NCERT Solutions for Class 8 Science Chapter 16 Light

This is a very important chapter. This chapter teaches about the properties of light and how it enables us to see any object. In this chapter of NCERT solutions for class 8 science students will learn about the angles of incidence, reflection and the various laws of reflection. They will also be advised on how to take care of their eyes.

We are able to see objects because of light. Light can move in space from one object to another. The light falling on the object is reflected towards our eyes, which allow us to see it. Reflection occurs when the rays that fall on an object is sent back.

Download PDF of NCERT Solutions for Class 8 Science Chapter 16

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

Solution: Light is required to see the objects in dark. The light from the objects reflects in our eyes and we are able to see the objects. If the light is present outside the room, then we can see the objects placed there. If no light is present outside the room, then we cannot see the objects.

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

Solution:

Regular reflection	Diffused reflection
It takes place on a smooth surface	It takes place from an irregular surface
It obeys the laws of reflection	It also obeys laws of reflection
In this type of reflection, the incident and reflected rays are parallel.	In this type of reflection, the 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

Solution

(a) Polished wooden table → Regular reflection

In a polished wooden surface, regular reflection takes place.

(b) Chalk powder → Diffused reflection

It is an example of a rough surface. Thus, the diffused reflection will take place from chalk powder.

(c) Cardboard surface → Diffused reflection

The cardboard has an irregular surface. So, the diffused reflection will take place.

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

Water makes the marble surface smooth. If the light falls on it regular reflection takes place.

(e) Mirror → Regular reflection

Mirror has a smooth surface. Therefore, it will give a regular reflection.

(f) Piece of paper → Diffused reflection

A piece of paper looks smooth, but the surface of the paper is also irregular if looked very closely. So, it will give diffused reflection.

Question 4: State the laws of reflection.

Solution

The laws of reflection are given as follows:

(i) The angle of reflection is always equal to the angle of incidence.

(ii) The incident ray, the reflected ray and the normal all lie on the same plane.

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.

Solution

● Place a plane mirror on the table in the upright position.

● Take a sheet of paper and cut a small hole in the centre of the paper.

● Place another sheet on the table so that it is in contact with the vertical mirror and draw a normal line on it from the mirror.

● Now, shine a torch through the small hole in the mirror so that the ray of light falls on the normal at the bottom of the mirror.

● When a ray from this hole strikes the mirror, it is reflected in a specific direction.

● The incident ray reflected ray, and normal to the mirror are all easily visible.

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.

Solution

(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 your right hand in front of a plane mirror, it will be seen in the mirror that your right ear is touched with your _left hand_.

(c) The size of the pupil becomes __large__ when you see in dim light.

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

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

(a) Always

(b) Sometimes

(c) Under special conditions

(d) Never

Solution: (a) The first law of reflection states that the angle of incidence is always equal to the angle of reflection.

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.

Solution

(b) The image formed by a plane mirror is virtual, behind the mirror and of the same size as the object.

Question 9: Describe the construction of a kaleidoscope.

Solution: It consists of a hollow tube that contains three mirrors arranged in a triangular manner with their reflecting surfaces facing each other. A transparent sheet is placed on one end of the tube, while an opaque sheet is placed on the other. The opaque sheet has an eyehole in it. The tube is filled with glass shards. When we turn a kaleidoscope, we observe a variety of designs. Multiple reflections combine to create these patterns.

Also get access to

NCERT Solutions for Class 8 Maths

Class 8 Maths Worksheets

Class 8 Maths Notes

Question 10: Draw a labelled sketch of the human eye.

Solution

Want to learn more about the human eye? This link will help you understand about working, function, structure and human eye diagram class 8.

Question 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 advice?

Solution: The laser light can damage the retina and lead to blindness as it has a very high intensity.

Question 12: Explain how you can take care of your eyes.

Solution: The following points should be followed to maintain eye health:

(a) We should not read in dim or in very bright light.

(b) Do not look directly towards the sun or towards the sunlight.

(c) Do not rub your eyes if small insects or dust particles enter your eyes. Wash it with cold water.

(d) Keep the book at least 25 cm away from your eyes while reading.

Question 13: What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray?

Solution: Angle of incidence = angle of reflection

The angle between the incident and reflected ray = 90^o

Angle of incidence=

Question 14: How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by 40 cm?

Solution: The number of images formed is uncountable or we can say an infinite number of images are formed.

Question 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.

Solution

The light ray will be reflected at a 60° angle from the second mirror.

Question 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?

Solution: Boojho cannot see his image in the mirror as the length of the mirror is short on its side. He can see the image of P and Q as they lie within the mirror, but he cannot see the image of R as it lies outside the mirror.

Question 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?

Solution

(a) Image of A is formed behind the mirror at the same distance.

(b) Paheli can see the image of A.

(c) Boojho can see the image of A.

(d) There is no movement in the image of A.

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