Light Class 8 Extra Questions and Answers Science Chapter 16

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Class 8 Science Chapter 16 Extra Questions and Answers Light

Extra Questions for Class 8 Science Chapter 16 Light with Answers

Light Class 8 Extra Questions Very Short Answer Type

Question 1.
What is virtual image?
Answer:
The image formed at a position behind the plane mirror is called a virtual image.

Question 2.
Can virtual image be obtained on a screen?
Answer:
No, virtual image cannot be obtained on a screen.

Question 3.
How many images, does one mirror form?
Answer:
The plane mirror can form only one image.

Question 4.
What name is given to the small opening behind the cornea?
Answer:
The name of the small opening behind the cornea is pupil.

Question 5.
Name the coloured part of the eye.
Answer:
The coloured part of the eye is called iris.

Question 6.
What is the function of iris ?
Answer:
It acts as a shutter or a diaphragm, controlling the size of pupil.

Question 7.
What part of eye contains several nerve cells?
Answer:
Retina contains several nerve cells.

Question 8.
Name two kinds of nerve cells found in retina.
Answer:
The two kinds of nerve cells are cones and rods.

Question 9.
What is the function of optic nerve and retina called ?
Answer:
This is called blind spot.

Question 10.
Who cart see very well in the night, but not during the day?
Answer:
Owl can see very well in the night but not during the day.

Question 11.
Which vitamin is found in green vegetables like spinach (palak)?
Answer:
Vitamin A.

Light Class 8 Extra Questions Short Answer Type 1

Question 1.
How can we see anything?
Answer:
The light when enters our eyes from an object, then we are able to see that object.

Question 2.
Define incident ray.
Answer:
The light ray, which strikes any surface, is called the incident ray.

Question 3.
Define reflected ray.
Answer:
The ray that gets bounced back from the polished surface is called the reflected ray.

Question 4.
What do you mean by laws of reflection ?
Answer:
There are two laws of reflection :
(i) The angle of incidence is equal to the angle of reflection.
(ii) The incident ray, reflected ray and the normal at the point of incidence all lie in the same plane.

Question 5.
Define plane.
Answer:
The flat surface with two-dimensional coordinates are termed as plane.

Question 6.
What do you mean by lateral inversion?
Answer:
When image is formed in a plane mirror, the left part appears as right and the right part appears as left. This phenomenon is known as lateral inversion.

Question 7.
Define regular reflection.
Answer:
The reflected rays are parallel to one another like the incident rays. This kind of reflection is called regular reflection. It takes place from a surface which is plane with no defects.

Question 8.
Define irregular or diffused reflection. How is it caused ?
Answer:
When all the reflected rays from a plane surface are not parallel like the incident rays, the reflection is known as irregular or diffused reflection.

Question 9.
Is diffused reflection due to the failure of the laws of reflection ? How is it caused ?
Answer:
No, the diffused reflection is not due to the failure of the laws of reflection. It is caused by irregularities in the reflecting surface.

Question 10.
Do we see objects due to reflected light ?
Answer:
Yes, everything except luminous object, we see around is seen due to reflected light. Moon, for example, receives light from the sun and reflects it. That is why we see the moon.

Question 11.
What is meant by luminous and illuminated objects ?
Answer:
The objects which have their own light, are called luminous objects, such as sun, fire, flame of candle, electric lamps, etc. The objects which reflect the light of other objects, are known as illuminated objects, such as moon.

Question 12.
Where are the periscopes used?
Answer:
The periscopes are used in submarines, tanks and by soldiers in bunkers to see things outside indirectly.

Question 13.
What happens if two plane mirrors in combination are used ?
Answer:
With a plane mirror, only one image of an object can be formed. But, if two mirrors in combination are used, then more than one image are formed.

Question 14.
What do you mean by dispersion of light? What is rainbow?
Answer:
The splitting of light by prism into seven constituent colours is known as dispersion of light. Rainbow is a natural example of dispersion of light.

Question 15.
What are two types of nerve cells ?
Answer:
There are two kinds of nerve cells:
(i) cones which are sensitive to bright light; and
(ii) rods which are sensitive to dim light. Cones send messages of colours also.

Question 16.
State the functions of eyelids.
Answer:
Eyelids protect eyes from any objects entering into the eye. Eyelids also shut when light is not required.

Question 17.
Describe the eyes of owls.
Answer:
The owl has a large cornea and a large pupil that allow more light in its eyes. Also, it has on its retina mostly rods and only a few cones.

Question 18.
What do you know about the cones and rods in the eyes of day birds?
Answer:
The day birds have more cones and a fewer rods, because cones are more sensitive to bright light and rods to dim light.

Question 19.
What is Braille?
Answer:
The most popular resource for visually challenged persons is Braille.

Light Class 8 Extra Questions Short Answer Type 2

Question 1.
What is kaleidoscope? What are its uses?
Answer:
The idea of number of images formed by mirrors placed at an angle to one another is used in an optical appliance called kaleidoscope. It is used to form numerous beautiful patterns. Designers of wall papers and fabric artists use kaleidoscope to get ideas for new patterns.

Question 2.
Describe the structure of eye.
Answer:
The eyes are one of the most important sense organs of human beings. Each eye has a roughly spherical shape. Outer tough coat of the eye is white that protects the interior of the eye from any damage. Its transparent front part is called cornea.

Behind the cornea, there is a small opening called the pupil. The size of the pupil is controlled by the iris which is the coloured part of the eye. This iris acts as a shutter or a diaphragm to control the amount of light entering into the eye. Behind the pupil is a lens which focuses light at the retina; placed at the back of eye.

Question 3.
What are the defects caused in eyes due to improper diet? How the defect is eradicated by taking particular type of food?
Answer:
If food is deficient in some components, eye may also suffer. Lack of vitamin A in our diet is responsible for many eye problems. Most common amongst them is night blindness.

One should, therefore, include in the diet components which have vitamin A. Raw . carrots, broccoli and green vegetables such as spinach (palak), methi, amarnath and cod liver oil are rich sources of vitamin A. Eggs, milk, curd, paneer, butter, ghee and fruits such as papaya, banana, mango, apple, dates, etc. also contain plenty of vitamin A.

Question 4.
Write a short note on persons which are visually handicapped.
Answer:
Some persons, including children, are visually handicapped. They have very limited vision to see things. Some persons cannot see at all since birth. Some persons lose their eyesight because of certain diseases.

Such persons, on their own try to identify things by touching, listening to the voices more carefully and bringing the things more closely to the eyes. In this way, they try to develop their senses more sharply. However, additional resources can further enable them to develop their capabilities.

Question 5.
Write the characteristics of image formed by a plane mirror.
Answer:
Characteristics of the image formed by plane mirror:
(a) The image formed by a plane mirror is virtual (imaginary) and erect.
(b) The image is laterally inverted. (The left side of object appear on right side of image.)
(c) The size of image is equal to that of object.
(d) The image formed is as far behind the mirror as the object is in front of it.

Question 6.
Draw a ray diagram to show the reflection produced by a plane mirror.
Answer:

Light Class 8 Extra Questions Long Answer Type

Question 1.
Describe the resources for the visually handicapped persons.
Answer:
Resources can be of two types :
(i) Non-optical aids, and
(ii) Optical aids.

(i) Non-optical aids include visual aids, tactual aids (using the sense of touch), auditory aids (using the sense of hearing) and electronic aids. With the help of visual aids, required size of words, suitable intensity of light and material at proper distances can be provided.

Tactual aids including Braille writer slate and stylus help the visually challenged persons in taking notes, reading and writing and in learning mathematics.

Auditory aids include cassette, tape recorders, talking books and other such programmes. Electronic aid such as talking calculators are also available for performing many computations. Closed-circuit television, also an electronic aid, enlarges printed materials with suitable contrasts and illumination.

Now-a-days, use of audio CDs and voice boxes with computers are also very helpful for listening and writing the desired text.

(ii) Optical aids include bifocal lenses, contact lenses, tinted lenses, other lens combinations, magnifiers and telescopic aids. While the lenses and their combinations are used to rectify visual limitations, telescopic aids are available to view chalk-boards and class demonstrations.

Question 2.
Describe in detail the Braille system of writing.
Answer:
Braille system has 63 dot patterns or characters. Each character represents a letter, combination of letters, common word or grammatical signs. Dots are arranged in cells of two vertical rows of three dots each. To identify the dpt patterns, dot positions are numbered 1, 2, 3 downwards on the left and 4, 5, 6 downward on the right as shown below :
1 ……….. 4
2 ……….. 5
3 ……….. 6

Use of the above notations:
Pattern of dots to represent English alpha-bets and some common words is shown below:

These dots when embossed on Braille sheet, help visually usually challenged to recognize words by touching. For the purpose, the words are slightly raised.

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