LAKHMIR SINGH AND MANJIT KAUR Solutions for Class 10 Physics Chapter 6 - The Human Eyes And The Colorful World

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Chapter 6 - The Human Eyes And The Colorful World Exercise 269

Question 1

What kind of lens is present in the human eye?

Solution 1

Convex lens

Question 2

Name two parts of the eye which refract light rays(or bend light rays).

Solution 2

Two parts which refract light rays are cornea and eye-lens.

Question 3

Name the part of the eye:

(a) Which controls the amount of light entering the eye

(b) On which the image is formed

Solution 3

(a) Iris

(b) Retina

Question 4

What is the name of:

(a) The curved, transparent front surface of the eye?

(b) The light- sensitive layer in the eye?

Solution 4

(a) Cornea

(b) Retina

Question 5

Where is the image formed in a human eye?

Solution 5

At retina

Question 6

What is the function of the lens in the human eye?

Solution 6

Eye lens changes its shape and thickness to focus light on to the retina.

Question 7

What job does the pupil of the eye do?

Solution 7

Pupil expands or contracts according to the intensity of light around the eye.

Question 8

How does the eye adjust to take account of an increase in brightness?

Solution 8

The pupil of our eye contracts.

Question 9

Name that part of the eye which is equivalent to the photographic film in a camera.

Solution 9

Retina

Question 10

Name that part of the retina which is insensitive to light.

Solution 10

Blind spot

Question 11

Which part of the eye contains cells which are sensitive to light?

Solution 11

Retina

Question 12

Name two types of cells in the retina of an eye which respond to light.

Solution 12

Rods and cones

Chapter 6 - The Human Eyes And The Colorful World Exercise 270

Question 13

Out of rods and cones in the retina of your eye:

(a) Which detect color?

(b) Which work in dim light?

Solution 13

(a) Cones

(b) Rods

Question 14

State whether the following statement is true or false:

The image formed on our retina is upside - down.

Solution 14

True

Question 15

What is the principal function of the eye - lens?

Solution 15

The principal function of the eye-lens is to focus light on to the retina.

Question 16

Where does the greatest degree of refraction of light occur in the eye?

Solution 16

At cornea

Question 17

What changes the shape of lens in the eye?

Solution 17

Ciliary muscles

Question 18

What do the ciliary muscles do when you are focusing on a nearby object?

Solution 18

The ciliary muscles make the eyes lens thicker (more converging).

Question 19

What is the least distance of distinct vision for a normal human eye?

Solution 19

The least distance of the distinct vision for a normal human eye is about 25cm.

Question 20

What is the:

(a) Far point of a normal human eye?

(b) Near point of a normal human eye?

Solution 20

(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.

Question 21

What is the range of vision of a normal human eye?

Solution 21

Range of vision of a normal human eyes is from infinity to about 25cm.

Question 22

Name the part of our eyes which helps us to focus near and distinct objects in quick succession.

Solution 22

Ciliary muscles

Question 23

Define the term "power of accommodation" of human eye.

Solution 23

The ability of an eye to focus the distant objects as well as the nearby objects on the retina by changing the focal length of its lens is called the power of accommodation.

Question 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

(d) A clear window at the front of the eye

(e) Changes the shape to focus a picture on the retina

Solution 24

(a) Optic nerve

(b) Ciliary muscles

(d) Cornea

(e) Eye lens

Question 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 of light 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 ___

Solution 25

(a) cornea

(b) retina

(d) large

(e) light

(f) eye-lens

(g) thinner

(h) thicker

Question 26

Why is the normal eye not able to see clearly the objects placed closer than 25 cm?

Solution 26

The normal eye is not able to see clearly the objects placed closer than 25 cm because all the power of accomodation of the eye is exhausted at a distance of 25 cm. The maximum accomodation of the eye is reached when the object is placed at 25 cm fro the eye. After this the ciliary muscles cannot make the eye-lens more thick.

Question 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?

Solution 27

(a) Eye-lens becomes thicker.

(b) Eye-lens become thinner.

Question 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 covering power of eye-lens will be the maximum?

Solution 28

(a) When the eye is focused on a distant object.

(b) When the eye is focused on a nearby object.

Question 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.

Solution 29

Question 30

How is the amount of light entering the eye controlled?

Solution 30

The amount of light entering the eye is controlled by the iris. It automatically adjusts the size of the 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.

Question 31

What happens to the eye when you enter a darkened cinema hall from bright sunshine? Give reason for your answer.

Solution 31

When we enter a darkened cinema hall from bright sunshine, at first we cannot see anything clearly. After a short time our vision improves. This is because 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.

Question 32

Why does it take some time to see objects in a dim room when you enter the room from bright sunshine outside?

Solution 32

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.

Chapter 6 - The Human Eyes And The Colorful World Exercise 271

Question 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?

Solution 33

(a) Pupil becomes smaller.

(b) The amount of light entering the eye is reduced.

Question 34

Ciliary muscles of human eye can contract or relax. How does it help in the normal functioning of the eye?

Solution 34

Ciliary muscles get relaxed and the eye lens becomes thin when the eye is looking at a distant object, and these muscles contract and make the eye-lens thick when the eye is looking at a nearby object. Thus, ciliary muscles help in the normal functioning of the eye by changing the thickness of the eye-lens while focussing.

Question 35

Describe and explain, how a normal eye can see objects lying at various distances clearly.

Solution 35

To focus on distant objects, the ciliary muscles of the eye get fully relaxed and pull the suspensory ligaments attached to the eye-lens tightly. This, in turn, 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.

To focus on nearby objects, the ciliary muscles of the eyes contract and make the suspensory ligaments 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.

Question 36

There are two types of light-sensitive cells in the human eye:

(a) Where are they found?

(b) What is each type called?

Solution 36

(a) The two types of light-sensitive cells are found in the retina.

(b) They are called rods and cones.

Question 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?

Solution 37

Rods are the rod-shaped cells present in the retina of an eye which are sensitive to dim light.

Cones are the cone-shaped cells present in the retina of an eye which are sensitive to bright light.

Our night vision is relatively poor compared to the night vision of an owl due to the presence of relatively smaller number of rod cells in the retinas of our eyes.

Question 38

(a) How does the convex eye-lens differ from the ordinary convex lens made of glass?

(b) List, in order, the parts of the eye through which light passes to reach the retina.

Solution 38

(a) 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.

(b) Cornea, pupil, eye-lens, retina.

Question 39

(a) What happens to the size of pupil of our eye (i) in dim light (ii) in bright light?

(b) Name the cells on the retina of an eye which are sensitive to (i) bright light (ii) dim light (iii) sensation of colour.

Solution 39

(a) (i) In dim light, pupil becomes large.

(ii) in bright light, puoil becomes small.

(b) (i) Cones

(ii) Rods

(iii) Cones

Question 40

(a) Draw a simple diagram of the human eye and label clearly the cornea, iris, pupil, ciliary muscles, eye-lens retina, optic nerve and blind spot.

(b) Describe the working of the human eye with the help of the above diagram.

Solution 40

(a)

(b) Working of the human eye

The light rays coming from the object kept in front of the eye enter the cornea, pass through the pupil and fall on the eye lens. The eyes lens is convex lens, so it converges the light rays and produces a real and inverted image of the object on the retina. The image formed on the retina is conveyed to the brain by the optic nerve and gives rise to the sensation of vision.

(c) The eye adjusts itself to deal with ight of vaying intensity with the help of the iris. The iris automatically adjusts the size of the pupil according to the intensity of light received by the eye. If the intensity of light is large, then iris contracts the pupil and reduces the amount of light entering the eye. And, if the intensity of light is small, then iris expands the pupil so that more light may enter the eyes.

Question 41

(a) Explain the functions of the following parts of the eye:

(a) cornea (b) iris (c) pupil (d) ciliary muscles

(e) eye-lens (f) retina (g) optic nerve

(b) If you walk from a dark room into sunlight and back again into dark room, how would your pupils alter in size? What makes this happen?

(c) Explain why, we cannot see our seats first when we enter a darkened cinema hall from bright light but gradually they become visible.

Solution 41

(a) a. Cornea: It is the fromt part of the eye. The light coming from objects enters the eye through cornea.

b. Iris: It controls the amount of light entering the eye.

c. Pupil: It controls the illumination in the eye.

d. Ciliary muscles: The focal length of the eye-lens can be changed by changing its shape by the action of ciliary muscles.

e. Eye-lens: It focuses light on to the retina.

f. Retina: It is a delicate membrane having a large number of light sensitive cells called 'rods' and 'cones' which respond to the intensity of light and colour of objects respectively.

g. Optic nerve: It conveyes the image formed on the retina to the brain.

(b) If we walk from a dark room into sunlight, the pupil of the eye contracts. On again entering the dark room, the pupil of the eye expands.

(c) When we enter a darkened cinema hall from bright sunshine, at first we cannot see our seats clearly but gradually they become visible. This is because 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.

Chapter 6 - The Human Eyes And The Colorful World Exercise 272

Question 53

The descriptions of five kinds of images are given below:

(a) diminished and virtual (b) enlarged and real

(e) virtual and the same size

Which one of these describes the image formed :

(i) On the retina of the eye?

(ii) by a magnifying glass?

(iii) By a convex driving mirror on a car?

(iv) By a plane mirror?

(v) On the screen of a slide projector?

Solution 53

(i) d

(ii) c

(iii) a

(iv) e

(v) b

Question 54

What shape are your eye-lenses:

(a) when you look at your hand?

(b) when you look at a distant tree?

Solution 54

(a) Thick

(b) Thin

Question 55

Suggest how your irises help to protect the retinas of your eyes from damage by bright light.

Solution 55

Irises help to protect the retinas of our eyes from damage by bright light by adjusting the size of the pupil according to the intensity of light received by the eye.

Question 56

(a) Which parts of the eye cause rays of light to converge on the retina?

(b) Which part causes the greatest convergence?

Solution 56