Answer :

If the reflected ray is at the angle of 90 degrees to the incident ray, then the angle of incidence is 45 degrees.

According to the law of reflection, the angle of incidence is equal to the angle of reflection.

Therefore, the angle of incidence and the angle of reflection both are equal to

90/2 = 45 degrees.

- Q.1 Suppose you are in a dark room. Can you see objects in the room? Can you see objects out¬side the room ?
- Q.2 Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the laws of reflection?
- Q.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
- Q.4 State the laws of reflection.
- Q.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.
- Q.6 Fill in the blanks in the following. (a) A person 1 m in front of a plane mirror seems to be ______ m away from his image. (b) If you touch your ______ ear with a right hand in front of a plane mirror it will be seen in the mirror that your right ear is touched with _____ (c) The size of the pupil becomes _______ when you see in dim light. (d) Night birds have _______ cones than rods in their eyes.
- Q.7 The angle of incidence is equal to the angle of reflection (a) Always (b) Sometimes (c) Under special conditions (d) Never
- Q.8 Image formed by a plane mirror is: (a) virtual, behind the mirror and enlarged. (b) virtual, behind the mirror and of the same size as the object. (c) real at the surface of the mirror and enlarged. (d) real, behind the mirror and of the same size as the object.
- Q.9 Describe the construction of a kaleidoscope.
- Q.10 Draw a labelled sketch of the human eye.
- Q.11 Gurmit wanted to perform Activity 16.8 using a laser torch. Her teacher advised her not to do so. Can you explain the basis of the teacher’s advise?
- Q.12 Explain how you can take care of your eyes.
- Q.14 How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by 40 cm?
- Q.15 Two mirrors meet at right angles. A ray of light is incident on one at an angle of 30° as shown in Fig. 16.19. Draw the reflected ray from the second mirror.
- Q.16 Boojho stands at A just on the side of a plane mirror as shown in Fig. Can he see himself in the mirror? Also can he see the image of objects situated at P, Q and R?
- Q.17 (a) Find out the position of the image of an object situated at A in the plane mirror (Fig. 16.23). (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?

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