CBSE Class 10 Science HOTs Question Human Eye and Colourful World

Question. Twinkling of stars is due to
(a) reflection of light by clouds
(b) scattering of light by dust particles
(c) dispersion of light by water drops
(d) atmospheric refraction of starlight

Answer : D

Question. The deflection of light by minute particles and molecules of the atmosphere in all direction is called ____________ of light.
(a) dispersion
(b) scattering
(c) interference
(d) tyndell effect

Answer : B

Question. The black opening between the aqueous humour and the lens is called
(a) retina
(b) iris
(c) cornea
(d) pupil

Answer : D

Question. Which of the following is a natural phenomenon which is caused by the dispersion of sunlight in the sky?
(a) Twinkling of stars
(b) Stars seem higher than they actually are
(c) Advanced sunrise and delayed sunset
(d) Rainbow

Answer : D

Question. Myopia and hypermetropia can be corrected by
(a) Concave and plano-convex lens
(b) Concave and convex lens
(c) Convex and concave lens
(d) Plano-concave lens for both defects.

Answer : B

Question. The danger signals installed at the top of tall buildings are red in colour. These can be easily seen from a distance because among all other colours, the red light
(a) is scattered the most by smoke or fog
(b) is scattered the least by smoke or fog
(b) is absorbed the most by smoke or fog
(c) moves fastest in air

Answer : B

Question. The splitting of white light into different colours on passing through a prism is called
(a) reflection
(b) refraction
(c) dispersion
(d) deviation

Answer : C

Question. Bi-focal lens are required to correct
(a) astigmatism
(b) coma
(c) myopia
(d) presbyopia

Answer : D

Question. The human eye can focus objects at different distances by adjusting the focal length of the eye lens. This is due to
(a) presbyopia
(b) accommodation
(c) near-sightedness
(d) farsightedness.
Answer : B

Question. The least distance of distinct vision for a young adult with normal vision is about
(a) 25 m
(b) 2.5 cm
(c) 25 cm
(d) 2.5 m
Answer : C

Question. The human eye forms the image of an object at its
(a) cornea
(b) iris
(c) pupil
(d) retina
Answer : D

Question. The change in focal length of an eye lens is caused by the action of the
(a) pupil
(b) retina
(c) ciliary muscles
(d) iris
Answer : C

Question. When white light enters a glass prism from air, the angle of deviation is maximum for
(a) blue light
(b) yellow light
(c) red light
(d) violet light

Answer : C

Question. The image formed on the retina of the human eye is
(a) virtual and inverted
(b) real and inverted
(c) real and erect
(d) virtual and erect

Answer : B

Question. When white light enters a prism, it gets split into its constituent colours. This is due to
(a) different refractive index for different wavelength of each colour
(b) each colours has same velocity in the prism.
(c) prism material have high density.
(d) Scattering of light

Answer : A

Question. The air layer of atmosphere whose temperature is less then the hot layer behave as optically
(a) denser medium
(b) rarer medium
(c) inactive medium
(d) either denser or rarer medium

Answer : A

Question. Refraction of light by the earth’s atmosphere due to variation in air density is called
(a) atmospheric reflection
(b) atmospheric dispersion
(c) atmospheric scattering
(d) atmospheric refraction

Answer : D

Question. At noon, the Sun appears white as
(a) blue colour is scattered the most
(b) red colour is scattered the most
(c) light is least scattered
(d) all the colours of the white light are scattered away

Answer : C

Question. One cannot see through the fog, because
(a) refractive index of the fog is very high
(b) light suffers total reflection at droplets
(c) fog absorbs light
(d) light is scattered by the droplets

Answer : D

Question. The medical condition in which the lens of the eye of a person becomes progressively cloudy resulting in blurred vision is called
(a) myopia
(b) hypermetropia
(c) presbyopia
(d) cataract

Answer : D

Question. Near and far points of a young person normal eye respectively are
(a) 0 and infinity
(b) 0 and 25 cm
(c) 25 cm and infinity
(d) 25 cm and 150 cm.

Answer : C

Question. A person cannot see distinctly objects kept beyond 2 m. This defect can be corrected by using a lens of power [NCERT Exemplar Problems]
(a) + 0.5 D
(b) – 0.5 D
(c) + 0.2 D
(d) – 0.2 D

Answer : B

Question. Name the scientist who was the first to use a glass prism to obtain the spectrum of sunlight.
(a) Isaac Newton
(b) Einstein
(c) Kepler
(d) Hans Christian Oersted

Answer : A

Question. A prism ABC (with BC as base) is placed in different orientations. A narrow beam of white light is incident on the prism as shown in figure. In which of the following cases, after dispersion, the third colour from the top corresponds to the colour of the sky? 

Answer : B

True and False :

Question. A lens of higher focal length has less power. 
Answer: True

Question. Power of accommodation for a normal eye is 4 dioptre.
Answer: True

Question. The optical nerves carry signals to the brain. 
Answer: True

Question. 28 frames are projected per second in motion picture. 
Answer: False

Question. Myopia is caused due to excessive curvature in cornea. 
Answer: True

Fill in the Blanks :

Question. Most of the refraction of light rays entering the eye occurs at the outer surface of the ……….. .
Answer: cornea

Question. Red light is used for signals as it is ____________ scattered.
Answer: less

Question. ……….. of light causes the blue colour of sky and reddening of the Sun at sunrise and sunset.
Answer: Scattering

Question. When light falls at critical angle on the surface of a rarer medium while coming from a denser medium, the refracting angle is ____________ .
Answer: 90°

Question. Bi-focal lens is used to correct ____________ refractive error.
Answer: presbyopic

Important Questions for NCERT Class 10 Science Human Eye and Colourful World
 

Very Short Answer type Questions :

Question. In which direction, the near point of hypermetropic eye is shifted from the normal near point?
Answer: The near point of hypermetropic eye is shifted farther away from the normal near point.

Question. What is the nature of eye lens of human eye and that of the image formed at the retina of the eye by it?
Answer: The nature of eye lens in human eye is convex nature of the image formed on the retina by it is real, inverted and diminished.

Question. Mention the role of optic nerve in the human eye.
Answer: Role of optic nerve in human eye: It transmits the visual information in the form of electrical signal generated at retina to the brain.

Question. What is the other name of old hypermetropia?
Answer: Presbyopia.

Question. Name the part of our eyes that helps us to focus near and distant objects in quick succession.
Answer: Ciliary muscles help in changing the focal length of the eye lens.

Question. A person suffering from an eye defect uses lenses of power ID. Name the defect he is suffering from and the nature of lens used.
Answer: Hypermetropia; convex lens.

Question. Name the part responsible for the power of accommodation of the human eye.
Or
Name the component of eye that is responsible for the adjustment of eye lens? 
Answer: Explanation: Ciliary muscles

Question. In a human eye, name the following parts:
(a) a thin membrane which allows light to enter the eye.
(b) the muscles which help in changing the focal length of eye lens.
Answer: (a) Cornea
(b) Ciliary muscles

Please refer to link below for CBSE Class 10 Biology HOTs-Human Eye and Colourful world.

Human Eye and Colourful World

Very Short Answer Type Questions

Question. What is the function of optic nerve in human eye ?
Answer : Optic nerve carries the image formed on the retina to the brain in the form of electrical signals.

Question. What is range of vision ?
Answer : Range of vision of a normal human eye is between it’s near point and far point i.e,from 25cm to infinity.

Question. Why do different colours deviate through different angles on passing through a prism?
Answer : This is because different colours travel through glass with different speeds and glass has different refractive index for different colours.

Question. As light rays pass from air into glass prism, are they refracted towards or away from the normal ?
Answer : Towards the normal.

Question. Which color has largest wavelength ?
Answer : Red color.

Question. Which defect of vision can be rectified using a concave lens ?
Answer : Myopia.

Question. What phenomenon causes twinkling of star on a clear night ?
Answer :  Atmospheric refraction.

Question. What is meant by scattering of light ?
Answer : Change of direction of light on striking a scatterer.

Question. Why does the sky appear black instead of blue to an astronaut?
Answer : The upper atmosphere does not have particle or dust etc. as a result there is no scattering of light and hence the sky appear dark in stead of blue to an astronaut.

Question. What is the basic cause of atmospheric refraction?
Answer : The basic cause of refraction is variation in optical density of different layers of earth’s atmosphere. The sun passes through earth’s atmos

Question. Why does clear sky look blue?
Answer : Because blue color having smallest wavelength is scattered most, Amount of scattering is directly proportional to 1/λ⁴

Question. Can visible light be scattered by atoms/molecules in earth’s atmosphere?
Answer : Yes, as size of molecules/atoms is much less then wavelength of light.

Question. What is a spectrum?
Answer : The band of seven colours obtained by dispersion of white light is called spectrum.

Question. Name the defect of vision in person
    a. Whose near point is more than 25cm away?.
    b. Whose far point is less than infinity.
Answer :
a. Hypermetropia
b. Myopia

Short Answer Type Questions

7. Why is a normal eye not able to see clearly the objects placed closer than 25 cm?
Answer : A normal eye is unable to clearly see the objects placed closer than 25 cm because the ciliary muscles of eyes are unable to contract beyond a certain limit. If the object is placed at a distance less than 25 cm from the eye, then the object appears blurred and produces strain in the eyes.

Question. What happens to the image distance in the eye when we increase the distanceof an object from the eye?
Answer :  Since the size of eyes cannot increase or decrease, the image distance remains constant. When we increase the distance of an object from the eye, the image distance in the eye does not change. The increase in the object distance is compensated by the change in the focal length of the eye lens. The focal length of the eyes changes in such a way that the image is always formed at the retina of the eye.

Question. When a monochromatic light having only one wavelength, passes through a prism, will it show dispersion?
Answer: No, it will not show dispersion. It will only show deviation.

Question. What is colour-blindness? What kind of retinal cells are lacking in person suffering from this defect?
Answer : The defect of the eye due to which a person is unable to distinguish between certain colours, is known as colour blindness. Cone-shaped retinal cells are responsible for making a person differentiate between colours. The colour blind persons do not possess cone cells that respond to certain colours.

Question. How does eye control the amount of light entering it?
Answer : The amount of light entering the eye is controlled by the pupil and further the size of the pupil is controlled by iris.

Question. Name the component of white light that deviates the least and the component that deviates the most while passing through a glass prism.
Answer : Least deviated component: Red
Most deviated component: Violet

Question. Why do birds fly back to their nest in the evening?
Answer : Birds lack light sensitive cells called rods, due to lack of these cells they cannot see the objects clearly in less/dim light.

Question. Why do you take time to see objects when you enter a dim lighted room from outside in the sun?
Answer : In the sun light the size of pupil, is small but when one enters the dim light, it takes some time for iris to adjust the size of pupil and the light sensitive cells take some time to get activated.

Question. When white light enters the prism, which colour of light deviates/bends the least and which colour bends the most?
Answer : The light that bends the least is red colour and the light that bends the maximum is violet colour light.

Question. Why does a ray of light splits into different colours on passing through a glass prism?
Answer : When light rays enter the glass prism the angle at which it bends makes the light split into its seven components because the speed of each component of light is different and due to the bending every component shows its different ability to pass through it.

Question. The sun appears to be red at the time of sunset and sunrise. Give the reason.
Answer : Sun appears red during sunset or sunrise because at this time the sun is far from the earth and the light that reaches the earth from the sun scatters the most and all other colours of light gets scattered. The least scattered light is red and it enters our eye.

Question. Why doesn’t planets appear to be twinkling?
Answer : Planets are big enough and quite closer to the earth, due to these two properties the
planets do not appear to be twinkling.

Question. What is internal reflection?
Answer : When a light rays enters from one medium to another (e.g., rarer to denser i.e., air to water droplet) then a ray of light instead of passing through it reflects in the second medium then it is said to be internal reflection of light.

Question. Why can’t we see object very close to our eye?
Answer : The objects are seen only when the image forms on retina when the light rays pass through the lens. The lens has its fixed ability of changing the focal length with the help of ciliary muscles.
Ciliary muscles cannot be contracted beyond a certain limit to change the focal length of eye lens. The objects kept very close to our eye cannot be focused by ciliary muscles.

Question. What is myopia? How can it be corrected? 
Answer : Myopia is an eye defect also called short-sightedness. In this type of defect person can see nearby objects clearly but cannot see far off objects clearly. It may be caused due to the increase in the size of eye ball or due to the decrease in the focal length of the eye lens.
Correction–It can be corrected by using concave lens of appropriate focal length.

More Questions for Practice

1. A person can see only objects beyond 1m. From his eyes. Name the defect of the eye.

2. Out of light of blue and red colours which one is scattered most?

3. What is the function of crystalline lens in the human eye?

4. Which phenomenon is responsible for increasing the apparent length of the day by 4 minute?

5. What is the far point of a person suffering from Myopia.

6. What name is given to front transparent part of human eye?

7. Where do we see :(1) Concave and (2) Convex lens in bifocal lenses.

8. What is the nature of image formed by our eye?

9. Name the liquid which is present between eye lens and cornea.

10. Where does most of the refraction of light in an eye occurs?

11. Which kind of lens is an eye lens?

12. What is the cause of dispersion of light?

13. Under very dim light, we are able to see the objects but can not distinguish between colours why ?

14. What is the range of vision for normal human eye ?

15. How is the amount of light entering the eye controlled ?

16. What is the colour of danger signal? Why?

17. What is rainbow? How is rainbow formed?

18. State two causes of myopic vision.

19. How an uncorrected myopic eye sees far off objects.

20. What is presbyopia? Name the type of lens which can be used to correct presbyopia.

21. Explain why planet do not twinkle at night?

22. Explain about the colour of the sun at sunrise and sunset.

23. Define the term (1) Near point (2) Far point

24. Why is a normal eye not able to see clearly the object closer than 25 cm.

25. Draw a ray diagram to show the refraction of light through a glass prism on the diagram mark.

(a) Incident ray (b) Emergent ray and (c) Angle of deviation

26. How is the dispersed white light recomposed ?

27 The near point of a hypermetropic eye is at 75 cm from the eye. What is the power of the lens required to enable him to read clearly a book held at 25 cm from the eye.

Very Short Answer Type Questions

Question. What is the least distance of distinct vision of a normal human eye ?
Answer : 25cm.

Question. Name the muscle responsible for bringing change in the focal length of the eye lens ?
Answer : Ciliary muscle.

Question. Name one defect of vision which cannot be corrected by any type of spectacle lenses ?
Answer : Cataract.

Question. State one effect produced by the scattering of light by the atmosphere ?
Answer : Tyndall effect.

Question. What is the nature of image formed on the retina of the eye ?
Answer : Real and inverted.

Question. What type of lens is used for correcting hypermetropia ?
Answer : Convex lens.

Question. Who was the first person to obtain the spectrum of sunlight ?
Answer : Sir Isaac Newton.

Short Answer Type Questions

Question. The image formed on retina is inverted but we see the object erect. Why?
Answer : The image formed on retina is inverted, this image is formed on the light sensitive cells called rods and cones of the retina which generates electrical signals. This signal reaches brain via optic nerve. It is the brain that interprets this image and while processing the image it helps in perceiving objects as they are.

Question. Why danger signals are red?
Answer : Danger signals are of red colour, as it scatters the least and can be seen from the maximum distance.

Question. Why are two eyes more helpful for us to see as compared to one?
Answer : Two eyes are more helpful as one eye gives only a view of 150° angle where as two eyes increase the view by making it wide to 180° angle. Two eyes also helps us to see the objects in dim light or darkness clearly. Two eyes give stereoscopic vision helping us assess the depth of vision.

Question. Explain the phenomenon which causes twinkling of stars.
Answer : The phenomenon is atmospheric refraction. In this case the star are point source illuminated objects which are very far from us when light travels through atmosphere it bends, and due to this the amount of light entering the eye is different each time which gives the twinkling effect.

Question. In dispersion of white light through prism, which colour deviates most and which colour the least? Why do they deviate differently?
Answer : The colour of light that deviates least is red and violet deviates the maximum. The difference in deviation is due to the difference in wavelength and speed of each colour of light, also due to different bending ability when it passes through the prism.

Question. Give reason for early sunrise and delayed sunset.
Answer : 

Sun being far off the light rays entering our eye gets refracted several times due to the atmosphere and the sunrise and sunset are seen to us due to the bending of light and that light enters our eye to visualise the sun at that particular point.

Question. What is the direction of rainbow formation? What is the position of red colour in rainbow?
Answer : Rainbow is always formed in the direction opposite to sun. The position of red colour in the rainbow is at the top.

Question. A short-sighted person cannot see clearly beyond 5 cm. Calculate the power of lens required to correct his vision to normal?
Answer :  f = – 5 cm
P = 1/f = −1/5
= 0.20
∴ Power = 0.2 Dioptre

Question. What is night blindness and colour blindness?
Answer : When a person lacks rod cells in retina he is not able to see the objects clearly in less/dim light, such a defect is called night blindness.
When a person lacks cone cells in retina he is not able to see/distinguish between different colours, such a defect of eye is called as colour blindness.

Question. What is hypermetropia? How can it be corrected?
Answer : Hypermetropia is an eye defect also called as long-sightedness. Person can see a far off objects but cannot see nearby objects. It is because the image is formed beyond retina.
Cause – (a) The focal length of the eye lens is too long.
(b) The eyeball has become too small.
Correction: It can be corrected by using convex lens of appropriate power.

Long Answer Questions

Question. Describe with the help of diagram, how the refraction of light takes place through a glass prism.
Answer :

The incident ray I when enters the prism it gets refracted, bends and form ∠ r with the normal. Angle of refraction is smaller than the angle of incidence. The incident ray bends towards the normal, as it passes from rarer medium to denser medium. When this refracted ray passes from denser medium to rarer medium it bends away from the normal. This emergent ray has bent out at an angle to the direction of incident ray.
This angle is called the angle of deviation ∠D.

More Questions

1. What happens to the image distance in the eye when we increase the distance of an object from the eye?

2. A student has difficulty in reading the black board while sitting in the last row. What would be the defect the student is suffering from? How can it be corrected? 

3. A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the nature of the corrective lens used to restore proper vision? 

4. A person is able to see objects clearly only when these are lying at distances Between 50 cm and 300 cm from his eye.

(a) What kind of defects of vision is he suffering from?

(b) What kind of lenses will be required to increase his range of vision from 25 cm to infinity? Explain briefly. 

5. A beam of white light is passed through a hollow prism, will it produce a spectrum? 

6 Complete the given figure.

7. You are asked to set up traffic lights for a railway station, why would you choose red as the danger signal?

8.If p represents a person on earth then what does the line ab represent? What should be the minimum distance of the sun from ‘ab’ so as to enable ‘p’ to see its image? 

9. Do all people looking at a star, locate it at the same apparent position? If not explain. 

10.What will be observed when a screen is placed at A and at B. 

11. When a torch light is focussed on the eye which cells get activated immediately?

a) Sensory cells b) light sensitive cells

c) Cells of the ciliary muscles d) cells at the blind spot 

12. The defect in vision developed due to gradual weakening of ciliary muscle and diminishing flexibility of eye lens is:

a) Myopia b) hypermetropia c) night blindness d) presbyopia 

Question. Why do different colors deviate through different angles on passing through a prism?

Question. How is amount of light entering the eye is controlled?

Question. Under very dim light we are able to see the object but cannot distinguish between colors. Why?

Question. Draw a ray diagram to show the refraction of light through a glass prism and on the diagram mark (1) Incident ray (2)  mergent ray (3) Angle of deviation.

Question. The near point of a hyper metropic eye is 75cm from the eye. What is the power of the lens to enable him to read clearly a book held at 25cm from the eye?