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Human Eye and Colourful world Class 10 Important Questions with Answers Science Chapter 11
Human Eye and Colourful world Class 10 Important Questions Short Answer Type
Question 1.
(a) Draw a diagram to show the formation of image of a distant object by a myopic eye. How can such an eye defect be remedied?
(b) State two reasons due to which this eye defect may be caused.
(c) A person with a myopic eye cannot see objects beyond a distance of 1.5 m. What would be the power of the corrective lens used to restore proper vision? (CBSE 2008)
Answer:
(a) Object at infinity, image is formed in front of retina.
Corrected by concave lens
(b) Myopia is caused due to:
- Elongation of eye ball
- Excessive curvature in cornea, focal length decreases.
(c) Far point of myopic eye is 1.5 m = u to change far point to infinity = v
focal length of power → P = ?, f = ?
Question 2.
Why is red colour selected for danger signal lights? (CBSE 2008)
Answer:
Red colour light has maximum wavelength, it does not scatter due to atmosphere and reaches our eyes, travels fast and hence used for danger signals.
Question 3.
(a) What is meant by dispersion of white light? Describe the formation of rainbow in the sky with the help of a diagram.
(b) What is hypermetropia? Draw ray diagrams to show the image formation of an objects by
(i) hypermetropic eye
(ii) Correction made with a suitable lens for hypermetropic eye. (AI 2008)
Answer:
(a) The splitting of white light into its constituent seven colours is called dispersion of light.
Rainbow formation in the sky: The water droplets suspended in the atmosphere after rain causes the splitting of sunlight by acting as small prism. The light enters the water droplets, refracts, splits and shows internal reflection. Then again undergoes refraction to give a band of seven colours called rainbow.
(b) Hypermetropia: Also called long-sightedness. Person can see long distant objects but cannot see nearby objects distinctly. This is because the eye ball becomes smaller, focal length increases. It can be corrected by using converging lens called convex lens.
Question 4.
(a) Give reasons for the following:
(i) Colour of the clear sky is blue.
(ii) The sun can be seen about two minutes before actual sunrise.
(iii) We cannot see an object clearly if it is placed very close to the eyes.
(b) What is presbyopia? Write two causes of this defect. (AI 2008)
Answer:
(a) (i) Clear sky appears blue because the white light of sun when enters the earth’s atmosphere the large number of molecules present in the earth’s atmosphere scatter the blue colour more strongly than red light. As blue light scatters the maximum it reaches our eyes.
(ii) The sun is visible to us 2 minutes before the actual sunrise because of atmospheric refraction. When the sun is below the horizon, the light travelling from rarer to denser medium, thus it bends and reaches our eyes creating an impression that it is above the horizon.
(b) Presbyopia: The person suffering from this disease cannot see nearby as well as far off objects. It is caused due to weakening of ciliary muscles. This defect is caused due to ageing. The lens is not able to change the focal length. It can be corrected by using bi-focal lens.
Question 5.
(a) What is hypermetropia?
(b) What are the two causes of the defect of vision?
(c) How can this defect of the eye be corrected? Illustrate your answer by drawing ray diagrams to show the formation of image by
(i) a hypermetropic eye
(ii) a hypermetropic eye corrected with a suitable lens. (Foreign 2008)
(OR)
What is hypermetropia? State the two causes of hypermetropia. With the help of ray diagram show:
(i) the eye defect hypermetropia.
(ii) correction of hypermetropia by using a lens. (CBSE 2009)
Answer:
(a) Hypermetropia: It is also called long-sightedness. The person with this eye defect can see far off objects but cannot see nearby objects clearly. The image is formed beyond retina.
(b) Two causes
- Focal length of the lens increases
- Eye ball becomes smaller
(c) Correction: It can be corrected by using a convex lens. It is a converging lens which shifts the image of the object on the retina.
Question 6.
Study the diagram given below and answer the question that it follows:
(a) Which defect of vision is represented in this case? Give reason for your answer.
(b) What could be the two causes of this defect?
(c) With the help of a diagram show how this defect can be corrected by the use of a suitable lens. (CBSE 2008C)
Answer:
(a) The defect is hypermetropia, as the image of near point is formed beyond retina.
(b) Two causes
- Focal length of the lens increases
- Eye ball becomes smaller
(c) Correction: It can be corrected by using a convex lens. It is a converging lens which shifts the image of the object on the retina.
Question 7.
(a) What is myopia? State the two causes of myopia and with the help of a labelled ray diagrams show:
(i) the eye defect myopia.
(ii) correction of myopia using a lens.
(b) Why is the normal eye unable to focus on an object placed within 10 cm from the eye? (AI 2009)
Answer:
(a) Myopia or short-sightedness – Eye can see objects at short distance. Inability of the eye in viewing long distant objects. The image falls before retina.
Causes:
- Elongation of eye ball.
- Excessive curvature in cornea and focal length of lens decreases.
Correction: By using concave lens (diverging lens), which shifts the image to the retina by diverging the rays further.
Object at infinity, image is formed in front of retina.
Corrected by concave lens
Myopia is caused due to:
- Elongation of eye ball
- Excessive curvature in cornea, focal length decreases.
(b) The near point of human eye is 25 cm which cannot be changed further hence the objects within 10 cm of the eye cannot be viewed.
Question 8.
(a) What is dispersion of white light? What is the cause of such dispersion? Draw a diagram to show the dispersion of white light by a glass prism.
(b) A glass prism is able to produce a spectrum when white light passes through it but a glass slab does not produce any spectrum. Explain why? (AI 2009)
Answer:
(a) Dispersion of light: The splitting of white light into seven colours on passing through a transparent medium like glass prism is called dispersion of light.
Diagram: Dispersion of light
we get different colours because each colour of light has different bending ebility when they pass through the glass prism due to their different speed.
(b) Dispersion does not take place in glass slab as two refracting surfaces are parallel. The light does not split into its constituent colours.
Question 9.
A star sometimes appears brighter and some other times fainter. What is this effect called? State the reason for this effect. (CBSE 2012)
Answer:
This effect is called the twinkling effect. This is due to the various layers present in the atmosphere which causes the change in the refractive index and the light undergoes multiple refraction. The amount of light entering our eye keep changing and hence the star appears to be twinkling, bright sometimes and fainter other times.
Question 10.
What is the colour of the clear sky during day time? Give reason for it. (CBSE 2012)
Answer:
(i) Clear sky appears blue because the white light of sun when enters the earth’s atmosphere the large number of molecules present in the earth’s atmosphere scatter the blue colour more strongly than red light. As blue light scatters the maximum it reaches our eyes.
(ii) The sun is visible to us 2 minutes before the actual sunrise because of atmospheric refraction. When the sun is below the horizon, the light travelling from rarer to denser medium, thus it bends and reaches our eyes creating an impression that it is above the horizon.
Presbyopia: The person suffering from this disease cannot see nearby as well as far off objects. It is caused due to weakening of ciliary muscles. This defect is caused due to ageing. The lens is not able to change the focal length. It can be corrected by using bi-focal lens.
Question 11.
What is a spectrum? Why do different coloured rays deviate differently on passing through a glass prims? (CBSE 2012)
Answer:
The band of seven colour of visible light is called spectrum. The seven colour of light are VIBGYOR, i.e. violet, indigo, blue, green, yellow and orange.
The speed of light of these colours is different when they travel into denser medium from the rare medium and also bends differently showing different deviation.
Question 12.
What is meant by the term ‘power of accommodation’ of human eye? How does it help a person to see nearby as well as distant objects clearly. (CBSE 2012)
Answer:
Power of accommodation: The ability of eye to adjust its focal length and view the nearby and far away objects by forming an image on retina is called power of accommodation of human eye.
To see the nearby objects, the ciliary muscle of the eye contracts and increases thickness of eye lens. The focal length of the eye lens decreases and the image of the nearby object is formed on the retina.
To see the far away objects the ciliary muscles relax and the eye lens become thin thereby increasing the focal length of the lens and the image of the distant object is formed clearly on the retina.
Question 13.
With the help of a labelled diagram, explain why the sun appears reddish at the sunrise and the sunset. (Delhi 2015)
Answer:
The sun is near the horizon at the sunrise and also at the sunset. Light from the Sun near the horizon passes through thicker layers of air and also covers longer distance.
Most of the blue light and the shorter wavelengths of sunlight are scattered away by the particles. Light of larger wavelength reaches us giving the reddish appearance.
Question 14.
What is meant by advance sunrise and delayed sunset? Draw a labelled diagram to explain these phenomena. (Foreign 2015)
Answer:
Due to atmospheric refraction, the sun is visible to us about two minutes before the actual sunrise and about two minutes after the actual sunset.
Question 15.
What is meant by scattering of light? Use this phenomenon to explain why the clear sky appears blue or the sun appears reddish at sunrise. (AI 2015)
Answer:
Scattering: It is the phenomenon of spreading of light (diffused reflected light) caused by minute particles (dust, smoke etc.) in the atmosphere.
Clear sky appears blue because the white light of sun when enters the earth’s atmosphere the large number of molecules present in the earth’s atmosphere scatter the blue colour more strongly than red light. As blue light scatters the maximum it reaches our eyes.
The sun is visible to us 2 minutes before the actual sunrise because of atmospheric refraction. When the sun is below the horizon, the light travelling from rarer to denser medium, thus it bends and reaches our eyes creating an impression that it is above the horizon.
Presbyopia: The person suffering from this disease cannot see nearby as well as far off objects. It is caused due to weakening of ciliary muscles. This defect is caused due to ageing. The lens is not able to change the focal length. It can be corrected by using bi-focal lens.
The sun is near the horizon at the sunrise and also at the sunset. Light from the Sun near the horizon passes through thicker layers of air and also covers longer distance.
Most of the blue light and the shorter wavelengths of sunlight are scattered away by the particles. Light of larger wavelength reaches us giving the reddish appearance.
Question 16.
Why does the sun appear reddish early in the morning? Will this phenomenon be observed by an observer on the noon? Justify your answer with a reason. (Delhi 2016)
Answer:
Early in the morning, the sun is near the horizon, sunlight reaches us after travelling a longer distance through thick layers of atmosphere. Thus most of the blue light and shorter wavelengths are scattered away by the particles in the atmosphere. The light that reaches us is of longer wavelengths giving a reddish appearance.
This phenomenon will not be observed by an observer on the moon because of the absence of atmosphere on the moon.
Question 17.
Explain in brief the reason for each of the following: (Foreign 2016)
(a) Advanced sunrise
(b) Delayed sunset
(c) Twinkling of stars
Answer:
(a) Advanced sunrise: When the sun is slightly below the horizon light rays coming from the sun travel from the rarer to denser medium layers of air because of atmospheric refraction of light, light appears to come from a higher position above the horizon. Thus the sun appears earlier than actual sunrise.
(b) Delayed sunset: Same reason as similar refraction occurs at the sunset.
(c) Stars twinkle due to atmospheric refraction of light from the stars and changing density of air around the earth.
Question 18.
Name the type of mirrors used in the design of solar furnaces. Explain how high temperature is achieved by this device. (AI 2016)
Answer:
Concave Mirrors/Converging Mirrors: When a solar furnace is placed at the focus of a large concave mirror/reflector, it focuses a parallel beam of light at a point on the furnace. Consequently a high temperature is achieved at that point after some time.
Question 19.
Describe an activity to show that the colours of white light splitted by a glass prism can be recombined to get white light by another identical glass prism. Also draw ray diagram to show the recombination of the spectrum of white light. (AI 2016)
Answer:
When a glass prism is used to obtain a spectrum of sunlight, a second identical prism in an inverted position with respect to the first position will allow all the colours of spectrum to recombine. Thus a beam of white light will emerge from the other side of the second prism.
Human Eye and Colourful world Class 10 Important Questions Long Answer Type
Question 1.
(a) A student cannot see clearly a chart hanging on a wall placed at a distance 3 m from his eye. Name the defect of vision he is suffering from. Draw a ray diagram to illustrate this defect. List its two possible causes.
(b) Draw a ray diagram to show how this defect may be corrected using a lens of appropriate focal length.
(c) An eye donation camp is being organised by social workers in your locality. How and why would you help in this cause? (CBSE 2012)
Answer:
(a) Myopia is caused due to:
- Elongation of eye ball
- Excessive curvature in cornea, focal length decreases.
(b)
(c) The human eye donation camp encourages people to donate eyes: The corneal blindness can be corrected only by a cornea donor and it can help restore the eyesight of someone’s sight.
To encourage people one should educate the family members arrd-relatives and friends about the importance of eye donation and remove the myth of eye donation.
Question 2.
A student is unable to see clearly the words written on the blackboard placed at a distance of approximately 4 m from him. Name the defect of vision the boy is suffering from. Explain the method of correcting this defect. Draw ray diagram for the:
(i) defect of vision and also
(ii) for its correction (Delhi 2015)
Answer:
Myopia or short-sightedness – Eye can see objects at short distance. Inability of the eye in viewing long distant objects. The image falls before retina.
Causes:
- Elongation of eye ball.
- Excessive curvature in cornea and focal length of lens decreases.
Corrected by concave lens
Myopia is caused due to:
- Elongation of eye ball
- Excessive curvature in cornea, focal length decreases.
(ii) Correction: By using concave lens (diverging lens), which shifts the image to the retina by diverging the rays further.
Question 3.
(a) State the function of each of the following parts of the human eye :
(i) Cornea
(ii) Iris
(iii) Pupil
(iv) Retina
(b) Millions of people of the developing countries are suffering from corneal blindness. This disease can be cured by replacing the defective cornea with the cornea of a donated eye. Your school has organised a campaign in the school and its neighbourhood in order to create awareness about this fact and motivate people to donate their eyes after death. How can you along with your classmates contribute in this noble cause? State the objectives of organising such campaigns in schools. (Foreign 2015, Delhi 2016)
Answer:
(a) (i) Cornea – Refraction of the light rays falling on the eye.
(ii) Iris – To control the size of the pupil.
(iii) Pupil – To regulate and control the amount of light entering the eye.
(iv) Retina – To act as a screen to obtain the image of object and generate electrical signals which are sent to the brain via optic nerves.
(b) Ways of motivating people for the noble cause of eye donation are street play, banners, poster, door to door campaign, etc.
Objectives:
- To develop the habit of group work.
- To work for a common cause.
- To understand social issues and problems.
Question 4.
(a) Write the importance of ciliary muscles in the human eye. Name the defect of vision that arises due to gradual weakening of the ciliary muscles in old age. What type of lenses are required by the persons suffering from this defect to see the objects clearly?
(b) Akshay, sitting in the last row in his class, could not see clearly the words written on the blackboard. When the teacher noticed it, he announced if any student sitting in the front row could volunteer to exchange his seat with Akshay. Salman immediately agreed to exchange his seat with Akshay. He could now see the words written on the blackboard clearly. The teacher thought it fit to send the message to Akshay’s parents advising them to get his eyesight checked.
In the context of the above event, answer the following questions :
(i) Which defect of vision is Akshay suffering from? Which type of lens is used to correct this defect?
(ii) State the values displayed by the teacher and Salman.
(iii) In your opinion, in what way can Akshay express his gratitude towards the teacher and Salman? (AI 2015)
Answer:
(a) Ciliary muscles modify the curvature of the eye lens to enable the eye to focus objects at varying distances and help in adjusting the focal length of the eye lens.
The gradual weakening of the ciliary muscles in old age causes presbyopia. The persons suffering from this defect need to use bifocal lenses.
(b) (i) Akshay is suffering from Myopia/Near sightedness.
Concave/Diverging lens is used to correct this defect.
(ii) The values displayed by the teacher and Salman are concerned and caring respectively.
(iii) Akshay can express his gratitude by thanking the teacher and Salman.
Question 5.
(a) What is dispersion of white light? State its cause.
(b) “Rainbow is an example of dispersion of sunlight”. Justify this statement by explaining, with the help of a labelled diagram, the formation of a rainbow in the sky. List two essential conditions for observing a rainbow. (Foreign 2016)
Answer:
(a) Definition of Dispersion: Splitting of white light into seven constituent colours by a prism.
Cause of dispersion: When white light passes through a glass prism, different constituent colours bend through different angles with respect to the incident ray and hence are separated.
(b) Conditions for observing a rainbow:
- After the rainfall/at a water fountain.
- Sun is at the back of the observer.
Question 6.
What is atmospheric refraction? Use this phenomenon to explain the following natural events. (AI 2016)
(i) Twinkling of stars
(ii) Advanced sun-rise and delayed sun-set.
Draw diagrams to illustrate your answers.
Answer:
Atmospheric Refraction: Refraction of light caused by the earth’s atmosphere due to change in the refractive star indices of different layers is called atmospheric refraction.
(i) Twinkling of stars: Stars are distant point sized source of light. The path of the rays of light coming from the star goes on varying due to atmospheric refraction slightly. Thus apparent position of the stars fluctuates and the amount of star light entering the eye flickers giving the twinkling effect.
(ii) Advanced Sunrise: When the sun is slightly below the horizon, light rays coming from the sun travel from the rarer to denser layers of air. Because of atmospheric refraction of light, light appears to come from a higher position above the horizon. Thus sun appears earlier than actual sunrise.
Delayed Sunset: Same reason as similar refraction occurs at the sunset.
