CBSE Class 10 Science Chapter-11 Human Eye and Colourful World – Free PDF Download
Free PDF download of Important Questions with Answers for CBSE Class 10 Science Chapter 11 – Human Eye and Colourful World prepared by expert Science teachers from latest edition of CBSE(NCERT) books only by CoolGyan to score more marks in CBSE board examination.
CBSE Class 10 Science Chapter-11 Human Eye and Colourful World Important Questions
CBSE Class 10 science Important Questions Chapter 11 – Human Eye and Colourful World
3 Mark Questions
1. (a) What is hypermetropia?
(b) What are the two causes of this defect of vision?
Ans. (a) Hypermetropia is the defect in which a person can see distant objects clearly but cannot see the nearby objects.
(b) The two possible causes of this defect are
(i) Increase is the focal length of the eye lens
(ii) Eye ball gets shortened
2. (a) What is scattering of light?
(b) Astronauts observe the sky as dark instead of blue why?
Ans. (a) The re-scattering of light by the scatterers present is the atmosphere in different directions after being absorbed by them is called scattering.
(b) The blue of sky is due to scattering of blue colour by the earth’s atmosphere. For the astronaut there would be no such scattering effect. Hence the sky appears dark to the astronaut.
3. A person is known to use a lens of power
(i) -5.5 D for his distant vision
(ii) +1.5 D for his near vision
Calculate the focal length of the lens used for correcting his
(a) Distant vision and (b) Near vision problems.
Ans. (i) For distant vision
(ii) For near vision
4. What is presbyopia? State the causes of this defect? How is presbyopia of a person corrected?
Ans. Presbyopia is the defect of human eye in which a person is unable to see the nearby as well as far off objects clearly.
Causes:
(1) Decrease is the power of accommodation of the eye due to ageing
(2) Weakening of the ciliary muscles It can be corrected by using a bifocal lens (upper half concave and the lower half convex)
5. The rainbow is a natural spectrum appearing in the sky after a rain shower
(a) Is it correct to say that a rainbow is always formed in a direction opposite to sun?
(b) Can it be seen on a sunny day?
(c) Arrange the sequence in correct sequential order Refraction, Internal Reflection, Refraction & Dispersion
Ans. (a) Yes
(b) No, we cannot observe a rain bow on a sunny day when we look at the sky through a waterfall
or fountain with the sun behind us.
(c) Refraction and dispersion, internal reflection, Refraction.
6. (a) Write two causes of hypermetropia?
(b) Show diagram to show the correctness of hypermetropia?
Ans. (a) Causes of hypermetropia
(1) Increase in the focal length of the eye lens
(2) Decrease in the size of the eye ball.
(b)
7. A reporter records the following observations of an astronaut from his space ship.
(a) The length of the day is same as observed on the earth.
(b) Sky appears black in colour.
(c) The star appears to twinkle while the planets do not do so as they do on the earth.
Justify each statement
Ans. (a) It is incorrect as length of the day in space would be about four minutes shorter than that on the earth.
(b) It is correct because in space we cannot observe scattering of light because of absence of atmosphere.
(c) It is incorrect because twinkling of stars is due to atmospheric refraction but in space we do not have atmosphere and atmospheric particles.
8. A person needs a lens of power -5.5 dioptre for correcting his distinct vision. For correcting his near vision he needs a lens +1.5 dioptre. What is the focal length of the lens required for correcting (i) distinct vision, and (ii) near vision?
Ans. (i) Power of lens needed for correction distant vision of the person (P) = -5.5 D
Focal length of lens required for correcting distant vision (f)
= 1/P = 1/-5.5 m = 0.18 m = 18 cm.
(ii) For correcting near vision the power of lens required (P) = +1.5 D
Focal length of lens required for correcting near vision (f)
= 1/P = 1/1.5 m = 0.67 m = 66.7 cm.
9. Why do stars twinkle?
Ans. Stars twinkle due to atmospheric refraction of starlight. As the stars are very away they behave as almost point sources of light. As on account of atmospheric refraction, the path of rays of light coming from the star goes on varying slightly, the apparent position of the star fluctuates and the amount of light entering the eye flickers, so sometimes the star appear brighter and at some other time, fainter. Thus the stars twinkle.
10. Explain why the planets do not twinkle.
Ans. Planets are much closer to the earth and are seen as extended source. So, a planet may be considered as a collection of a large number of point-sized light sources. Although light coming from individual point-sized sources flickers but the total amount of light entering our eye from all the individual point-sized sources average out to be constant. Thereby, planets appear equally brighter and there is no twinkling of planets.
11. Why does the sky appear dark instead of blue to astronaut?
Ans. Blue colour of the sky is on account of scattering of light of shorter wavelength by particles in the atmosphere of earth. If the earth had no atmosphere, there would not have been any scattering and sky would have looked dark. When astronaut in his spacecraft goes above the atmosphere of earth, sky appears dark to him because there is no scattering of light.
12. A certain person has minimum distance of distinct vision of 150cm . He wishes to read at a distance of 25cm. What focal length glass should he use? What is the nature of eye defect?
Ans. -U=-25 cm V=-l5O cm.
1/f= 1
1/f=1/ – 1/(-25)
f=3Ocm.
f being +ve, lense used is convex lens.
Hypermetropic
