Class 10 Science Chapter 11 The Human Eye and the Colourful World The answer to each chapter is provided in the list so that you can easily browse throughout different chapters NCERT Class 10 Science Chapter 11 The Human Eye and the Colourful World and select need one.
Class 10 Science Chapter 11 The Human Eye and the Colourful World
Also, you can read the SCERT book online in these sections Solutions by Expert Teachers as per SCERT (CBSE) Book guidelines. These solutions are part of SCERT All Subject Solutions. Here we have given Assam Board Class 10 Science Chapter 11 The Human Eye and the Colourful World Solutions for All Subjects, You can practice these here…
The Human Eye and the Colourful World
Chapter – 11
GENERAL SCIENCE
TEXTUAL QUESTIONS AND ANSWERS
Page -190
Q.1. What is the meant by power of accommodation of the eye?
Ans :- The ability of the eye to fours both near and distant objects, by adjusting its focal length is called the power of accommodation of the eye.
Q.2. A person with a myopic eye cannot see objects beyond 1.2 m distinctly. What should be the type of the corrective lens used to restore proper vision?
Ans :- Diverging or concave lens.
Q.3. What is the far point and near point of the human eye with normal vision?
Ans :- The farthest point upto which the eye can see objects clearly is called the far point of the eye.
The minimum distance, at which objects can be seen most distinctly without strain is called the near point of the eye.
Q.4. A student has difficulty reading the black board while sitting in the last row. What could be the defect the child is suffering from? How can it be corrected?
Ans :- The student is suffering from myopia. He should be use concave lenses of suitable focal length.
EXERCISES
Q.1. 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 ) Far-sightedness.
Ans :- ( b ) Accommodation.
Q.2. The human eye forms the image of an object at its-
( a ) Cornea.
( b ) Iris.
( d ) Retina.
Ans :- ( d ) Retina.
Q.3. 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
Ans :- ( c ) 25 cm.
Q.4. 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.
Ans :- ( c ) Ciliary muscles.
Q.5. A person needs a lens of power -5.5 diopters for correcting his distant vision. For correcting his near di vision he needs a lens What is od ji the focal length of he lens required for correcting
( i ) Distant vision and
( ii ) Near vision?
Ans :- ( I ) Here p = –5.5 D
f = ?
We have, p = 1/f
⇒ f = 1/p
= 1/-5.5D
Q.8. Why is a normal eye not able to see clearly the objects idpiln placed closer than 25 cm?
Ans :- A distance less than 25 cm, the ciliary muscles can not bulge the eye less any more, the object cannot be focussed on the retina and it appears blurred to the eye.
Q.9. What happens to the image distance in the eye when we increase the distance of an object from the eye?
Ans :- In the eye, the image distance is fixed which cannot be changed. So, when we increase the distance of an object from the eye. There is no change in the image distance inside the eye.
Q.10. Why do stars twinkle?
Ans :- The twinkling of a star is due to atmospheric refraction of starlight. The starlight, on entering the earth’s atmosphere, undergoes refraction continuously before it reaches the earth. The atmospheric refraction occurs in a medium of gradually changing refractive index. Since the atmosphere bends light 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.
Further, this apparent position of the star is not stationary but keeps on changing slightly, since the physical conditions of the earth’s atmosphere are not stationary. Since the stars are very distant, they approximate point sized sources of light. As the part of rays of light coming from the star goes on varying slightly. The apparent position of the star fluctuates and the amount of starlight entering the eye flickers – the star sometimes appears brighten and at some other time fainter, which is the twinkling effect.
Q.11. Explain why the planets do not twinkle.
Ans :- The planets are much closer to the earth and are extended sources. If we consider a planet as a collection of a large us seen as number of point sized sources of light, the total variation in the amount of light entering our from all the individual point-sized sources will average out to zero. There by nullifying the twinkling effect.
Q.12. Why does the Sun appear reddish early in the morning?
Ans :- The sun and the surrounding sky appear red at sun rise because at that time most of the blue colour present in sunlight has been scattered out and away from our line of sight, leaving behind mainly red colour in the direct sunlight beam that reaches our eyes.
Q.13. Why does the sky appear dark instead of blue to an astronaut?
Ans :- This is because in outer space, there is no atmosphere to scatter sunlight. Since there is no scattering of blue component of white sunlight which ca reach the eyes of an astronaut in outer space, therefore the sky appears dark to the astronaut instead of blue.
Additional Questions
Q.1. What are the main parts of human eye?
Ans :- The main parts of human eye are :- Cornea, Iris, Pupil, Ciliary muscles, Eye lines, Retina and Optic nerve.
Q.2. Name the part of the eye :
( a ) Which control the amount of light entering the eye.
( b ) On which the image is formed.
( c ) Which changes the focal length of eye lens.
Ans : ( a ) Iris.
( b ) Retina.
( c ) Ciliary muscles.
Q.3. What is the name of
( a ) The curved, transparent front surface of the eye?
( b ) The light-sensitive layer in the eye?
Ans :- ( a ) Cornea.
( b ) Retina.
Q.4. Give the scientific names of the following parts of the eye :
( a ) Carries signals from an eye to the brain.
( b ) Muscles which change the shape of the eye-lens.
( c ) A hole in the middle of the iris.
( d ) A clear window at the front of the eye.
( e ) Changes shape to focus a picture on the retina.
Ans :- ( a ) Optic nerve.
( b ) Citeary muscles.
( c ) Pupil.
( d ) Cornea.
( e ) Eye lens.
Q.5. Define the following :
( a ) Myopia.
( b ) Hypermetropia.
( c ) Presbyopia.
( d ) Cataract.
Ans :- ( a ) Myopia :- Myopia is that defect of vision due to which a person cannot see the distant objects clearly though he can see the nearby objects clearly.
( b ) Hypermetropia :- Hypermetropia is that defect of vision due to which a person cannot see the nearby objects clearly though he can see the distant objects clearly.
( c ) Presbyopia :- Presbyopia is that of vison due to which an old person cannot see the nearby objects clearly due to loss of power of accommodation of the eye.
( d ) Cataract :- The medical condition in which the lens of the eye of a person becomes progressively cloudy resulting in blurred vision is called cataract.
Q.6. State whether the following statement is true or false : Short-sightedness can be cured by using a concave lens.
Ans :- True.
Q.7. Name one defect of vision which cannot be corrected by any type of spectacle lenses.
Ans :- Cataract.
Q.8. A short-sighted person has a near point of 15 cm. and a far point of 40 cm.
( a ) Can he see clearly an object at a distance of :
( i ) 5 cm?
( ii ) 25 cm?
( iii ) 50 cm?
Ans :- ( i ) No.
( ii ) Yes.
( iii ) No.
( b ) To see clearly an object at infinity, what kind of irba spectacle lenses does he need?
Ans :- Concave lenses.
( c ) In the formation of spectrum of white light by a prism:
( i ) Which colour is deviated least ?
( ii ) Which colour is deviated most?
Ans :- ( i ) Red.
( ii ) Violet.
Q.10. Name the phenomenon which causes the twinkling of stars.
Ans :- Atmospheric refraction of light.
Q.11. What is Tyndall Effect?
Ans :- The scattering of light by particles in its path is called Tyndall effect.
Q.12. Why the sky is blue?
Ans :- The scattering of blue component of the while sunlight by air molecules present in the atmosphere causes the blue colour of the sky.
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