p>\n
<\/p>\n
Question 56.
\nWhy do stars twinkle?<\/p>\n
OR<\/p>\n
How do stars twinkle? Explain.
\nAnswer:
\nStars may be considered as point-sized sources of light. The starlight that enters the atmosphere undergoes refraction continuously before it reaches the earth. The atmospheric refraction is caused due to varying refractive index of air at different altitudes.<\/p>\n
Since the atmosphere bends starlight towards the normal, the apparent position of the star is slightly different from its actual position. The star appears slightly higher than its actual position when viewed near the horizon.<\/p>\n
This shift in the apparent position of the star is continuous as the physical conditions on the earth’s atmosphere are not stationary. As a result, starlight entering the eye flickers. The star sometimes appears brighter, and at some other time, fainter. This gives the twinkling effect.
\n<\/p>\n
Question 57.
\nStars appear to twinkle but planets do not appear to twinkle. Why?
\nAnswer:
\nPlanets, being larger in size, can be taken as a collection of large number of point-sized objects. The refraction effect of light rays coming from such an extended object will nullify the twinkling effect and hence planets do not twinkle.<\/p>\n
Question 58.
\nHow do you explain early sunrise and delayed sunset?
\nAnswer:
\nSunrise is defined as the moment that the Sun first appears just over the horizon. This means that we can’t see the Sun before it appears above the horizon. However, the Sun is visible to us about two minutes before the actual sunrise, and about two minutes after the actual sunset.<\/p>\n
This is because of the atmospheric refraction of the light from the Sun by the Earth’s atmosphere. Earth’s atmosphere bends the path of the light so that we see the Sun in a position slightly above. Therefore, sun becomes visible before sunrise. Similar things happen during sunset. Therefore, we see the sun for about two minutes even after sunset.<\/p>\n
<\/p>\n
Question 59.
\nThe time difference between the actual subset and the apparent sunset is about two minutes. What is the reason for this? Explain with the help of a diagram.
\nAnswer:
\n
\nWhen the sun has set, the position of the sun appears to have shifted to a slightly higher position due to the refraction of the sun’s light by the atmosphere of the earth. Therefore, the sun would still be visible to us even after it is below the horizon. It is the atmospheric refraction that causes a time difference of about two minutes between actual sunset and apparent sunset.<\/p>\n
Question 60.
\nThe sun becomes visible to us two minutes before actual sunrise. How do you account for this?
\nAnswer:
\n
\nSunrise is defined as the moment that the Sun first appears just over the horizon. Obviously we should not be able to see the sun before it actually rises above the horizon. However, due to refraction of light by the atmosphere, the sun’s apparent position is shifted to a slightly higher point. This makes the sun visible even before sunrise. This explains the time difference of sighting the sun two minutes earlier than actual sunrise.<\/p>\n
Question 61.
\nWhat is meant by scattering of light? Give examples for scattering of light.
\nAnswer:
\nThe phenomenon by which a beam of light is redirected in many different directions when it interacts with a particle of matter is called scattering of light.<\/p>\n
The blue colour of the sky, colour of water in deep sea, the reddening of the sun at sunrise and sunset are due to scattering of light.<\/p>\n
Question 62.
\nWhat is Tyndall effect? Explain with an example.
\nAnswer:
\nThe phenomenon of scattering of light by colloidal particles is called Tyndall effect. The path of a beam of sunlight coming through a window becomes visible due to the scattering of light by the dust particles in the room. This is an instance of Tyndall effect. Similarly, the path of light becomes visible in a smoke-filled room due to Tyndall effect.<\/p>\n
<\/p>\n
Question 63.
\nWhat is the relationship between the size of the scattering particles and the colour of the scattered light?
\nAnswer:
\nFiner particles scatter light of shorter wavelengths (in the blue region) while larger particles scatter light of longer wavelengths (in the red region).<\/p>\n
Question 64.
\nHow do you explain the blue colour of the sky?
\nAnswer:
\nThe sky appears blue when seen from the earth. The blue colour of the sky can be explained on the basis of scattering of light. The molecules present in the atmosphere are ideally suited to scatter blue light. The sky appears blue because we see it through the blue light scattered by the atmospheric air.<\/p>\n
Question 65.
\nWhy does the sky appear dark instead of blue to an astronaut?
\nAnswer:
\nThe sky appears blue because we see it through the blue light scattered by the atmospheric air. However, there is no atmosphere in space to scatter blue light. Hence the sky appears dark to an astronaut.<\/p>\n
Question 66.
\nWhat will be the colour of the sky when it is observed from a place in the absence of any atmosphere? Explain.
\nAnswer:
\nWe see the sky as coloured because the molecules present in our atmosphere interact with the sunlight passing through it and scatter light of certain wavelengths. The type of scattering responsible for blue sky is known as Rayleigh scattering. In the absence of any atmosphere, there will be no scattering of sunlight and hence the sky will appear dark.<\/p>\n
Question 67.
\nWhy does the sun appear reddish at sunrise and sunset?<\/p>\n
OR<\/p>\n
Why does the sun appear reddish early in the mornine?
\nAnswer:
\nThe reddish appearance of the sun at sunrise and sunset can be explained on the basis of scattering of light. During sunrise and sunset, the sun is near the horizon. Therefore, the light of the sun has to pass through thicker layers of air and larger distance in the earth’s atmosphere before reaching our eyes.<\/p>\n
The blue component of sunlight gets almost completely scattered in different directions and the light that reaches our eyes is of longer wavelengths. Therefore, the sun appears reddish during sunrise and sunset.<\/p>\n
<\/p>\n
Question 68.
\nWhy does the Sun appear reddish early in the morning? Explain with the help of a diagram.
\nAnswer:
\n
\nThe molecules in the earth’s atmosphere are ideally suited to scatter blue light. During early morning, the sun is near the horizon. Therefore, the light of the sun will have to pass through denser layers of the atmosphere and over long distances before reaching our eyes.<\/p>\n
During this process, the blue component of sunlight is almost completely scattered away and the light that reaches our eyes is largely in the red region. Therefore, the sun appears reddish during early morning.<\/p>\n
Question 69.
\nWhy does the sun appear white during midday?
\nAnswer:
\nDuring midday, the sun is almost right above us. Therefore, the sunlight will largely pass through less dense regions of the atmosphere and shorter distance before reaching our eyes. Therefore, less amount of blue light present in sunlight is scattered and the light that reaches our eyes has almost all the components of white light. Hence the sun appears white during midday.<\/p>\n
<\/p>\n
Question 70
\nHow do you show experimentally why the sky appears blue and the sun appears reddish during sunrise and sunset?
\nAnswer:
\n
\nPlace a strong source (S) of white light at the principal focus of a converging lens L1<\/sub>. This lens provides a parallel beam of white light. Pass this beam through a sodium thiosulphate solution taken in glass beaker, B. Allow the beam that emerges out of the beaker to pass through a circular hole of a screen. Pass the parallel beam of light that emerges out of the hole through another converging lens L2<\/sub>.<\/p>\nObtain the image of the source on a screen placed at the principal focus of the second lens. The image will be in the form of a whitish circular patch of light. Now add 3 – 5 drops of concentrated sulphuric acid to the sodium thiosulphate solution and stir.<\/p>\n
Keep observing the solution and the image formed on the screen. The solution gradually turns blue due to the scattering of blue light by the particles of the solution. The whitish patch of light on the screen gradually turns to red because the light that reaches the screen is almost free of blue light. After some time, the image disappears from the screen. This explains the blue colour of the sky and the reddish appearance of the sun during sunrise and sunset.<\/p>\n
Question 71.
\nWater mixed with milk is taken in beaker \u2018A \u2019 and sugar solution is taken in beaker \u2018B \u2019. Light is passed through both the beakers. In which beaker is the path of light visible? Why?
\nAnswer:
\nThe path of light is visible in beaker \u2018A\u2019 that contains milk. Milk is a colloidal solution that scatters light. When a beam of light strikes the particles of milk, the path of the beam becomes visible, i.e., scattering of light by colloidal particles gives rise to Tyndall effect.<\/p>\n
<\/p>\n
Fill In The Blanks<\/span><\/p>\n1. The screen of the human eye is called retina<\/span>
\n2. The ability of the eye to adjust the focal length of its lens is called accommodation<\/span>
\n3. The near point of a normal adult eye is 25 cm<\/span>
\n4. Breaking up of the constituent colours of composite light is called dispersion<\/span>
\n5. The defect of the eye due to which nearby objects cannot be seen clearly, is called hypermetropia \/ longsightedness<\/span>
\n6. Myopia can be corrected with spectacles fitted with suitable concave lens<\/span>
\n7. The constituent colour of white light that has the highest wavelength is red<\/span><\/p>\nMultiple Choice Questions<\/span><\/p>\nQuestion 1.
\nThe human eye can focus objects at different distances by adjusting the focal length of the eye lens. This is due to
\n(A) presbyopia.
\n(B) accommodation.
\n(C) near-sightedness.
\n(D) far-sightedness.
\nAnswer:
\n(B) accommodation.<\/p>\n
<\/p>\n
Question 2.
\nThe human eye forms the image of an object at its
\n(A) cornea.
\n(B) iris.
\n(C) pupil.
\n(D) retina.
\nAnswer:
\n(D) retina.<\/p>\n
Question 3.
\nThe least distance of distinct vision for a young adult with normal vision is about
\n(A) 25 m.
\n(B) 2.5 cm.
\n(C) 25 cm.
\n(D) 2.5 m.
\nAnswer:
\n(C) 25 cm.<\/p>\n
Question 4.
\nThe change in focal length of an eye lens is caused by the action of the
\n(A) pupil.
\n(B) retina.
\n(C) ciliary muscles.
\n(D) iris.
\nAnswer:
\n(C) ciliary muscles.<\/p>\n
<\/p>\n
Question 5.
\nScattering of light by particles involves
\n(A) change in direction of light
\n(B) dispersion
\n(C) reflection
\n(D) refraction
\nAnswer:
\n(A) change in direction of light<\/p>\n
Question 6.
\nWhich of the following phenomena of light are involved in the formation of a rainbow?
\n(A) Dispersion, scattering and total internal reflection
\n(B) Reflection, dispersion and total internal reflection
\n(C) Reflection, refraction and dispersion
\n(D) Refraction, dispersion and total internal reflection
\nAnswer:
\n(D) Refraction, dispersion and total internal reflection<\/p>\n
Question 7.
\nA person has an elongated eyeball and hence is suffering from shortsightedness. He requires spectacles fitted with
\n(A) convex lens to focus distant objects
\n(B) concave lens to focus distant objects
\n(C) convex lens to focus near objects
\n(D) concave lens to focus near objects.
\nAnswer:
\n(B) concave lens to focus distant objects<\/p>\n
Question 8.
\nAt noon, the sun appears white as
\n(A) light is least scattered
\n(B) all the colours of the white light are scattered away
\n(C) blue colour is scattered the most
\n(D) red colour is scattered the most
\nAnswer:
\n(A) light is least scattered<\/p>\n
Question 9.
\nThe bluish colour of water in deep sea is due to
\n(A) the presence of algae and other plants found in water
\n(B) scattering of light
\n(C) reflection of sky in water
\n(D) absorption of light by the sea
\nAnswer:
\n(B) scattering of light<\/p>\n
<\/p>\n
Question 10.
\nTwinkling of stars is due to atmospheric
\n(A) dispersion of light by water droplets
\n(B) internal reflection of light by clouds
\n(C) refraction of light by different layers of atmospheric air
\n(D) scattering of light by dust particles
\nAnswer:
\n(C) refraction of light by different layers of atmospheric air<\/p>\n
Question 11.
\nThe clear sky appears blue because
\n(A) blue light gets absorbed in the atmosphere
\n(B) lights of all other colours are scattered more than violet and blue colour lights by the atmosphere
\n(C) ultraviolet radiations are absorbed in the atmosphere
\n(D) violet and blue lights get scattered more than lights of all other colours by the atmosphere
\nAnswer:
\n(D) violet and blue lights get scattered more than lights of all other colours by the atmosphere<\/p>\n
Question 12.
\nThe danger signals installed at the top of tall buildings are red in colour. These can be easily seen from a distance because among all the colours, red light
\n(A) is scattered the most by smoke or fog
\n(B) is scattered the least by smoke or fog
\n(C) is absorbed the most by smoke or fog
\n(D) moves fastest in air
\nAnswer:
\n(B) is scattered the least by smoke or fog<\/p>\n
Question 13.
\nDispersion is a phenomenon involving
\n(A) refraction of light
\n(B) reflection of coloured light
\n(C) combining of coloured lights into white light
\n(D) separation of light into its spectrum
\nAnswer:
\n(B) reflection of coloured light<\/p>\n
<\/p>\n
Question 14.
\nBecause of atmospheric refraction, the Sun actually sets
\n(A) after we see it disappear
\n(B) before we see it disappear
\n(C) when it just disappears
\n(D) hours before we see it disappear
\nAnswer:
\n(B) before we see it disappear<\/p>\n
Question 15.
\nWhich of the following statements is correct?
\n(A) A person with myopia can see distant objects clearly.
\n(B) A person with hypermetropia can see nearby objects clearly.
\n(C) A person with myopia can see nearby objects clearly.
\n(D) A person with hypermetropia cannot see distant objects clearly.
\nAnswer:
\n(C) A person with myopia can see nearby objects clearly.<\/p>\n
Question 16.
\nThe colour of light that refracts most on entering a glass prism is
\n(A) yellow
\n(B) violet
\n(C) blue
\n(D) red
\nAnswer:
\n(D) red<\/p>\n
Question 17.
\nWhich of the following colours of light is least scattered by fog, dust or smoke? .
\n(A) Violet
\n(B) Blue
\n(C) Red
\n(D) Yellow
\nAnswer:
\n(C) Red<\/p>\n
<\/p>\n
Question 18.
\nA person cannot see distinctly objects kept beyond 2 nu This defect can be corrected by using a lens of power
\n(A) +0.2 D
\n(B) -0.2 D
\n(C) +0.5 D
\n(D) -0.5 D
\nAnswer:
\n(D) -0.5 D<\/p>\n
Question 19.
\nRed coloured light is used in traffic signals to indicate the vehicles to stop, because compared to other colours red light
\n(A) has high frequency
\n(B) scatters more
\n(C) has less wavelength
\n(D) scatters less
\nAnswer:
\n(D) scatters less<\/p>\n
Question 20.
\nThe characteristic of the image of an object formed on the retina by the lens of the eye is
\n(A) real and inverted
\n(B) virtual and erect
\n(C) real and erect
\n(D) virtual and inverted
\nAnswer:
\n(A) real and inverted<\/p>\n
<\/p>\n
Match The Following<\/span><\/p>\nQuestion 1.<\/p>\n
\n\n\nColumn A<\/td>\n | Column B<\/td>\n<\/tr>\n |
\n1. Rainbow<\/td>\n | a. Bouncing back of light from a surface<\/td>\n<\/tr>\n |
\n2. Tyndall effect<\/td>\n | b. Causes blue colour of the sky<\/td>\n<\/tr>\n |
\n3. Myopia<\/td>\n | c. Caused by dispersion of light<\/td>\n<\/tr>\n |
\n4. Hypermetropia<\/td>\n | d. Scattering of light by colloidal particles<\/td>\n<\/tr>\n |
\n5. Scattering of light<\/td>\n | e. Cannot see nearby objects clearly<\/td>\n<\/tr>\n |
\n<\/td>\n | f. Cannot see distant objects clearly<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Answer: \n1 – c, 2 – d, 3 – f, 4 – e, 5 – b.<\/p>\n","protected":false},"excerpt":{"rendered":" Students can download Class 10 Science Chapter 11 Human Eye and Colourful World Important Questions, KSEEB SSLC Class 10 Science Important Questions and Answers helps you to revise the complete Karnataka State Board Syllabus and score more marks in your examinations. Karnataka SSLC Class 10 Science Important Chapter 11 Human Eye and Colourful World Question …<\/p>\n","protected":false},"author":6,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[3],"tags":[],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/kseebsolutions.guru\/wp-json\/wp\/v2\/posts\/26857"}],"collection":[{"href":"https:\/\/kseebsolutions.guru\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/kseebsolutions.guru\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/kseebsolutions.guru\/wp-json\/wp\/v2\/users\/6"}],"replies":[{"embeddable":true,"href":"https:\/\/kseebsolutions.guru\/wp-json\/wp\/v2\/comments?post=26857"}],"version-history":[{"count":0,"href":"https:\/\/kseebsolutions.guru\/wp-json\/wp\/v2\/posts\/26857\/revisions"}],"wp:attachment":[{"href":"https:\/\/kseebsolutions.guru\/wp-json\/wp\/v2\/media?parent=26857"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/kseebsolutions.guru\/wp-json\/wp\/v2\/categories?post=26857"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/kseebsolutions.guru\/wp-json\/wp\/v2\/tags?post=26857"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}} |