CBSE Class 10 Science Past Paper PDF, 2019-2020

Chap 11 : Human Eye and The Colorful World www.cbse.online File Revision Date : 10 July 2019 CBSE Previous Years Chapterwise Questions Exam 2019-2020 CLASS : 10th...

Chap 11 : Human Eye and The Colorful World www.cbse.online File Revision Date : 10 July 2019 CBSE Previous Years Chapterwise Questions Exam 2019-2020 CLASS : 10th CHAPTER 11 SUB : Science For more subject visit www.cbse.online or whatsapp at 8905629969 Human Eye and The Colorful World 1. ONE MARK QUESTIONS For a human eye, there is a near point, 25 cm. If the distance of the object is lesser than this distance, eye cannot see object clearly. 1. Name the essential parts of human eye, 11. When you enter from a bright sunshine into a dark Ans : [CBSE 2016] room, you are not able to see clearly for sometime, (a) Retina (6) Eye lens (c) Cornea (d) Pupil (e) Iris why? Ans : [Delhi 2015] 2. Which liquid fills the space behind the cornea? In bright light, pupil had become small. Ans : [Delhi 2016] Aqueous humour is filled in the space behind the 12. On what factor the colour of the scattered light cornea. depends? Ans : [CBSE 2015] 3. Which part of the eye controls the amount of light entering the eye? The colour of the scattered light depends on the size of scattered particles. Ans : [CBSE 2016] Pupil controls the amount of light entering the eye. 13. What is Presbyopia ? Ans : [CBSE 2014] 4. What is eye lens made of ? Presbyopia is a kind of eye defect in old persons due Ans : [CBSE 2016] to ageing. It happens due to decrease in flexibility of Eye lens is made of transparent and flexible jelly like eye lens and weakening of ciliary muscles. material. 14. What is twinkling of stars due to? 5. How is the sense of vision carried from the eye to the Ans : brain? Twinkling of star is due to atmosphere refraction. Ans : [CBSE 2016] Through optical nerve, sense of vision is carried from 15. Define dispersion of white light. eye to the brain. Ans : [CBSE 2014] 6. Which liquid fills the space between eye lens and The splitting of white light into its constituents seven retina? colours is called dispersion of light. Ans : [All India 2015] 16. What kind of lens is used in the spectacles of a person Vitreous humour. suffering from myopia (near sightedness)? Ans : [CBSE 2014] 7. Why is blind spot so called? A diverging lens/concave lens is used for a person Ans : [CBSE 2015] suffering from near sightedness/ myopia. An image formed at this point is not sent to brain. 17. Name the part of the human eye that helps in changing 8. What is the number of receptors contained in the the focal length of the eye lens. retina? Ans : [All India 2013] Ans : [CBSE 2015] Ciliary muscles help in changing the focal length of Retina contains more than 125 millions receptors the eye lens. which are of two types, rods and cones. 18. Write the value of near point of distinct vision for 9. What is meant by far point? normal eye. Ans : [CBSE 2015] Ans : [CBSE 2013] The farthest point upto which an normal human eye For a normal human eye the value of near point of can see objects clearly is known as far point. distinct vision is 25 cm. 10. Why can you not see an object clearly if it is placed 19. What is the role of pupil in a human eye? very close to your eye? Ans : [CBSE 2013] Ans : [All India 2015] Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 142 Chap 11 : Human Eye and The Colorful World www.cbse.online Pupil regulates and controls the amount of light depends. Why does the sky appear dark in space? entering in the eyes. Ans : [CBSE 2016] 20. What is the range of vision for a normal human eye? Scattering of light depends on the presence of Ans : [CBSE 2013] atmosphere which contains water droplets, molecules of air, smoke and dust particles. Range of vision is 25 cm to infinity. In the space, there is no atmosphere to scatter 21. Name the two phenomena involved in the formation light. of rainbow. 30. How can change of size of eyeball be one of the reason Ans : [CBSE 2012] for: (a) Myopic (b) Hypermetropic The phenomena involved in formation of rainbow are Compare the size of eyeball with that of a normal dispersion and total internal reflection and refraction. eye in each case. How does this change of size affect 22. Name the component of white light that deviates the the position of image in each case? least and the most while passing through a prism. Ans : [All India 2016] Ans : [CBSE 2012] (a) The eye suffering from myopia, has long eye ball Red colour deviates the least and violet colour deviates than that of normal eye due to which the retina the most. is at a larger distance from the eye lens. This results in the formation of the image in front of 23. A person is advised to wear spectacles with concave the retina. lenses. What type of defect of the vision is he suffering (b) The eye suffering from hypermetropia has short from? eye ball than that of normal eye due to which the Ans : [CBSE 2012] retina is smaller distance from the eye lens. This results in the formation of the image behind the Myopia. retina. 24. Name the part responsible for the power of 31. Sushil went to an eye specialist for check up. He accommodation of the eye. prescribed him to use spectacle lens of + 0.5D power. Ans : [CBSE 2012] a. Name the defect of vision he is suffering from. Ciliary muscles help for the power accommodation of b. Find the focal length of spectacle lens. the eye. Ans : [CBSE 2015] 25. Name the condition resulting due to the eye lens a. Hypermetropia. becoming cloudy. b. Power of spectacle P = + 0.5D Ans : [CBSE 2012] f = 1 =+ 1 m P 0.5 Cataract. or f = + 2 m positive sign means it is a convex 26. Why sky appears dark to the passengers flying at high lens. altitudes? 32. State the function of pupil and ciliary muscles. Ans : [CBSE 2012] Ans : [CBSE 2015] There is no atmosphere at high altitudes. Hence no scattered light can reach to the eye. a. Pupil controls the amount of light entering the eye. 27. A person suffering from an eye defect uses lenses of b. Ciliary muscles help in accommodation of power power – 1D. Name the defect he is suffering from and of eye lens. the nature of lens used. 33. A child sitting in a classroom is not able to read Ans : [CBSE 2012] clearly the writing on the blackboard. He uses a concave lens (negative power) because he is a. Name the type of defect from which his eye is suffering from myopia. suffering. b. With the help of a ray diagram show how this 28. Which colour of white light suffers (i) least deviation defect can be remedied. and (ii) maximum deviation when a beam of white Ans : [Delhi 2015] light passes through a glass prism? Ans : [CBSE 2011] a. Myopia b. Myopia can be remedied by using concave lens. Longer wavelength light (red) suffers least deviation and shorter wavelength (violet) suffers maximum deviation when white light is passed through a prism. TWO MARKS QUESTIONS 29. Mention the factor on which scattering of light Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 143 Chap 11 : Human Eye and The Colorful World www.cbse.online If another identical prism is placed in inverted position in front of a prism then dispersed colours obtained from first prism get recombine to produce white light. 34. What is meant by persistence of vision? Ans : [All India 2014] 40. Explain why do stars twinkle and planets do not? Ans : [CBSE 2012] On removing object seen, its impression persists on the retina for 161 th second. The inability of human The light coming from star get refracted through the brain to perceive more than two images formed on the atmospheric layers. Due to this, the star appear slightly retina within interval of 161 th of a second is called higher than its actual position. Since the densities of persistence of vision. In this case, both the images atmospheric layers changes frequently and hence the merge and give a sensation of continuity. position of the star appear changes continuously stars are very distant point-sized objects. As the path of 35. List four common defects of vision that can be rays of light coming from star is continuously changes. corrected with the use of spectacles. So sometimes light enters into our eyes and some Ans : [Delhi 2013] times it faints. This is twinkling of the star. Since (i) Myopia (ii) Hypermetropia (iii) presbyopia (iv) planets are closer to us, their size is also big. Our Astigmatism. eyes receive light from different points of the planets. Hence planets do not twinkle. 36. (a) Explain how a normal human eye is able to see 41. List two causes leading to myopia of the eye. Draw distinctly the object placed at a distance as well as those placed at a nearer distance. ray diagrams to show the image formation in case of (b) What is the far point and near point of a normal defective eye and corrected eye. human eye? Ans : [CBSE 2012] Ans : [CBSE 2013] Causes of Myopia (a) Ciliary muscles change the curvature of eye lens as a. Excessive curvature of cornea per requirement of the eye. This changes the focal b. Elongation of eye ball. length of eye lens. When muscles are relaxed, lens becomes thin and distant objects are seen clearly. While seeing closer objects, muscles contract, this thickens the eye lens and focal length decreases. (b) Far point — Infinity. Near point — 25 cm from the eye. 37. What is meant by least distance of distinct vision? How does this vary between the very young and old people? Ans : [CBSE 2013] 42. (a) What is the least distance of distinct vision for Least distance of distinct vision is the minimum distance between eye and object to see it clearly. the normal eye? (b) Does the above distance increase or decrease for In young, the least distance of distinct vision is long sighted eye? Give reason for your answer lesser and for old people it is more. with diagram. 38. Define dispersion of white light and name the colours Ans : [CBSE 2012] of white light in order. (a) For a normal human eye, the least distance of Ans : [CBSE 2012] distinct vision is 25 cm. (b) Least distance of distinct vision increases for long When white light is passed through a prism, it splits sighted eye. A hypermetropic eye can see upto into its seven constituent colours. Splitting of white infinite distance, which is more than 25 cm. light into its constituent colours is called dispersion. Seven constituent colours are – violet, indigo, blue, green, yellow, orange and red. (VIBGYOR). 39. Describe an experiment to discuss the recombination of dispersed light. Ans : [CBSE 2012] Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 144 Chap 11 : Human Eye and The Colorful World www.cbse.online through a glass prism. Ans : [CBSE 2012] a. Splitting of white light into its constituent colours when passed through a prism called dispersion of light. b. Violet colour deviates the most while passing through the glass prism. 48. Why does it take sometimes to see the objects in a dim room when we enter the room from bright sunlight outside? Ans : [CBSE 2011] In bright sunlight, pupil of eye contracts to control the light. When we enter a dim room, pupil takes some 43. A person needs a lens of power –2.5 dioptres for time to expand to allow more light to see the objects correcting his vision. Name the defect of vision he clearly. is suffering from. Which lens will he be using for the correction? Also, find the focal length of lens. 49. Why does the clear sky appear blue? How would the Ans : [CBSE 2012] sky appear in the absence of earth’s atmosphere? Ans : [CBSE 2011] P =- 2.5D The person using a lens of negative focal length Scattering of light \ l1 where l is the wavelength 4 of light, i.e. least wavelength will scatter more and f = 1 = - 1 =- 0.4 m =- 40 cm vice versa. Blue colour light has shorter wavelength P 2.5 Here negative focal length means he uses a concave and hence scattered more than other colours. In space, lens. there is no atmosphere hence no scattering of light happens in the space so space appears black. 44. Name the part of the eye where image is formed by the eye lens. What is the nature of the image formed? 50. Why do we observe difference in colours of the sun How is this image sent to the brain? during sunrise, sunset and noon? Ans : [CBSE 2012] Ans : [CBSE 2011] Retina. During the sunrise or sunset, the sun is at horizon. Most Image on the retina is inverted and real. Optic nerve of the blue light and other light of shorter wavelength sends the image to the brain. are scattered most. Only the longer wavelength (red) reaches to us. That’s why sun appears red during the 45. Explain how a normal human eye is able to see sunrise or sunset. distinctly the object placed at a distance as well as At noon, the Sun appears white because it is at those placed at a nearer distance. What is the far our head and all wavelength reaches to us due to little point and near point of a normal human eye? of the blue and violet colours are scattered due to Ans : [CBSE 2012] least distance travelled by fight. To see a near object, the focal length of the eye should 51. Why do we observe the seven colours when white light be small and vice versa. The focal length of the eye passes through a glass prism? Which component of lens can be adjusted by ciliary muscles. When one see white light deviates the least? near object, ciliary muscles decreases the focal length and for distant object, ciliary muscles increases the Ans : [CBSE 2011] focal length. Far point — Infinity. Since angle of deviation for different colour is different Near point — 25 cm from the eye. hence different colour suffers different deviation. Deviation for red colour is minimum. 46. An old person is unable to see clearly nearby object as well as distant objects, (i) What defect of vision is he 52. Draw a neat diagram to show the refraction of a light suffering from? (ii) What kind of lens will be required ray through a glass prism, and label on it the angle of to see clearly the nearby as well as distant objects? incidence and angle of deviation. Give reason. Ans : [CBSE 2011] Ans : [CBSE 2012] (i) Old person is suffering from presbyopia. (ii) He cannot see near objects as well as distant objects, so he has to use bifocal lenses which consists of concave and convex lenses both. 47. What is dispersion of light? Name the (i) component of white light that deviates the least, (ii) component of white light that deviates the most, while passing PE–Incident ray +i –Angle of incidence Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 145 Chap 11 : Human Eye and The Colorful World www.cbse.online EF–Refracted ray +r –Angle of refraction Correction: Using a concave lens myopic FS–Emergent ray +e –Angle of emergence +A –Angle of prism +D –Angle of deviation 53. (a) What is ‘power of accommodation of the eye? (b) What happens to the image distance when the object being viewed is moved away from the eye? Ans : [CBSE 2011] (a) Power of accommodation of the eye means the ability to change the focal length of the eye lens to see near and distant objects. (b) Image distance remains fixed which is equal to distance between retina and eye lens. 54. (a) What is meant by least distance of distinct vision? (b) How does the thickness of the eye lens change when we shift looking from a distant tree to (b) Due to atmospheric refraction stars twinkle. The reading a book? density of atmospheric layers keep changing due to Ans : [CBSE 2011] which point sized star sometimes appear brighter (a) Least distance of distinct vision means the or dimmer with changing position. Due to this, minimum distance upto which an eye can see stars appears twinkling. clearly. 57. (a) Write the function of each of the following parts (b) To see distant object focal length of eye lens must of human eye: be more so it becomes thinner when we want to (i) Cornea (ii) Iris read a book eye lens is comparatively thicker. (iii) Crystalline lens (iv) Ciliary muscles 55. A 14 year old student is not able to see clearly the (b) Why does the sun appear reddish early in the questions written on the blackboard placed at a morning? Will this phenomenon be observed by distance of 5 m from him. an astronaut on the Moon? Give reason to justify a. Name the defect of vision he is suffering from. your answer. b. With the help of labelled ray diagrams show how Ans : [Delhi 2018, 2017] this defect can be corrected. (a) Function of Human eye: c. Name the type of lens used to correct this defect. (i) Cornea focuses light ray to enter the eye. Ans : [CBSE 2007] (ii) Iris control and regulate amount of light a. Myopia entering the eye and control the size of pupil. b. (iii) Crystalline lens is like a convex lens which converge light rays on the retina. (iv) Ciliary muscles adjust focal length of eye lens by contraction and relaxation so that sharp image can be obtained on the retina. (b) During morning and evening time, sun is at the horizon, sunlight has to travel longer distance in atmosphere. Violet and blue colours etc. of shorter wavelength scatter in the space only. The longer wavelength red colour reaches to the observer on earth and sun appears reddish. No, because there is no atmosphere on moon and c. Concave lens no scattering of light takes place there. 58. (a) With the help of a suitable diagram explain why FIVE MARKS QUESTIONS the Sun is visible to us two minutes before the actual sunrise and two minutes after the actual sunset. 56. (a) A student is unable to see clearly the worlds (b) Name the phenomenon responsible for apparent written on the blackboard placed at a distance of flattening of the Sun’s disc at sunrise and sunset. approximately 3 m from him. Name the defect of vision the boy is suffering from State the possible Ans : [CBSE 2016] causes of this defect and explain the method of (a) The duration of the day becomes approximately 4 correcting it. minutes longer due to atmospheric refraction. We (b) Why do stars twinkle? Explain. can see the sun when it is below the horizon in the Ans : [Delhi 2018] morning. The rays of light from the sun below the horizon(s) reach to our eyes due to refraction of (a) Defects of vision: Myopia or short sightedness. light 2 minutes before it actually rises. Similarly Reasons: Excessive curvature of eye lens and the sun can be seen about 2 minutes after it elongation of eye ball. Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 146 Chap 11 : Human Eye and The Colorful World www.cbse.online actually set. Thus the duration of day time interacts with particle of matter. When sunlight increases by 4 minutes (2 minutes each time at strikes molecules in atmosphere, the light is the time sunrise or sunset). redirected in many direction. b. Scattering of blue colour is most due to shorter wavelength, where as scattering of red colour is least. All colours scattered in the sky and red colour light reaches to earth, due to this sun appears reddish. 59. Study the diagram and answer the questions the 62. With the help of scattering of light, explain the reason follows : for the difference in colours of the Sun as it appears Ans : during sunrise/sunset and noon. Ans : [CBSE 2015] At the time of sunrise or sunset it appears red where as at noon it appear white when it is overhead because at sunrise or sunset blue colour and other shorter wavelength light get scattered away while passing through the atmosphere. Scattering of longer a. Identify the defect of vision represented by this wavelength is least which reach to the earth. Due to diagram. this sun appears red during morning and evening time. b. List the two possible causes of this defect. When sun is overhead at noon, sun rays travels c. With the help of ray diagram explain how this smaller distance, due to little scattering of blue and defect can be corrected. violet colour wavelength almost all wavelengths reach Ans : [Delhi 2016] to earth and due to this sun appears white. a. The defect of vision is hypermetropia. 63. State the cause of dispersion, when white light enters b. (i) increase in focal length of eye lens a glass prism. Explain with a diagram. (ii) shortening of eye ball. Ans : [All India 2014] c. Hypermetropia can be corrected by using convex lens. When white light passes through a prism it splits into its constituent colours, because each coloured light has different speed in prism. Prism has different refractive index for these light rays and so deviates through different angles when emerge out from the prism. Deviation for violet colour (shortest wavelength) is most and for red colour (largest wavelength) deviation is least. 60. A person can see distant signboards clearly but cannot read clearly a book which is at 25 cm from his eye. Giving reason identify the defect. Draw a labelled ray 64. (a) Calculate maximum power of accommodation of a diagram to illustrate this defect and its correction. person having normal vision. Ans : [CBSE 2016] (b) A person needs to use glasses for reading Eyes defect is hypermetropia. Its causes are due to newspaper. Identify the defect in her vision and a. shortening the eye ball the type of lens she would need to correct it. b. increase in focal length of eye lens. (c) Sometimes when we enter into a dark room from bright sunlight we are unable to see objects clearly. Why? Ans : [CBSE 2014] (a) Least distance of distinct vision for a normal eye D = 25 cm. 61. What is meant by scattering of light? Use this P = 1 = 100 = 4D phenomenon to explain why the clear sky appears f 25 blue or the sun appears reddish at sunrise. For a person having normal vision, the power of accommodation is 4 D. Ans : [CBSE 2015] (b) Hypermetropia, to correct hypermetropia convex a. Scattering of light is phenomenon by which beam lens is needed. of light is spreaded in many direction when it Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 147 Chap 11 : Human Eye and The Colorful World www.cbse.online (c) In bright light the pupil contract its size becomes small to control the light, but when we enter into a dark room it take sometime for the pupil to expand to allow more light in dark room. 65. State one function each of iris, pupil, and cornea. It can be corrected with the help of a convex lens Ans : [CBSE 2014] as shown. a. Iris: It controls the amount of light entering the eye by changing the size of pupil. b. Pupil: Pupil is a part of the eye through which light enters in the eye. c. Cornea: It is a thin membrane which covers the eye ball. Light enters the eye through cornea 69. A person is unable to read a book clearly when kept where it is refracted most. at a distance of 25 cm from his eye. Name the defect. How can it be corrected? Draw ray diagrams for (i) 66. (a) Explain the phenomenon of scattering of light. defective eye (ii) corrected eye and explain them. State the factor on which colour of scattered light depends. Ans : [CBSE 2013] (b) List any two natural phenomenon based on The person cannot read a book at a distance of 25 cm scattering of light. from his eyes. So he is suffering from long sightedness/ Ans : [CBSE 2014] hypermetropia. It can be corrected by using convex lens of suitable focal length. (a) Scattering of light is the phenomenon due to which light gets deflected by the atoms or molecules of different atmospheric gases and suspended particles present in atmosphere. Scattering depends upon size of the particles of the medium through which light passes. (b) Two natural phenomenon based on scattering are (i) Reddish colour of sky during sunrise and sunset, (ii) Blue colour of sky. 67. A person cannot see objects farther than 12 m from the eye clearly. Name the defect of vision he is suffering from and the lens that should be used for correction of this defect. Illustrate with the help of a diagram, how this lens will correct the defective vision? Ans : [CBSE 2011, 2013] He is myopic. Myopia can be corrected by using concave lens. 70. With the help of a diagram, explain the formation of a rainbow in the sky. Ans : [CBSE 2012] The water droplets in the atmosphere act like small prisms. These droplets refract and disperse the incident sunlight, then reflect it internally and finally refract it again when it comes out of the rain drop. Due to distortion of sunlight and internally reflection, different colours reach to the observer. 68. A person cannot read a book at distances less than 50 cm. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagrams to show the image formation: a. by defective eye and b. after using corrective lens. Ans : [CBSE 2011, 2013] a. Either the hypermetropic eyeball is too short or b. The ciliary muscle is unable to change the shape of the lens enough to properly focus the image i.e., the focal length of the eye lens is too long. This 71. (a) What is meant by dispersion of white light? Draw defect is called hypermetropia. a diagram to show the dispersion of white light by Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 148 Chap 11 : Human Eye and The Colorful World www.cbse.online a glass prism. e. Due to absence of atmosphere in the space, there (b) Light of two colours A and B pass through a is no scattering and hence space appears black/ prism. A deviates more than B from its path of dark. incidence. Which colour has a higher speed in the prism? 74. (a) If a person wears lens of power - 6D for distant vision and for correcting his near vision he needs Ans : [CBSE 2011] a lens of +2D. Determine the focal length of the (a) Splitting of white light into its constituent colours lenses in both the case. when it is passed through a prism is called (b) Give reason for the following natural phenomenon: dispersion of white light. (i) Stars twinkle (ii) Planets do not twinkle (iii) Stars appear raised in the sky. Ans : [CBSE 2016] (a) (i) P1 = - 6D as f1 = 1 =- 1 m P1 6 f1 = - 100 cm =- 16.66 cm 6 (ii) P2 = + 2D as f2 = 1 =+ 1 m P2 2 (b) B f2 = 50 cm (b) (i) Due to continuous changes in the densities of the atmospheric layers the apparent position FIVE MARKS QUESTIONS of the star also changes; which make the light coming from the distant point sized star brighter and dimmer. The light coming 72. (a) A student is unable to see clearly the words from the stars therefore gives a shaking written on the black board placed at a distance of appearances, which gives the impression of approximately 3 m from him. Name the defect of twinkling of a star. vision the boy is suffering from. State the possible (ii) Since the planets are closer to us. Due to this causes of this defect and explain the method of they appear a combination of large point-sizes correcting it. source of light, and change in the path of light (b) Why do stars twinkle? Explain. coming from the planets is not significant. So Ans : [CBSE 2017] planets do not appear twinkling. (a) He is suffering from myopia. (iii) Due to atmospheric refraction, a star appears Causes of myopia: to be slightly higher than its actual position (i) elongation of eye ball. in sky. (ii) excessive curvature of cornea. Concave lens of suitable power is used to correct 75. (a) State the reasons which lead to hypermetropia. myopia. With the help of suitable diagram, explain this (b) Light coming from stars when enter in the Earth’s defect of vision and its correction. atmosphere suffers refraction from the atmospheric (b) Draw diagram of an experimental arrangement for layers. Since the densities of atmospheric gases observing scattering of light in colloidal solution. changes frequently. Since the stars are point sized Name the two chemicals used in this activity. and at a far distance so sometimes star appear Ans : [All India 2015] brighter and sometimes dimmer which gives the a. In hypermetropia a person cannot see near by impression as the stars twinkling. objects clearly. Its is due to shortening of the eye ball or due to increase in focal length of eye lens. 73. Account for the following: To correct hypermetropia, a convex lens of suitable a. Part of the human eye that helps in changing the focal length is needed. focal length of the eye lens. b. b. The condition resulting due to the eye lens becoming cloudy. c. The factors on which colour of the scattered white light depends. d. The range of vision of a normal eye. e. The sky appears dark to the astronauts in the space. Ans : [CBSE 2016] a. Ciliary muscles. 76. What is meant by scattering of light? Mention the b. Cataract. factor on which it depends. Explain why the colour of c. Size of the suspended particles in the medium the clear sky is blue? An Astronaut in space finds sky through which white, light passes. to be dark. Explain reason for this observation. d. 25 cm to infinity is the range of vision of normal Ans : [CBSE2015] eye. (a) Scattering of light is the phenomenon due to Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 149 Chap 11 : Human Eye and The Colorful World www.cbse.online which light gets deflected by the atoms, molecules prism. Collect these coloured lights on a screen or or particles of the medium when light falls on white sheet of paper. This prove that white light them. These are known as scatterer particles. is made up of seven colours. (b) Factors on which scattering depends are the size (b) Violet colour deviates most whereas red colour of the atoms, molecules of the scatterer. deviates least because they have different speeds (c) When sunlight falls on the atoms or molecules of in prism they have different refractive indices and the gases shorter wavelengths J like of blue colour hence have different angle of deviation. get scattered more due to which sky appears blue. In space there is no atmosphere, so there is 80. (a) Explain why colour of clear sky appears blue no scattering hence the sky appears dark/black. during the day with the help of diagram. (b) Explain why Sun looks reddish at the time of 77. (a) How does refraction take place in the atmosphere? sunrise and sunset. Why do stars twinkle but not the planets? Ans : [CBSE 2014] (b) State any two effects of atmospheric refraction on (a) Due to scattering of blue colours by the dust the sun as observed from the earth. particles present in the atmosphere. Ans : [C8SE2015] (b) During the Sunrise or Sunset, Sun is at the (a) Due to change in the density of atmospheric layers horizon, and sunlight travels a longer distance when light travel through them gets refracted. It in the atmosphere. Due to this all colours get is known as atmospheric refraction. Due to this scattered except red which reaches to the eye of atmospheric refraction intensity of light, coming the observer to whom sun appears reddish in the from a point sized star same times becomes more morning or evening. and sometimes less, which gives the appearance of twinkling of the star. (b) (i) Sun can be seen two minute prior it rises and two minute before it sets. (ii) Twinkling of star. 78. Draw a neat labelled diagram of the structure of the human eye and mention the functions of any four parts. Ans : [CBSE 2015] 81. A person cannot see the objects distinctly, when placed beyond 2 m. a. Identify the eye defect. b. Give two reasons for this defect. c. Calculate the power and nature of the lens he should be using to see the distant objects clearly. d. Draw the ray diagrams for the defective and the corrected eye. Ans : [CBSE 2011, 2013] a. Myopia. b. Elongation of eye ball or excessive curvature of a. Cornea: A thin membrane which covers the eye cornea. ball which allows the light to enter and refracts c. P = 1 = 1 =- 0.5D the light to focus it as the crystalline lens. f -2 b. Eye Lens: It is a convex lens made of transparent He will be advised to used a concave lens of power and flexible jelly like material. Its curvature is – 0.5 D. adjusted by ciliary muscles. d. c. Iris: It controls and regulates the light entering the eye by changing the size of pupil. d. Pupil: It is a hole in the middle of the iris through which light enters the eye. 79. (a) Demonstrate an activity with a well labelled diagram to prove that white light is made up of seven colours. (b) Which colour of light bends least and which one the most while passing out from the prism. Also state the reason for the same. Ans : [CBSE 2014] 82. A person cannot see the objects distinctly, when (a) To demonstrate that white light is made up of placed at a distance less than 50 cm. seven colours, take a prism. Allow white light to a. Identify the defect of vision. fall on its one focus through a pin hole. Rotate the b. Give two reasons for this defect. prism until the coloured light emerge out from the c. Calculate the power and nature of the lens he Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 150 Chap 11 : Human Eye and The Colorful World www.cbse.online should be using to see clearly the object placed at a distance of 25 cm from his eyes. d. Draw the ray diagrams for the defective and the corrected eye. Ans : [CBSE 2011] a. Hypermetropia. b. Decrease in power of eye lens or shortening of eye ball. 84. (a) Explain the following terms used in relation to defects of vision and corrections provided for c. u =- 25 cm, v = - 50 cm them: 1 = 1 - 1 =- 1 + 1 (i) Myopia f v u 50 25 (ii) Astigmatism = - 1 + 2 = + 1 cm-1 (iii) Bifocal lenses 50 50 (iv) Far sightedness. (b) Describe with a ray diagram how a person with P = 1 = 100 + 2D f 50 myopia can be helped by spectacles. d. Ans : [CBSE 2006] (a) (i) Myopia is a kind of defect in human eye due to which a person can see near by objects clearly but unable to see the distant objects. Myopia is due to (i) excessive curvature of cornea (ii) elongation of eye ball. (ii) Astigmatism is a kind of human eye defect in which he cannot see simultaneously horizontal and vertical lines both. This defect arises either when the cornea or the eye lens or both are not perfectly spherical. It can be corrected by using cylindrical lenses. (iii) Bifocal lenses with the ageing a person may suffer myopia and hypermetropia. For 83. (a) What is dispersion of white light? What is the correction of these defects he is advised to cause of such dispersion? Draw a diagram, to show use bifocal lenses whose upper half is concave the dispersion of white light by a glass prism. and lower part is convex to see distant and (b) A glass prism is able to produce a spectrum when reading purposes respectively. white light passes through it but a glass slab does (iv) Far sightedness, a person suffering from this not produce any spectrum. Explain why it is so. defect can see distant objects but unable to Ans : [CBSE 2009] see nearby objects clearly. The image of an objects is formed beyond the retina. Such (a) Dispersion : When white light is passed through a defects can be corrected by using a convex prism it splits into its constituent colours splitting lens. of white light into its constituent colours is known (b) A person with myopic eye may be advice to use a as dispersion. concave lens of suitable power/ focal length. Light of all wavelengths in vacuum travel with the same speed but have the different speeds in a medium due to different refractive light of indices for them. As a result different wavelength, deviate at different angle. Red colour deviates least when as violet colour deviates most. (b) In glass slab also, dispersion takes place at AB surface, but these splitted colours emerge out in the form of a parallel beam which becomes white. A glass slab whose focus are parallel can be considered as comprising two prisms of same refractive angle. The second identical prism can be considered in an inverted position w.r.t. first prism. When a beam of white light passes from one prism it get dispersed, but on passing through the second inverted prism, the spectrum recombine to form a white light. 85. (a) State two main causes of a person developing near sightedness. With the 3 help of a ray diagram, suggest how he can be helped to overcome this Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 151 Chap 11 : Human Eye and The Colorful World www.cbse.online disability? the lens he should use. (b) The far point of a myopic person is 150 cm in Ans : [All India 2015] front of the eye. Calculate the focal length and The person should wear a concave lens. For myopic power of a lens required to enable him to see eye u = 3, v =- 40 distant objects clearly. Ans : [CBSE 2004] 1 =1-1 f v u a. Elongation of eye ball, and excessive curvature of 1 = 1 - 1 cornea. He may be adviced.to use a concave lens f - 40 3 of suitable focal–length. 1 =- 1 f 40 P = 100 =- 100 =- 2.5D f ^cmh 40 89. The far point of a myopic person is 150 cm in front of the eye. Calculate the focal length and the power of a lens required to enable him to see distant objects clearly. Ans : [CBSE 2014] For myopic person b. f =- 150 cm u = 3, v = - 150 cm f =? P = 1 = 100 =- 0.66 D f - 150 From lens formula 1 = 1 - 1 f v u 86. A person with a defective eye-vision is unable to see = 1 - 1 =- 1 the objects nearer than 1.5 m. He wants to read books - 150 3 150 at a distance of 30 cm. Find the nature, focal length and power of the lens he needs in his spectacles. P = 100 =- 100 =- 0.66 D f ^cmh 150 Ans : [CBSE 2016] =- 0.66 D Defect is hypermetropia v =- 1.5 m or - 150 cm, u =- 30 cm 90. A person needs a lens of power –0.5 dioptre for 1-1 = 1 correcting his distant vision he needs a lens of power v u f +1.5 dioptre for correcting his near vision. What is the focal length of the lens required for correcting his 1 = 1 - 1 f - 150 - 30 (i) distant vision, (ii) near vision? Ans : [CBSE 2011] =- 1 + 1 = - 1 + 5 i. For correcting his distant vision. 150 30 150 P = - 0.5 D f =+ 150 =+ 37.5 cm 4 f = 1 = 1 =- 2.0 m A convex lens of focal length 37.5 cm is required P - 0.5 ii. For correcting his near vision Power = 100 = 100 =+ 2.67 D f ^cmh 37.5 f = 1 = 1 =+ 0.67 m P + 1.5 87. The far point of a myopic person is 80 cm in front of WWW.CBSE.ONLINE the eyes. What is the nature and power of the lens required to enable him to see very distant objects NO NEED TO PURCHASE ANY BOOKS distinctly? For session 2019-2020 free pdf will be available at Ans : [CBSE 2016] www.cbse.online for 1. Previous 15 Years Exams Chapter-wise Question Concave lens is used for myopic eye for point x = 80 Bank cm. 2. Previous Ten Years Exam Paper (Paper-wise). For viewing fat distant object, focal length of lens. 3. 20 Model Paper (All Solved). f =- x =- 80 cm 4. NCERT Solutions P = 100 = 100 D All material will be solved and free pdf. It will be f ^cmh - 80 provided by 30 September and will be updated regularly. Disclaimer : www.cbse.online is not affiliated to Central Board of Secondary Education, =- 1.25 D New Delhi in any manner. www.cbse.online is a private organization which provide free study material pdfs to students. At www.cbse.online CBSE stands for Canny Books For School Education 88. Far point of a myopic person is 40 cm. What type of lens, should he wear so as to see the distant objects clearly? Calculate the focal length and the power of Download all GUIDE and Sample Paper pdfs from www.cbse.online or www.rava.org.in Page 152