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Question 1

What makes things visible?

When light from an object enters our eyes that we see object.


Question 2

What happens when light falls on a mirror?

Mirror is silvered on one side, so it does not allow the light to pass through it. It reflects almost whole of the light falling on it.


Question 3

What change in the path of light takes place when light falls on a shiny surface? What is this called?

The light come back in the same place, when light falls on a shiny surface. This is known as reflection of light.


Question 4

What is incident ray?

The light ray, which strikes any surface is called the incident ray.



The ray that gets reflected from the surface of a mirror is known as the reflected ray.


Question 6

Define angle of incidence and angle of reflection.

Angle of Incidence: the angle between the normal and the incident ray is called the angle of reflection

Angle of Reflection: the angle between the normal and the reflected ray is called the angle of reflection

Question 7

Define "mirror"


A smooth shining surface, which rebounds the light back in same or in different direction is called a mirror.


Question 8

Why do we need a shiny surface for reflection?

The extent of reflection depends upon the shine and smoothness of the surface. More is the shine and smoothness of the surface, more will be the reflection. That is why, mirrors reflect most of the light falling on it. Hence, for reflection, shiny surfaces are required.


Question 9

What is reflection?

When a ray of light falls on a smooth and shiny surface, the whole of light is sent back in the same direction. It is called reflection. Mirrors do not allow even a small amount of light to pass through them. Mirrors show regular and complete reflection.


When all the parallel rays reflected from a plane are not parallel, the reflection is diffused or irregular. This is not violation of law of reflection, the reason for diffused reflection is due to irregularities in the reflecting surface.


Question 10

How many reflected rays can there be for a given single incident ray falling on a plane mirror?


For one incident ray there is one and only reflected ray.


Question 11

Explain the laws of reflection.

There are two laws of reflection
  • the angle of incidence is always equal to the angle of reflection
  • the incident ray, the normal at the point of incidence and the reflected ray all lie in the same plane
  • Question 12

    While standing before a plane mirror, if you more your right hand, which hand does your image move?
    if we move our right hand, our image will move left hand. It is because in a plane mirror our "left appears right" and "right appears left". This is called lateral inversion. Hence we can say that the plane mirror forms laterally inverted images.

    Question 13

    What are the characteristics of image formed by plane mirror?

    characteristics of images formed by plane mirror are:
  • plane mirror forms erect image
  • image formed is of the same size as the object
  • the distance of image from the mirror is equal to the distance of object from the mirror
  • it is virtual it can’t be obtained on a screen
  • image is laterally inverted
  • Question 14

    Define lateral inversion
    Phenomenon of changing left to right and right to left by the mirror, while forming images is called lateral inversion.

    Question 15

    Here are given capital letters of English alphabet encircle the letters which will not show lateral inversion on facing a plane mirror


    Question 16

    Is it possible to have a ray of light?


    A ray of light is an idealization. In reality, we have a narrow beam of light which is made up of several rays. For simplicity we use the term ray for a narrow beam of light.


    Question 17

    17.  Do we see all objects due to reflected light?

    Nearly everything seen around us is due to reflected light. Moon, for example, receives light from the sun and reflects it. That’s why we see the moon. These objects are called illuminated.

    There are other objects which give their own light such as sun, fire, flame of candle electric lamp and other. That’s why we see them. These are known as luminous objects.

    Question 18

    Movies that we see are separate pictures but we see a moving picture. How?


    The impression of an image does not vanish immediately from the retina. It persists there for about 1/16th of the second. So, it image flash on the eye at a rate faster than 16 per second, then the eye perceives a moving picture of the objects. The movies that we see are actually separate pictures. They are made to move across the eye usually at the rate of 24 per second (faster than 16 per second).


    Question 19

    Explain the internal structure of human eye. Also discuss the functions of various parts of the eye.

    Human eye is roughly spherical in shape. It has a white coloured tough outer coat. It protects the interior of the eye from any damage. Its transparent front part is called cornea. In the cornea, there is a small opening called the pupil. The size of the pupil is controlled by the iris. The iris is the coloured part of eye. The iris acts as a shutter or a diaphragm to control the amount of light entering into the eye. Behind the pupil is a convex lens which focuses light on the back of the eye on a layer called retina. Retina contains several nerve cells. Sensations felt by the nerve cells are then transmitted to the brain through the optic nerve.


    Question 20

    How many kinds of nerve ending are found is human eye? What are their functions?

    There are two kinds of nerve ending (i) cones which are sensitive to bright light and (ii) rods which are sensitive to dim light. Besides, cones send message of colour .where the optic nerve leaves the retina, there are no nerve endings. This is called the blind spot.


    Question 21

    What is the function of eyelids?

    The function of eyelids is to protect eyes from any objects entering the eye. Eyelids also shut out light when not required.


    Question 22

    What is the comfortable distance at which one can read with a normal eye?

    25 cm.


    Question 23

    Explain the function of the muscles attached to the lens of the eye

    In order to see near objects, muscles attached to the lens contract and the lens becomes thicker. On the other hand, muscles relax and the lens becomes thinner when distant objects are to be seen. This changing of the thickness of the eye lens is called accommodation.



    Some persons can see near objects clearly but cannot see distant objects distinctly. On the other hand, some persons cannot see near objects clearly but they can see distance objects distinctly. However, with suitable corrective lenses, these defects of the eye can be corrected.


    Question 25

    Why in odd ages the eye sight becomes foggy? How can this defect may be removed?

    Sometimes, particularly in old age, eyesight becomes foggy. It is due to the eye lens becoming milky and cloudy. When it happens, persons are said to have cataract. There is a loss of vision, sometimes extremely severe. It is possible to treat this defect. The opaque lens is removed and a new artificial lens is inserted. Modern technology has made this procedure simpler and safer.


    Question 26

    How does a night bird see the objects? What is the difference in the structures of the eyes of night bird and day light birds?

    Night bird (owl) can see very well in the night but not during the day. On the other hand, day light birds (kite, eagle) can see well during the day but not in the night. The owl has a large cornea and a large pulpit to allow more light in its eye. Also, it has on its retina mostly rods and only a few cones. As we have seen above, cones are more sensitive to bright light and rods to dim light. The day birds on the other hand, have more cones and a fever rods.


    Question 27

    Why one should include the vitamin A rich eatables in their diet? What are the main sources of vitamin A?

    Lack of vitamin A in foodstuff is responsible for many eye troubles. Most common amongst them is night blindness. One should, therefore, include in the diet components which have vitamin A. raw carrots, broccoli and green vegetable such as spinach (palak) methi, amaranth and cod liver oil are rich in 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 28

    What are the optical aids for visually challenged persons?

    There are many additional resources which enable the visually handicapped person to develop their capabilities. These resources can be of two types: non-optical aids and optical aids. 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 chalkboard and class demonstrations.


    Question 29

    How many types of non-optical aids for visually challenged persons are used?

    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 programs. Electronic aids such as talking calculators are also available for performing many computations. Closed circuit television, also an electronic aid, enlarges printed material with suitable contrast and illumination. Nowadays, use of audio CDs and voice boxes with the computers are also very helpful for listening and writing the desired text.


    Question 30

    Write an essay on "Braille system".

    The most popular resource for visually challenged persons is known as Braille. Louis Braille, himself a blind person, developed a system for visually challenged persons and published in 1821.

    The present system was adopted in 1932. There is Braille code for common languages, mathematics, and scientific notation. Indian languages such as Hindi, Sanskrit, Marathi, Gujarati, Bengali, Tamil, Telugu and Urdu, can be read using the Braille system Braille system has 63 dot patterns or characters. Each character represents a letter combination of letters, common word or grammatical sign.

    Visually challenged people learn the above system by beginning with letters and then to special characters and letter combinations. Methods depend upon recognition by touching. Each character has to be memorised. Braille texts can be produced by hand or by machine. To write Braille by hands, a slate is used consisting to two metal plates hinged together with paper in between them. A writer inserts a stylus to make dot patterns through a cell size opening on the upper plate. Type writer like devices and printing machines which use enclosed zinc plates to make coded impressions on paper, have also been developed.

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