NCERT Exemplar Solutions Class 8 Science Light

Multiple Choice Questions.....................

Question 1: Part of the eye which controls the light entering is called

(a) iris

(b) cornea

(c) lens

(d) retina 

Solution 1:  (a) iris 

Behind the cornea is the iris, a dark muscular organ. Its purpose is to regulate the amount of light that enters the room.

Question 2: 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. 

Solution 2: (b) is reflected from the object towards our eye.

We can see a non-luminous object when light is reflected from the object towar\ ds our eye.

Question 3:  Light is falling on surface S1, S2, S3 as shown in figure below.

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 

Solution 3: (d) all the three surfaces

Since the laws of reflection are always applied regardless of the object's surface, the angle of incidence equals the angle of reflection.

Question 4:  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 given figure as A, B, C and D. In which position mirror will be visible?

(a) A

(b) B

(c) C

(d) D 

Solution 4:  (a) A 

When a beam of light from A hits a mirror, it is mirrored back, resulting in an equal angle of incidence and reflection.

Question 5:  A small hole P is made in a piece of cardboard. The hole is illuminated by a torch as shown in below figure. The pencil of light coming out of the hole falls on a mirror.

At which point should the eye be placed so that the hole can be seen?

(a) A

(b) B

(c) C

(d) D 

Solution 5:  (a) A

Since the hole can only be seen when the angle of incidence equals the angle of reflection, the eye should be positioned at location A.

Question 6:  Two mirrors A and B are placed at right angles to each other as shown in Fig.16.4.

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 

Solution 6:  (c) 65⁰

Since the reflected ray from mirror A forms an incident ray on mirror B and is then reflected back at an angle of 65°, the angle of reflection for the ray reflected from mirror B will be 65°.

Question 7:  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. 

Solution 7:  (b) Cones are sensitive to bright light.

Cones detect colour because they are sensitive to bright light, while rods are sensitive to dim light and cannot detect colour.

Question 8: In the figure of the human eye the cornea is represented by the letter

(a) A

(b) B

(c) C

(d) D 

Solution 8:  (c) C

Very Short Answer Questions......................

Question 9: Name the part of the eye which gives colour to the eyes 

Solution 9: The iris is the part of the eye that gives the eyes their colour.

Question 10:  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? 

Solution 10:  Boojho's blurred vision is due to persistence of vision, when he finds when moving his hand very rapidly in front of his eyes that his fingers look blurred.

Question 11: How many times is a ray of light reflected by two plane mirrors placed parallel and facing each other? 

Solution 11:  A ray of light reflected by two plane mirrors positioned parallel and facing each other an infinite number of times.

Question 12:  The angle between the incident ray and the reflected ray is 60°. What is the value of the angle of incidence? 

Solution 12:   The angle between the incident ray and the reflected ray is 60°. The value of the angle of incidence is 30°.

Question 13:  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? 

Solution 13:   The distance between the object and its image formed by a plane mirror appears to be 24 cm. The distance between the mirror and the object will be 12 cm.

Short Answer Questions......................

Question 14. What happens to light when it gets dispersed? Give an example. 

Solution 14:  When light is scattered, it is broken down into its component colours. Consider the rainbow.

Question 15:  Draw figure showing the position of the plane mirror. Also, label the angle of incidence and angle of reflection on it.

Solution 15:

Question 16:  Look at the figure given below. Can the image of the child in it be obtained on a screen?

Solution 16:  No, since the image of the child is a virtual image, it cannot be obtained on a computer.

Question 17:  Eyes of the nocturnal birds have large cornea and a large pupil. How does this structure help them?

Solution 17:  And in low light, they can see things. Since they have a large pupil and a large cornea, more light will reach their eyes.

Question 18: What kind of lens is there in our eyes? Where does it form the image of an object? 

Solution 18:  The picture is created on the retina by a convex lens in our eyes.

Question 19: Which part of the eye gets affected if someone is suffering from cataract? How is it treated? 

Solution 19:  The cloudiness of a person's eye lens indicates that they have a cataract. Cataracts may be handled by using an artificial lens to replace the opaque lens.

Long Answer Questions......................

Question 20:  Boojho planned activity to observe an object A through pipes as shown given figure, 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? 

Solution 20:

(a) To see the things, he should use three mirrors.

Question 21:  There is a mistake in each of the following ray diagrams given in figure a, b, and c. Make the necessary correction (s).

Solution 21:

Question 22:  Explain the process whic h enables us to perceive motion in a cartoon film. 

Solution 22:   A carton movie is simply a static image projected on a wall. The illusion of movement is generated by showing 24 pictures per second in a particular order.

Question 23:  How is the phenomenon of reflection used in making a kaleidoscope? What are the applications of a kaleidoscope? 

Solution 23:   The kaleidoscope creates a variety of images by reflecting light from mirrors that are angled in different directions. Designers and artists use the kaleidoscope to come up with new designs for wallpaper, jewellery, and fabrics.

Question 24:  Below given figure shows the word REST written in two ways in front of a mirror. Show how the word would appear in the mirror.

Solution 24:

Question 25:  Write down the names of parts of the eye in the blank spaces shown in figure given below.

Solution 25:

1. Ciliary muscle

2. Iris

3. Lens

4. Cornea

5. Retina

6. Optic Nerve