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Question 1

Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the room? Explain.

We can see an object only if light from an object enters our eyes. The light may be emitted by the object or may have been reflected by the object. Thus we cannot see an object which is placed in a dark room if it does not emit light of its own. Whereas an object outside the dark room can be seen if there is either light outside the dark room on the object emits its own light

Question 2

Differentiate between regular and diffuse reflection. Does diffuse reflection mean the failure of the laws of reflection?

Regular reflection Diffuse reflection
1. occurs from shiny and smooth surfaces

2. reflected rays are parallel to each other

1. occurs from unpolished and rough surface

2. reflected rays are not parallel to each other

Question 3

Mention against each of the following whether regular or diffused reflection will take place when a beam of light strikes. Justify your answer in each case

a) polished wooden table b) chalk powder c) cardboard surface d) marble floor with water spread over it e) mirror f) piece of paper

a. polished wooden table: regular reflection will takes place. This is because polished wooden table will have a plane surface

b. Chalk powder: diffused reflection because the surface of the chalk powder will be uneven

c. cardboard surface: diffused reflection since cardboard has a rough surface

d. marble floor with water spread over it: regular reflection as it will act like a plane surface

e. mirror: regular reflection because mirror has a shiny surface which is even

f. piece of paper: diffused reflection. Since surface of a paper is uneven

Question 4

State the laws of reflection.


There are two laws which govern reflection
  •  the incident ray, the normal at the point of incidence and the reflected ray are in the same plane
  • the angle of reflection is equal to the angle of incidence
  • Question 5

    Describe an activity to show that the incident ray, the reflected ray and the normal at the point of incidence lie in the same plane.
    First of all we take a chart paper or stiff paper. Let the sheet project a little beyond the edge of the table.

    Perform activity again. This time use a sheet of stiff paper or a chart paper. Let the sheet project a little beyond the edge of the table cut the projecting portion of the sheet in the middle. Look at the reflected ray. Make sure that the reflected ray extends to the projected portion of the paper. Bend that part of the projected portion on which the reflected ray falls. Bring the paper back to the original position. When the whole sheet of paper is spread on the table, it represents one plane.

    The incident ray, the normal at the point of incidence and the reflected ray are all in this plane when you bend the paper you create a plane different from the plane in which the incident ray and the normal lie. Then you do not see the reflected ray. It indicates that the incident ray, the normal at the point of incidence and the reflected ray all life in the same plane. This is another law of reflection.

    Question 6

    Describe the construction of a kaleidoscope.


    In kaleidoscope, the idea of formation of number of images by mirrors placed at an angle to one another is used to make numerous beautiful patterns

    Question 7

    Draw a labeled sketch of the human eye


    Question 8

    Gurmit wanted to perform activity using a laser torch. Her teacher advised her not to do so. Can you explain the basis of the teachers advise?


    Laser is a highly energetic beam of light and it can be a harm to the eyes. This the reason for Gurmit’s teacher to advise him not to do perform the activity.

    Question 9

    Explain how your can take care of your eyes.

    It is necessary that we take proper care of our eyes. If there is any problem we should go to an eye specialist. Have a regular checkup. We must:
  • If advised use suitable spectacles
  • Too little or too much light is bad for the eyes. Insufficient light causes eyestrain and headaches. Too much light like that of the sun, or powerful lamps, can injure retina, which is very delicate
  • Do not look at the sun or a powerful light directly
  • Never rub our eyes if any small particle or dust goes into our eyes. Wash our eyes with clean water. If condition does not improve go to a doctor.
  • Wash our eyes frequently with clean water
  • Always read at the normal distance for vision
  • Question 10

    What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray?

    Given that,

    We know that,

    Replacing ∠ r in equation (1) with ∠ i




    Question 11

    How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by 40cm?


    Infinite number of images.

    Question 12

    Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° as shown in figure. Draw the reflected ray from the second mirror


    Question 13

    Boojho stands at A just on the side of a plane mirror as shown in figure. Can he see himself in the mirror? Also can he see the image of objects situated at P, Q and R?


    No, he can see image of object at P but not of Q and R

    Question 14

    a. Find out the position of the image of an object situated at A in the plane mirror as shown in the figure given below.


    b. Can Paheli at B see this image?

    c. Can Boojho at C see this image?

    d. When Paheli moves from B to C, where does the image of A move?

    a. A1

    b. yes

    c. yes

    d. no change as position of A is not changing

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