DAV Class 8 Science Chapter 11 The Human Eye Solutions

DAV Class 8 Science Chapter 11 The Human Eye

The DAV Class 8 Science Chapter 11 The Human Eye Solutions of The Living World Science Book is extremely crucial for the students studying in DAV Class 8. The DAV Solutions for Class 8 Science of Chapter 11 The Human Eye are provided here to help the students to clear all their doubts and to help them in understanding the chapter in an easy and interesting way.

These DAV Solutions present you with answers to the question on the Human eye, how do we see colours? Working of the human eye, care of the eye, visually challenged persons, braille system in details.

While solving the DAV textbook questions, students often face several doubts and eventually get confused. To help the students clear all their doubts instantly, the DAV Class 8 Science Chapter 11 The Human Eye Solutions come as a great resource. Here, the detailed Solutions for Class 8 Science Chapter 11 of DAV Class 8 Science book are given.

DAV Class 8 Science Chapter 11 The Human Eye Question Answer

DAV Class 8 Science Chapter 11 The Human Eye Question Answer is given below. Here DAV Class 8 Science Chapter 11 Question Answer is provided with great explanation.

Highlights

• Fill in the blanks
• True or False
• Tick the correct option
• Answer the following questions in brief
• Answer the following questions

These DAV Class 8 Science Chapter 11 The Human Eye Solutions will help you in scoring good marks as they cover important concepts in different patterns like fill in the blanks, True or False, tick the correct option, short answer questions, long questions answer and more.

A. Fill in the blanks.

1. The ___________ of the human eye determines the colour of a person’s eye.

2. The light sensitive screen of the human eye is called ___________.

3. The cone-shaped cells, on the retina, respond to the ___________.

4. The defect of vision, in which eyeball becomes smaller than its normal size, is called ___________.

5. A ___________ lens is used to correct myopia and a ___________ lens is used to correct hypermetropia.

Answer: (1) iris (2) retina (3) bright light (4) hypermetropia (5) concave, convex

B. Write True or False for the following statements.

1. Iris is the muscular assembly that controls the size of the pupil.

2. The eye lens forms a virtual, erect and diminished image of an object, on the retina.

3. The retina of the human eye has a large number of cone-shaped and rod-shaped cells. The rods can respond even in dim light.

4. Cinematography makes use of the persistence of vision of the human eye.

5. For a normal human eye, the range of vision is from (nearly) 25 cm to infinity.

6. Myopia is caused due to excessive curvature of the cornea.

Answer: (1) True (2) False (3) True (4) True (5) True (6) True

C. Tick the correct option.

1. The change in focal length of an eye lens, to focus the image of objects at varying distances, is brought about by the action of-

Answer: ciliary muscles

2. The impression of the image formed on the retina of the human eye remains there for about-

Answer: 1/16^th second

3. The human eye can focus objects at different distances by adjusting the focal length of the eye lens. This ability of the eye is known as-

Answer: power of accommodation

4. A near sighted person will face difficulty while reading-

Answer: a street signboard across the street.

5. The defect of the human eye, in which the eye lens of a person gets progressively cloudy, resulting in blurred vision, is called-

Answer: cataract

6. The Braille system, for visually challenged persons, is a-

Answer: tactual aid

D. Answer the following questions in brief.

1. Name the part of the human eye which acts as a protective layer for the eye.

Answer: Cornea

2. The pupil appears black. Why?

Answer: It appears black as no light is reflected from it.

3. Differentiate between:

(a) rod-shaped and cone-shaped cells

Answer:

rod-shaped cell	cone-shaped cells
The rod-shaped cell gets activated in both bright and dim light conditions.	The cones-shaped cells get activated only in bright light conditions.
These cells do not help us in colour vision.	These cells help us in colour vision.

(b) near point and far point of human eye

Answer:

4. State the difference between:

(a) myopia and hypermetropia

Answer:

(b) tactual aids and auditory aids

Answer:

Tactual aids	Auditory aids
Tactual aid work on the touch receptors i.e., skin.	Auditory aids rely on our ability to hear.
Braille system is an example of tactual aids.	Audio caste is an example of auditory aid.

5. Define the terms:

(a) Blind spot on the retina

Answer: A point on the retina which is insensitive to light is called blind spot on the retina. This is the spot where the optic nerve meets the retina.

(b) Persistence of vision of human eye

Answer: The ability of the human eye to continue to see the image of an object for a very short duration even after the object has disappeared from the view. This (brief) continuence, of the sensation of vision, is called persistence of vision.

6. Give the meaning of the terms:

(a) Power of accommodation of the human eye

Answer: Power of accommodation is the special property of the human eye to adjust the focal length to see the object clearly.

(b) Least distance of distinct vision

Answer: The minimum distance, at which objects can be seen most distinctly (without strain), is called the least distance of distinct vision, or near point, of the eye.

(c) Range of vision

Answer: The distance, between the near point and far point of a normal eye, is called its range of vision.

7. What happens to the image distance in the eye when the distance of the object from the eye increases?

Answer: when the distance of the object from the eye increases the image distance in the eye will always be same. In every case, image is formed on the retina due to the power of accommodation.

8. When Sahil tried to read a book by keeping it at a distance of 25 cm, the text print appeared to be blurred.

(a) Is the image of the text getting formed before the retina, or beyond the retina of his eye?

Answer: Beyond the retina.

(b) What conclusion can be drawn about the least distance of distinct vision’ of Sahil’s eye?

Answer: the least distance of distinct vision’ of Sahil’s eye has increased as he is suffering from hypermetropia.

9. A person, with a myopic eye, cannot see objects beyond 1.2 m distinctly. What can be said about the likely size of his eyeball? State the nature of the corrective lens that is needed to restore his proper vision?

Answer: His eyeball has become elongated. He needs to use a concave lens to correct his vision defect.

E. Answer the following questions.

1. Draw a labelled sketch of the human eye. Explain the function of the following parts of the human eye: (a) cornea (b) iris (c) pupil (d) eye lens (e) ciliary muscles (f) retina (g) optic nerves.

Answer:

(a) cornea: Its main function is to act as a protective layer for the eye.

(b) iris: The iris is responsible for the characteristic colour of the eye of a person.

(c) pupil: Pupil is the self-adjustable aperture which regulates the amount of light entering the eye by adjusting its size.

(d) eye lens: The eye lens is a convex lens which focuses the rays of light on retina.

(e) ciliary muscles: These muscles help in changing the curvature and the focal length of the eye lens.

(f) retina: It is a light sensitive screen where image of the object is formed.

(g) optic nerves: Carries signals from the eye to the brain.

2. Explain how we perceive objects as they are.

Answer: Light coming from an object enters the eye through the cornea and pupil. The eye lens converges these light rays to form a real, inverted and diminished image of the object on the retina. The light sensitive cells of the retina get activated when light falls on them; they then generate electrical signals. These electric signals are sent to the brain by the optic nerves. The brain interprets the electrical signals in such a way that we see an image which is erect and of the same size as the object.

3. State any five precautions that are needed to take care of our eyes.

Answer: Five precautions that are needed to take care of our eyes are:

1. Gently wash eyes frequently with clean (potable) water.
2. Eat a balanced diet having lots of fruits and vegetables.
3. Never look at the sun, or any other powerful light source, directly.
4. Try not to spend too much time looking continuously at the computer screen, or television. It can cause eye strain.
5. Have sufficient light in the room when you are reading, writing or watching television.

4. Explain how optical and non-optical aids help visually challenged persons to develop their skills to a higher level.

Answer: Optical and non-optical aids help visually challenged persons to develop their skills to a higher level in this way:

Optical aids: These include lenses and telescopic aids. While suitable lens combinations are used to rectify visual limitations, the telescopic aids can help to view class demonstrations and the blackboard.

Non-optical aids: These often include (1) tactual aids (using sense of touch; the visually impaired can learn to read and write by using a special touch system called the Braille. This system makes use of raised dots (put on a paper) and (ii) auditory (using sense of hearing) aids include audio cassettes, tape recorders, audio CDs, audio books. Other electronic devices (like computer/calculator/closed circuit television) make use of software programmes that can transfer ‘text files’ into sound.

5. What is the Braille system? How does it help the visually challenged persons?

Answer: Braille is a coded language based on a logical system. There are Braille codes for common languages as well as, mathematical and scientific notations. Many languages (foreign/Indian) can be read using the braille system.

Braille system has 63 dot patterns or characters. The braille characters make up the letters of alphabet, punctuation marks, etc. Dots/Characters are arranged in cells of two vertical rows of three dots each. Patterns of dots, used to represent letters of the English alphabet. These patterns, when embossed on Braille sheets, help visually challenged person to recognise words by touching.