Lesson: Light

Question: 1

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

(a) Iris

(b) Cornea

(c) Lens

(d) Retina

Solution:

a

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:

b

Question: 3

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

d

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 eye with respect to position of bulb is shown in the figure below as A, B, C and D. In which position mirror will be visible?

(a) A

(b) B

(c) C

(d) D

Solution:

a

Question: 5

A small hole P is made in a piece of cardboard. The hole is illuminated by a torch as shown in the figure below. 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:

a

Question: 6

Two mirrors A and B are placed at right angles to each other as shown in the figure below.

A ray of light incident on mirror A at an angle of 25 ∘ MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8YrFr0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaacaaIYa GaaGynamaaCaaaleqabaGaeSigI8gaaaaa@3A5F@  falls on mirror B after reflection. The angle of reflection for the ray reflected from mirror B would be:

(a) 25° MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaacaaIYa GaaGynaiabgclaWcaa@3B12@

(b) 50° MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaacaaI1a GaaGimaiabgclaWcaa@3B10@

(c) 65° MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaacaaI2a GaaGynaiabgclaWcaa@3B16@

(d) 115° MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaacaaIXa GaaGymaiaaiwdacqGHWcaSaaa@3BCC@

Solution:

c

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:

b

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:

c

VERY SHORT ANSWER QUESTIONS (5)

Question: 1

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

Solution:

Iris

Question: 2

Boojho while waving his hand very fast in front of his eyes observes that his fingers appear blurred. What could be the reason?

Solution:

Boojho’s fingers appear blurred due to persistence of vision.

Question: 3

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

Solution:

Infinite number of times

Question: 4

The angle between incident ray and reflected ray is 60 ∘ . MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaacaaI2a GaaGimamaaCaaaleqabaGaeSigI8gaaOGaaiOlaaaa@3B48@  What is the value of angle of incidence?

Solution:

30 ∘ MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaacaaIZa GaaGimamaaCaaaleqabaGaeSigI8gaaaaa@3A89@

Question: 5

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:

The distance between the mirror and the object is 12 cm.

SHORT ANSWER QUESTIONS (6)

Question: 1

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

Solution:

When light gets dispersed, it splits into its constituent colours. Example: rainbow

Question: 2

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

Solution:

Question: 3

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

Solution:

No, as shown in the figure, the image of the child cannot be obtained on a screen.

Question: 4

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

Solution:

A large pupil and large cornea allow more light to enter into the eyes and thereby increases visibility, thus allowing the eyes to see objects even in dim light.

Question: 5

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

Solution:

Our eyes have convex lens and the image of any object is formed on the retina.

Question: 6

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

Solution:

The eye lens of a person becomes opaque if he is suffering from cataract. It can be treated by cataract surgery, where the natural lens is replaced with an artificial one.

LONG ANSWER QUESTIONS (6)

Question: 1

Boojho planned an activity to observe an object A through pipes as shown in the figure below, 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 rays in the figure.

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

Solution:

(a) Three mirrors

(b)

(c) 45 ∘ MathType@MTEF@5@5@+= feaagKart1ev2aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqr1ngB PrgifHhDYfgasaacH8srps0lbbf9q8WrFfeuY=Hhbbf9v8qqaqFr0x c9pk0xbba9q8WqFfea0=yr0RYxir=Jbba9q8aq0=yq=He9q8qqQ8fr Fve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaaeaaakeaacaaI0a GaaGynamaaCaaaleqabaGaeSigI8gaaaaa@3A8F@

(d)

(e) No, he will not be able to see the objects.

Question: 2

There is a mistake in each of the following ray diagrams given in the figure below. Make the necessary correction(s).

Solution:

After correction, the three cases should be as in the given diagram.

Question: 3

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

Solution:

Persistence of vision is the process which enables us to perceive motion in a cartoon film. The cartoon film is actually the projection of static pictures at the rate of 24 pictures per second on the screen in a specific order. Due to persistence of vision, the image of the object is retained on our retina for a very short period of time, and the constant change in pictures at a fast rate gives us the perception of movement.

Question: 4

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

Solution:

The kaleidoscope gives a number of images that are formed when an object is placed between two mirrors at an angle.  Designers and artists use kaleidoscope for deriving new patterns in wallpapers, jewellery and fabrics.

Question: 5

The figure below shows the word REST written in two ways in front of a mirror.

Show how the word would appear in the mirror.

Solution:

Question: 6

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

Solution:

1. Ciliary muscle

2. Iris

3. Lens

4. Cornea

5. Retina

6. Optic Nerve