Solutions of The Human Eye and The Colourful World Lakhmir Singh Manjit Kaur VSAQ, and SAQ Pg No. 269 Class 10 Physics
1. What kind of lens is present in the human eye?
Answer
→ Convex lens is present in the human eye.
2. Name two parts of the eye which refract light rays (or bend light rays).
Answer
→ Two parts of the eye which refract light rays (or bend light rays) are Cornea and Eye-lens.
3. Name the part of the eye:
(a) Which controls the amount of light entering the eye.
(b) on which the image is formed.
(c) which changes the focal length of eye.
Answer
→ (a) The part of the eye which controls the amount of light entering the eye is iris.
(b) the part of the eye on which the image is formed is retina.
(c) the part of the eye which changes focal length of eye-lens is ciliary muscles.
4. What is the name of:
(a) the curved, transparent front surface of the eye ?
(b) the light-sensitive layer in the eye?
Answer
→ (a) The name of the curved, transparent surface is cornea.
(b) The name of the light-sensitive layer in the eye is retina.
5. Where is the image formed in a human eye?
Answer
→ The image formed in a human eye at retina.
6. What is the function of the lens in the human eye?
Answer
→ The major function of the lens in the human eye is to change its shape and thickness to focus light on the retina.
7. What job does the pupil of the eye do?
Answer
→ According to the intensity of light around the eye, Pupil expands or contracts.
8. How does the eye adjust to take account of an increase in brightness?
Answer
→ The pupil of our eye contracts to adjust the eye to take account of an increase in brightness.
9. Name that part of the eye which is equivalent to the photographic film in a camera.
Answer
→ The part of the eye which is equivalent to the photographic film in a camera is retina.
10. Name the part of the retina which is insensitive to light.
Answer
→ The part of the retina which is insensitive to light is blind spot.
11. Which part of the eye contains cells which are sensitive to light?
Answer
→ Retina contains cells which are sensitive to light.
12. Name two types of cells in the retina of an eye which respond to light.
Answer
→ The two types of cells in the retina of an eye which respond to light are Rods and Cones.
13. Out of rods and cones in the retina of your eye:
(a) which detect color?
(b) which work in dim light?
Answer
→ (a) Cones detect color.
(b) Rods work in dim light.
14. State whether the following statement is true or false: The image formed on our retina is upside-down.
Answer
→ True, The image formed on our retina is upside-down.
15. What is the principal function of the eye-lens?
Answer
→ To focus light on to the retina is the main function of the eye lens.
16. Where does the greatest degree of refraction of light occur in the eye?
Answer
→ The greatest degree of refraction of light occur in the eye at cornea.
17. What changes the shape of lens in the eye?
Answer
→ Ciliary muscles changes the shape of lens in the eye.
18. What do the ciliary muscles do when you are focusing on a nearby object?
Answer
→ The ciliary muscles make the eye-lens thicker (more converging) when you are focusing on a nearby object.
19. What is the least distance of distinct vision for a normal human eye ?
Answer
→ 25cm is the least distance of vision for a normal human eye.
20. What is the:
(a) far point of a normal human eye?
(b) near point of a normal human eye?
Answer
→ (a) The far point of a normal human eye is at infinity.
(b) The near point of a normal human eye is at 25cm from the eye.
21. What is the range of vision of a normal human eye?
Answer
→ The range of vision of normal human eye is from 25cm to infinity.
22. Name the part of our eyes which helps us to focus near and distant objects in quick succession.
Answer
→ The part of our eyes which helps us to focus near and distant objects in quick succession is ciliary muscles.
23. Define the term "power of accommodation" of human eye.
Answer
→ The term "power of accommodation" of human eye refers to the ability of an eye to focus the distance objects as well as the nearby objects on the retina by changing the focal length of its lens.
24. 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.
Answer
→ (a) The scientific name for the part of the eye which carries the signals from the eye to the brain is called optic nerve.
(b) The muscle which changes the shape of the eye-lens is known as ciliary muscles.
(c) A hole in the middle of the iris is known as pupil.
(d) A clear window at the front of the eye is known as cornea.
(e) Eye-lens changes shape to focus a picture on the retina.
25. Fill in the following blanks with suitable words:
(a) Most of the refraction of light rays entering the eye occurs at the outer surface of the _______
(b) The part of eye sensitive to light is_______
(c) The part of eye which alters the size of the pupil is_______
(d) When light is dim, the pupil becomes_______
(e) The iris controls the amount of_______entering the eye.
(f) The ciliary muscles control the shape of the _______
(g) To bring light from a distant object to a focus on the retina of the eye, the convex eye-lens needs to be made_______
(h) To bring light from a near object to a focus on the retina of the eye, the convex eye-lens needs to be made_______
Answer
→ (a) Most of the refraction of light rays entering the eye occurs at the outer surface of the cornea.
(b) The part of eye sensitive to light is retina.
(c) The part of eye which alters the size of the pupil is iris.
(d) When light is dim, the pupil becomes larger.
(e) The iris controls the amount of light entering the eye.
(f) The ciliary muscles control the shape of the eye-lens.
(g) To bring light from a distant object to a focus on the retina of the eye, the convex eye-lens needs to be made thinner.
(h) To bring light from a near object to a focus on the retina of the eye, the convex eye-lens needs to be made thicker.
Short Answer Type Questions-Pg-270
26. Why is a normal eye not able to see clearly the objects placed closer than 25 cm?
Answer
→ All the power of accommodation of the eye is exhausted at a distance of 25 cm. The maximum accommodation of the eye is reached when the object is placed at 25 cm from the eye. After this the ciliary muscles cannot make the eye-lens more thick. This is why a normal eye not able to see clearly the objects placed closer than 25 cm.
27. What changes take place in the shape of eye-lens :
(a) when the eye is focused on a near object?
(b) when the eye is focused on a distant object ?
Answer
→ (a) when the eye is focused on a near object eye-lens become thicker.
(b) When the eye is focused on a distant object the eye-lens becomes thinner.
28. The eyes of a person are focused (i) on a nearby object, and (ii) on a distant object, turn by turn. In which case:
(a) the focal length of eye-lens will be the maximum ?
(b) the converging power of eye-lens will be the maximum?
Answer
→ (a) The focal length of eye-lens will be the maximum when the eyes of a person are focused on a distant object.
(b) The converging power of eye-lens will be the maximum when the eye of a person is focused on a nearby object.
29. What change is made in the eye to enable it to focus on objects situated at different distances ? Illustrate your answer with the help of diagrams.
Answer
→ When the eye need to focus on any distance object, then in that case the ciliary muscles of the eye get fully relaxed and this also pull the ligaments attached to the eye-lens tightly. During this process the eye lens get stretched and the eye-lens becomes thin.
When the eye has to focus on the nearby objects, then in that case the ciliary muscles of the eye has to contract and make the suspensory ligaments loose. Which results in the ligaments to stop pulling the eye lens. The eye lens bulges under its own elasticity and hence the eye lens got thick.
30. How is the amount of light entering the eye controlled?
Answer
→ The part of eye which control the amount of light entering the eye is iris. It is responsible for the adjustment of pupil according to the intensity of light received by the eye. If the amount of light received by the eye is large, then the iris contracts the pupil and reduces the amount of light entering the eye. If the amount of light received by the eye is small, then the iris expands the pupil so that more light may enter the eye.
31. What happens to the eye when you enter a darkened cinema hall from bright sunshine? Give reason for your answer.
Answer
→ At first we cannot see anything clearly when we enter the cinema hall from bright sunshine outside. This just for a short period of time. After that our vision improves. The reason behind that is, in bright sunshine the pupil of our eye is small and when we just enter the darkened room very little light enters our eye due to which we cannot see properly. After a while, when the pupil of our eye expands, more light enters our eye and we can see clearly.
32. Why does it take some time to see objects in a dim room when you enter the room from bright sunshine outside?
Answer
→ Because of the intensity of the light entering the eye the pupil adjusts itself. This is the reason why it takes some time to see objects in a dim room when we enter the room from bright sunshine outside because it takes some time to the small pupil of our eye to become large so that more light enters our eye and we can see clearly.
33. A person walking in a dark corridor enters into a brightly lit room:
(a) State the effect on the pupil of the eye.
(b) How does this affect the amount of light entering the eye ?
Answer
→ (a) When a person walking in a dark corridor enters into a brightly lit room, the Pupil becomes smaller.
(b) When a person walking in a dark corridor enters into a brightly lit room, the amount of light entering the eye is reduced.
34. Ciliary muscles of human eye can contract or relax. How does it help in the normal functioning of the eye ?
Answer
→ When the eye is looking at a distant object the ciliary muscles get relaxed and the eye lens becomes thin, in the same way when the eye is seeing a nearby object these muscles contract and make the eye-lens thick. By changing the thickness of the eye lens while focusing the ciliary muscles helps in normal functioning of the normal human eye.
35. Describe and explain, how a normal eye can see objects lying at various distances clearly.
Answer
→ When an object is at a distance, the ciliary muscles of the eye get fully relaxed and pull the suspensory ligament attached to the eye-lens tightly. Which then, stretches the eye-lens and the eye-lens becomes thin. This thin eye-lens has large focal length and small converging power sufficient to converge the parallel rays of light coming from a distant object to form an image on the retina.
In the same way, to focus on nearby objects, there is contraction in the ciliary muscles and which make the suspensory ligament loose. The ligaments then stop pulling the eye-lens. The eye-lens bulges under its own elasticity and becomes thick. This thick eye-lens has small focal length and large converging power which converges the diverging rays coming from the nearby object to form an image on the retina.
36. There are two types of light-sensitive cells in the human eye:
(a) Where are they found ?
(b) What is each type called?
(c) To what is each type of cell sensitive?
Answer
→ (a) There are two types of light-sensitive cells in the human eye and are found in the retina.
(b) There are two types of light-sensitive cells in the human eye and they are called rods and cones.
(c) For dim light rods are sensitive and for the bright light and colors cones are sensitive.
37. What are rods and cones in the retina of an eye? Why is our night vision relatively poor compared to the night vision of an owl?
Answer
→ The rod shaped cells present in the retina of an eye is called rods these are sensitive to dim light.
The cone-shaped cells present in the retina of an eye is called cones and these are sensitive to the bright light.
Our night vision is relatively poor as compared to the night vision of an owl because the number of rods cells present in our eyes are relatively low in number.
38A. How does the convex eye-lens differ from the ordinary convex lens made of glass?
Answer
→ The convex eye-lens differ from the ordinary convex lens made of glass because the focal length of the convex eye-lens can be changed by the action of ciliary muscles, but the focal length of the ordinary convex lens made of glass is fixed.
38B. List, in order, the parts of the eye through which light passes to reach the retina.
Answer
→ The parts of the eye through which light passes to reach the retina are in order as follows Cornea, pupil, eye-lens, retina.
39A. What happens to the size of pupil of our eye
(i) in dim light (ii) in bright light ?
Answer
→ (i) the size of pupil of our eye becomes larger in dim light.
(ii) The size of pupil of our eye becomes small in bright light.
39B. Name the cells on the retina of an eye which are sensitive to
(i) bright light (ii) dim light (iii) sensation
Answer
→ (i) The cells on the retina of an eye which are sensitive to bright light is Cones.
(ii) The cells on the retina of an eye which are sensitive to the dim light is rods.
(iii) The cells on the retina of an eye which are sensitive to sensation is Cones.