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

## The Human Eyes And The Colorful World Exercise 269

Convex lens

### Solution 2

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

### Solution 3

(a) Iris

(b) Retina

(c) Ciliary muscles

(a) Cornea

(b) Retina

At retina

### Solution 6

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

### Solution 7

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

### Solution 8

The pupil of our eye contracts.

Retina

Blind spot

Retina

Rods and cones

## The Human Eyes And The Colorful World Exercise 270

(a) Cones

(b) Rods

True

### Solution 15

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

At cornea

Ciliary muscles

### Solution 18

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

### Solution 19

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

### 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.

### Solution 21

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

Ciliary muscles

### 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.

### Solution 24

(a) Optic nerve

(b) Ciliary muscles

(c) Pupil

(d) Cornea

(e) Eye lens

(a) cornea

(b) retina

(c) iris

(d) large

(e) light

(f) eye-lens

(g) thinner

(h) thicker

### 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.

### Solution 27

(a) Eye-lens becomes thicker.

(b) Eye-lens become thinner.

### Solution 28

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

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

### Solution 29

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.

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.

### 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.

### 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.

### 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.

## The Human Eyes And The Colorful World Exercise 271

### Solution 33

(a) Pupil becomes smaller.

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

### 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.

### 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.

### Solution 36

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

(b) They are called rods and cones.

(c) Rods are sensitive to dim light and cones are sensitive to bright light and colours.

### 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.

### 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.

### Solution 39

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

(ii) in bright light, puoil becomes small.

(b) (i) Cones

(ii) Rods

(iii) Cones

(a)