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NCERT Solutions for Class 8 Science Chapter 16: Light

Chapter 16 Light
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The NCERT solutions for class 8 Science chapter 16 Light is extremely crucial for the students studying in CBSE class 8. These chapter 16 (Light) solutions are provided here to help the students to clear all their doubts and to help them in understanding the chapter in an easy and interesting way. This NCERT Solution provide you the answers to the question on the meaning of reflection, laws of reflection, types of mirrors, kaleidoscope and its construction, Dispersion of light, Concept of the rainbow and 7 colours, Parts of human eye and defects of the human eye.

 

NCERT Solutions for Class 8 Science Chapter 16 by Swiflearn are by far the best and most reliable NCERT Solutions that you can find on the internet. These NCERT Solutions for Class 8 Science Chapter 16 are designed as per the CBSE Class 8 Science Syllabus. These NCERT Solutions will surely make your learning convenient & fun. Students can also Download FREE PDF of NCERT Solutions Class 8 Chapter

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NCERT Solutions for Class 8 Science Chapter 16: Light

NCERT 8th Science Chapter 16 1

 

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

 

Solution:
We cannot see objects in the room when we are in a dark room. We can see the objects outside the room, because light is available outside the room. The rays of light enter our eyes after reflection from the objects outside the room.

 

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

 

Solution: Refer pdf.

 

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. Regular reflection will take place from a polished wooden table because the surface is smooth and polished.
b. Diffused reflection will take place because from the chalk powder because the surface is rough.
c. Diffused reflection will take place from the cardboard surface because the surface is rough.
d. Regular reflection will take place from a marble floor with water spread over it because the surface is smooth and plane.
e. Regular reflection will take place from a mirror because the surface is plane and polished.
f. Diffused reflection will take place from a piece of paper because the surface is rough.

 

4. State the laws of reflection.

 

Solution:
The law of reflection states that:
a) The angle of reflection and the angle of incidence are always equal.
b) The reflected ray, the incident ray, and the normal to the reflective surface at the point of incidence all lie in the same plane.

 

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:
Aim: To show that the incident ray, reflected ray and the normal at the point of incidence lie in the same plane. Materials Required: Plane mirror, holder, ray box, etc.
Procedure:
 Fix a sheet of white paper on the board.
 Place a plane mirror strip vertically on the paper using a stand.
 Throw light from a ray box on the mirror.
 Look at the reflected ray.
 Mark the incident ray, the normal and the reflected ray.
 Fold the paper which is beyond the edge of the board.
 You will observe that the reflected ray is not seen in the folded portion of the chart paper.
 Now bring the folded portion back to its original position.
 The reflected ray of light is again seen on the page.
Conclusion: The sheet on the board can be considered as a plane. The incident ray, the reflected ray, the normal at the point of incidence all lie in the same plane.

 

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

 

Choose the correct option in Questions 7 – 8

7. Angle of incidence is equal to the angle of reflection.
(a) Always
(b) Sometimes
(c) Under special conditions
(d) Never

 

Solution:
Option (a) is the correct answer.

 

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:
Option (b) is the correct answer.

 

9. Describe the construction of a kaleidoscope.

 

Solution:
The steps involved in the construction of a kaleidoscope are as follows:
 Take three rectangular mirror strips of dimensions 15cm × 4cm (l × b) and join them togetherto form a prism.
 Fix the prism into a circular cardboard tube.
 Make sure that the circular cardboard tube is slightly longer than the prism. Now close one
end of the circular tube with a cardboard disc.
 This disc has a hole through which we can see.
 Fix a plane glass at the other end of the circular tube.
 Take care that this glass plate touches the prism mirrors.
 Place several small and broken pieces of coloured glass are placed on this glass plate.
 Now, close this end by a round glass plate. Make sure that there is enough space for the coloured glass pieces to move.

 

10. Draw a labelled sketch of the human eye.

 

Solution: Refer pdf.

 

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:
Teacher has advised Gurmit not to use laser light because laser light has very high intensity. This may be very harmful to the eyes and can cause a permanent defect in the eye.

 

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

 

Solution:
The following points need to be followed in order to take care of the eyes:
a) One should not read in very bright light as well as dim light.
b) One should visit an eye specialist at regular intervals of time.
c) One should not rub the eyes in case any small insects or dust particles enters the eyes.
d) One should avoid direct exposure of eyes to the sunlight.
e) There should be a minimum distance of at least 25 cm between the eyes and the book while reading.

 

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:
Given, the angle of reflection is 90°.
According to the laws of reflection, angle of incidence is always equal to angle of reflection.

Here it is given that the angle between the incident ray and reflected ray is 90°. i.e.,
∠i + ∠r = 90°
Now, ∠i = ∠r
We get, ∠i + ∠i = 90° ⇒ 2∠i = 90° ⇒∠i = 45°
Angle of incidence = 45°

 

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

 

Solution:
An infinite number of images will be formed as the mirrors are placed parallel to each other.

 

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: Refer pdf.

 

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:
No, Boojho can’t see himself in the mirror. He can see the image of the object at P and Q but not of R.

 

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) The image of the object at A is formed behind the mirror.
b)Yes, Paheli can see this image.
c) Yes, Boojho can see this image.
d) When Paheli moves from B to C, the image of the object at A will not move.

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