NCERT Solutions for Class 8 Science Chapter 16 Light

Question:- 1. Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the room. Explain.

Answer:- When we’re in a dark room, we can’t see object around us. We can see the the objects outside the room because light is available outside the room and rays of light can reach our eyes after being reflected by the objects.

Question:- 2. Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the laws of reflection?

Answer:-

Regular Reflection	Diffused Reflection
All the reflected rays are parallel.	The reflected rays are not parallel.
It occurs when the surface is smooth and polished.	It occurs when the surface is rough.
Rays reflected in one direction.	Rays scattered in different directions.
Example: Reflection by a plane mirror.	Example: Reflection by any rough surface

No, diffused reflection does not mean the failure of laws of reflection.

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

Answer:-

(a) Polished wooden table :- Regular reflection

(b) Chalk powder :- Diffused reflection

(d) Marble floor with water spread over it :- Regular reflection

(e) Mirror :- Regular reflection

(f) Piece of paper :- Diffused reflection

Question:- 4. State the laws of reflection.

Answer:- The laws of reflections states that:-

The incident ray, the normal and the reflected ray, all lie in the same plane.
The angle of incidence is always equal to the angle of reflection

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.

Answer:- On a table, place a plane mirror perpendicularly. Now take a paper and make a small hole in it and hold it perpendicularly too. Place another piece of paper on the table so that it comes into touch with the mirror. On the piece of paper on the table, draw a line perpendicular to the mirror. Now, using a flashlight, throw light rays through the little hole such that the beam strikes the normal at the bottom of the mirror. The ray of light from the hole will be reflected in the light rays incident on the mirror. We can clearly see that the incident ray, the normal line, and the reflected ray at the point of incidence all lie in the same plane by looking at the piece of paper on the table.

Question:- 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 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.

Answer:-

(a) A person 1 m in front of a plane mirror seems to be 2 m away from his image.

(b) If you touch your left ear with right hand in front of a plane mirror it will be seen in the mirror that your right ear is touched with left hand.

(d) Night birds have fewer cones than rods in their eyes.

Choose the correct option in Questions 7 – 8

Question:- 7. Angle of incidence is equal to the angle of reflection.

(a) Always (b) Sometimes

(c) Under special conditions (d) Never

Answer:- (a) Always

Question:- 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.

Answer:- (b) virtual, behind the mirror and of the same size as the object.

Question:- 9. Describe the construction of a kaleidoscope.

Answer:- A kaleidoscope is a device that works on the multiple reflections principle. It is made up of three long and narrow strips of plane mirrors that are angled at a 60° angle to one another to form a prism. This is enclosed within a tube. A cardboard disc with a hole in the centre closes one end of the tube. A plane glass plate is fixed to the opposite end of the mirrors, on which shattered pieces of coloured bangles are inserted. A ground glass plate closes this end of the tube.