NCERT Solutions for Class 8th Science
Chapter 16 – LIGHT
(Complete Downloadable Chapter Solution PDF file is at the bottom of the page)
Q.1 Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the room. Explain.
Ans Objects cannot be seen in the dark room whereas one can see objects outside the room in light. This is because we see the object only when light which may have been emitted or reflected by the object enters our eyes.
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
Ans (a) Polished wooden table – Regular reflection as it has smooth surface.
(b) Chalk powder – Diffused reflection as it has irregular surface.
(c) Cardboard surface – Diffused reflection as it has irregular surface.
(d) Marble floor with water spread over it – Regular reflection as it has smooth surface.
(e) Mirror – Regular reflection as its surface is smooth.
(f) Piece of paper – Diffused reflection as it has minor irregularities.
Q.4 State the laws of reflection.
Ans Laws of reflection:
(i) The angle of incidence is equal to the angle of reflection.
(ii) Incident ray, reflected ray and the normal drawn at the point of incidence to the reflecting surface, lie in the same plane.
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 from his image.
(b) If you touch your ____________ ear with 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.
Choose the correct option in Questions 7 – 8
Q.7 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 labeled 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 teachers advise?
Q.12 Explain how you can take care of your eyes.
Q.13 What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray?
Q.14 How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by 40 cm?
Ans Infinite
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. 16.20. 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. 16.21).
(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?