Ncert solutions science class 8 Solutions for Chapter 16 light

We can see a non-luminous object when light:

(a) emitted by the object falls on the eye.

(b) is reflected from the object towards our eye.

(c) completely passes through the object.

(d) gets completely absorbed by the object.

Part of the eye which controls the light entering is called

(a) iris

(b) cornea

(c) lens

(d) retina

Q1) Suppose you are in a dark room. Can you see objects in the room? Can you see objects outside the room? Explain.

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

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

Q2) Differentiate between regular and diffused reflection. Does diffused reflection mean the failure of the laws of reflection?

Q3) 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

Light is falling on surface S1, S2, S3 as shown in Fig.

Surfaces on which the angle of incidence is equal to the angle of reflection is/are

(a) S1 only

(b) S1 and S2 only

(c) S2 and S3

(d) all the three surfaces

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

A tiny mirror M is fixed on a piece of cardboard placed on a table. The cardboard is illuminated by light from a bulb. The position of the eye with respect to the position of the bulb is shown in Fig. as A, B, C, and D. In which position mirror will be visible?

a. A

b. B

c. C

d. D

Q4) State the laws of reflection.

State the laws of reflection.

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.

Q5)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.

Two mirrors A and B are placed at right angles to each other as shown in Fig.’

A ray of light incident on mirror A at an angle of 250 falls on mirror B after reflection. The angle of reflection for the ray reflected from mirror B would be

(a) 250

(b) 500

(c) 650

(d) 1150

Q6) (a) A person 1m 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.

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.

Q7) Choose the correct option: Angle of incidence is equal to the angle of reflection

(a) Always (b) Sometimes

(c) Under special conditions (d) Never

The angle of incidence is equal to the angle of reflection.

(a) Always

(b) Sometimes

(c) Under special conditions

(d) Never

Which of the following statements is correct regarding rods and cones in the human eye?

(a) Cones are sensitive to dim light.

(b) Cones are sensitive to bright light.

(c) Rods are sensitive to bright light.

(d) Rods can sense colour.

Q8) Choose the correct option: 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.

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.

In the figure of the human eye (Fig.), the cornea is represented by the letter

(a) A

(b) B

(c) C

(d) D

Describe the construction of a kaleidoscope.

Q9) Describe the construction of a kaleidoscope.

Name the part of the eye which gives colour to the eyes

Q10) Draw a labeled sketch of the human eye.

Boojho while waving his hand very fast in front of his eyes, observes that his fingers appear blurred.

What could be the reason for it?

Draw a labelled sketch of the human eye.

Q11) 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?

How many times is a ray of light reflected by two plane mirrors placed parallel and facing each other?

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?

Q12) Explain how you can take care of your eyes.

Explain how you can take care of your eyes.

The angle between incident ray and reflected ray is 60°. What is the value of angle of incidence?

The distance between the object and its image formed by a plane mirror appears to be 24 cm. What is the distance between the mirror and the object?

Q13) What is the angle of incidence of a ray if the reflected ray is at an angle of 90° to the incident ray?

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

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

Q14) How many images of a candle will be formed if it is placed between two parallel plane mirrors separated by 40 cm?

What happens to light when it gets dispersed? Give an example.

Q15) Two mirrors meet at right angles. A ray of light is an incident on one at an angle of 30° as

Draw the reflected ray from the second mirror.

Draw Fig. showing the position of the plane mirror. Also label the angle of incidence and angle of reflection on it.

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.

Q16) 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?

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?

Look at Fig. Can the image of the child in it be obtained on a screen?

Q17) (a) Find out the position of the image of an object situated at A in the plane mirror Fig.

(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?

Eyes of the nocturnal birds have large cornea and a large pupil. How does this structure help them?

(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?

What kind of lens is there in our eyes? Where does it form the image of an object?

Which part of the eye gets affected if someone is suffering from cataract? How is it treated?

Boojho planned an activity to observe an object A through pipes as shown in Fig. , so that he could see objects which he could not directly see.

(a) How many mirrors should he use to see the objects?

(b) Indicate the positions of the mirrors in the figure.

(c) What must be the angle with respect to the incident light at which he should place the mirrors?

(d) Indicate the direction of the rays in the figure.

(e) If any of the mirrors are removed, will he be able to see the objects?

There is a mistake in each of the following ray diagrams given as Fig. a, b, and c. Make the necessary correction (s).

Explain the process which enables us to perceive motion in a cartoon film.

How is the phenomenon of reflection used in making a kaleidoscope? What are the applications of a kaleidoscope?

Fig. shows the word REST written in two ways in front of a mirror. Show how the word would appear in the mirror.

Write down the names of parts of the eye in the blank spaces shown in Fig.