Here we are providing Online Education for Some Light Class 8 Extra Questions and Answers Science Chapter 16 was designed by subject expert teachers. https://ncertmcq.com/extra-questions-for-class-8-science/
Online Education for Class 8 Science Chapter 16 Extra Questions and Answers Light
Light Class 8 Questions And Answers Pdf Question 1.
What is virtual image?
The image formed at a position behind the plane mirror is called a virtual image.
Light Chapter Of Class 8 Pdf Questions And Answers Question 2.
Can virtual images be obtained on a screen?
No, virtual image cannot be obtained on a screen.
Light Class 8 Questions And Answers Question 3.
How many images, does one mirror form?
The plane mirror can form only one image.
Light Chapter Of Class 8 Questions And Answers Question 4.
What name is given to the small opening behind the cornea?
The name of the small opening behind the cornea is pupil.
Light Chapter Class 8 Question Answer Question 5.
Name the coloured part of the eye.
The coloured part of the eye is called iris.
Extra Questions For Class 8 Science With Answers Question 6.
What is the function of iris?
It acts as a shutter or a diaphragm, controlling the size of pupil.
Class 8 Science Chapter 16 Light Question Answer Question 7.
What part of eye contains several nerve cells?
Retina contains several nerve cells.
Class 8 Science Chapter 16 Short Question Answer Question 8.
Name two kinds of nerve cells fo”und in retina.
The two kinds of nerve cells are cones and rods.
Light Question Answer Class 8 Question 9.
What is the function of optic nerve and retina called?
This is called blind spot.
Class 8 Light Questions And Answers Question 10.
Who carts see very well in the night, but not during the day?
Owl can see very well in the night but not during the day.
Light Questions And Answers Class 8 Question 11.
Which vitamin is found in green vegetables like spinach (palak)?
Class 8 Chapter Light Question Answer Question 12.
How can we see anything?
The light when enters our eyes from an object, then we are able to see that object.
Class 8 Physics Light Questions And Answers Question 13.
Define incident ray.
The light ray, which strikes any surface, is called the incident ray.
Light Class 8 Question Answer Question 14.
Define reflected ray.
The ray that gets bounced back from the polished surface is called the reflected ray.
Ncert Science Book Class 8 Extra Questions With Answers Question 15.
What do you mean by laws of reflection?
There are two laws of reflection :
- The angle of incidence is equal to the angle of reflection.
- The incident ray, reflected ray and the normal at the point of incidence all lie in the same plane.
The flat surface with two-dimensional coordinates are termed as plane.
What do you mean by lateral inversion?
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.
Define regular reflection.
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.
Define irregular or diffused reflection. How is it caused?
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.
Is diffused reflection due to the failure of the laws of reflection? How is it caused?
No, the diffused reflection is not due to the failure of the laws of reflection. It is caused by irregularities in the reflecting surface.
Do we see objects due to reflected light?
Yes, everything except luminous objects, 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.
What is meant by luminous and illuminated objects?
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.
Where are the periscopes used?
The periscopes are used in submarines, tanks and by soldiers in bunkers to see things outside indirectly.
What happens if two plane mirrors in combination are used?
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.
What do you mean by dispersion of light? What is rainbow?
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.
What are two types of nerve cells?
There are two kinds of nerve cells :
- cones which are sensitive to bright light; and
- rods which are sensitive to dim light. Cones send messages of colours also.
State the functions of eyelids.
Eyelids protect eyes from any objects entering into the eye. Eyelids also shut when light is not required.
Describe the ey.es of owls.
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.
What do you know about the cones and rods in the eyes of day birds?
The day birds have more cones and a fewer rods because cones are more sensitive to bright light and rods to dim light.
What is Braille?
The most popular resource for visually challenged persons is Braille.
What is kaleidoscope? What are its uses?
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 wallpapers and fabric artists use kaleidoscopes to get ideas for new patterns.
Describe the structure of eye.
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.
What are the defects caused in eyes due to improper diet? How the defect is eradicated by taking particular type of food?
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.
Write a short note on persons which are visually handicapped.
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.
Write the characteristics of image formed by a plane mirror.
Characteristics of the image formed by plane mirror :
- The image formed by a plane mirror is virtual (imaginary) and erect.
- The image is laterally inverted. (The left side of object appear on right side of image.)
- The size of image is equal to that of object.
- The image formed is as far behind the mirror as the object is in front of it.
Draw a ray diagram to show the reflection produced by a plane mirror.
Describe the resources for the visually handicapped persons.
Resources can be of two types :
- Non-optical aids, and
- Optical aids.
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 cassettes, 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.
Nowadays, use of audio CDs and voice boxes with computers are also very helpful for listening and writing the desired text.
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 chalkboards and class demonstrations.
Describe in detail the Braille system of writing.
Ans 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 :
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 recognise words by touching. For the purpose, the words are slightly raised.
Multiple Choice Questions (MCQs)
1. Fix a white sheet of paper on a drawing board. Take a comb and close all its openings except one in the middle by using a strip of black paper. Hold the comb perpendicular to the sheet of paper. Throw light from a torch through the opening of the comb from one side. With slight adjustment of the torch and the comb, a ray of light will be seen along with the paper on the other side of the comb. What will you observe if you place a strip of plane mirror in the path of the light ray?
(a) After striking the mirror, the ray of light is reflected in another direction.
(b) After striking the mirror, the ray of light is reflected back in the same direction.
(c) After striking the mirror, the ray of light is absorbed by the mirror.
(d ) After striking the mirror, the ray of light is absorbed by the sheet of paper.
(a) After striking the mirror, the ray of light is reflected in another direction.
2. The light ray which strikes any surface is called
(a) Reflected ray
(b) Incident ray
(d) Refracted ray.
(b) Incident ray.
3. The ray that comes back from the surface after reflection is known as
(a) Refracted ray
(b) Reflected ray
(c) Infrared ray
(d) Ultraviolet ray
(b) Reflected ray.