Very Short Answer-Class 10 -Science Physics-Chapter 11:The Human Eye And The Colourful World

Class 10 -Science-Very Short Answer Physics-Chapter 11:The Human Eye And The Colourful World

Q1.  What is Presbyopia ?

Ans : Presbyopia is a kind of eye defect in old persons due to ageing. It happens due to decrease in flexibili ty of eye lens and weakening of ciliary muscles.

Q2 What is the role of pupil in a human eye?

Pupil regulates and controls the amount of light entering in the eyes.

Q3. How can change of size of eyeball be one of the reason for:

(a)  Myopic (b) Hypermetropic

Compare the size of eyeball with that of a normal eye in each case. How does this change of size affect the position of image in each case?

Ans : (a) The eye suffering from myopia, has long eye ball than that of normal eye due to which the retina is at a larger distance from the eye lens. This results in the formation of the image in front of the retina.

(b) The eye suffering from hypermetropia has short eye ball than that of normal eye due to which the retina is smaller distance from the eye lens. This results in the formation of the image behind the retina.

Q4. State the function of pupil and ciliary muscles.

Ans :a. Pupil controls the amount of light entering the eye.

b. Ciliary muscles help in accommodation of power of eye lens.

Q5. A child sitting in a classroom is not able to read clearly the writing on the blackboard.

a. Name the type of defect from which his eye is suffering.

b. With the help of a ray diagram show how this defect can be remedied.

Ans :   a. Myopia

b. Myopia can be remedied by using concave lens.

Q6. What is meant by persistence of vision?

Ans : On removing object seen, its impression persists on the retina for 1/ 16th second. The inability of human brain to perceive more than two images formed on the retina within interval of 1/16th of a second is called persistence of vision. In this case, both the images merge and give a sensation of continuity.

Q6. List four common defects of vision that can be corrected with the use of spectacles.

Ans:

(i) Myopia

(ii) Hypermetropia

(iii) presbyopia

(iv) Astigmatism.

Q7. (a) Explain how a normal human eye is able to see distinctly the object placed at a distance as well as those placed at a nearer distance.

(b)  What is the far point and near point of a normal human eye?

 Ans :(a) Ciliary muscles change the curvature of eye lens as per requirement of the eye. This changes the focal 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.

Q8. Explain why do stars twinkle and planets do not?

Ans :The light coming from star get refracted through the atmospheric layers. Due to this, the star appear slightly higher than its actual position. Since the densities of atmospheric layers changes frequently and hence the position of the star appear changes continuously stars are very distant point-sized objects. As the path of rays of light coming from star is continuously changes. So sometimes light enters into our eyes and some times it faints. This is twinkling of the star. Since planets are closer to us, their size is also big. Our eyes receive light from different points of the planets. Hence planets do not twinkle.

Q9. Name the part of the eye where image is formed by the eye lens. What is the nature of the image formed? How is this image sent to the brain?

Ans : Retina. Image on the retina is inverted and real. Optic nerve sends the image to the brain.

Q10. An old person is unable to see clearly nearby object as well as distant objects, (i) What defect of vision is he suffering from?

 (ii) What kind of lens will be required to see clearly the nearby as well as distant objects? Give reason.

Ans : (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.

Q11. Why does it take sometimes to see the objects in a dim room when we enter the room from bright sunlight outside?

Ans:

In bright sunlight, pupil of eye contracts to control the light. When we enter a dim room, pupil takes some time to expand to allow more light to see the objects clearly.

Q12. Why does the clear sky appear blue? How would the sky appear in the absence of earth’s atmosphere?

Ans :Scattering of light   where   is the wavelength of light, i.e. least wavelength will scatter more and vice versa. Blue colour light has shorter wavelength and hence scattered more than other colours. In space, there is no atmosphere hence no scattering of light happens in the space so space appears black.

Q13. Why do we observe difference in colours of the sun during sunrise, sunset and noon?

Ans : During the sunrise or sunset, the sun is at horizon. Most of the blue light and other light of shorter wavelength are scattered most. Only the longer wavelength (red) reaches to us. That’s why sun appears red during the sunrise or sunset.

At noon, the Sun appears white because it is at our head and all wavelength reaches to us due to little of the blue and violet colours are scattered due to least distance travelled by fight.

Q14. Why do we observe the seven colours when white light passes through a glass prism? Which component of white light deviates the least?

Ans :Since angle of deviation for different colour is different hence different colour suffers different deviation. Deviation for red colour is minimum.

Q15. (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 :(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.