Lesson: Light

# Question:1

Boojho and Paheli were given one mirror each by their teacher. Boojho found his image to be erect and of the same size whereas Paheli found her image erect and smaller in size. This means that the mirrors of Boojho and Paheli are, respectively

(a)   Plane mirror and concave mirror

(b)   Concave mirror and convex mirror.

(c)   Plane mirror and convex mirror.

(d)   Convex mirror and plane mirror.

c

# Question:2

Which of the following can be used to form a real image?

(a)   Concave mirror only.

(b)   Plane mirror only.

(c)   Convex mirror only.

(d)   Both concave and convex mirrors.

a

# Question:3

If an object is placed at a distance of 0.5 m in front of a plane mirror, the distance between the object and the image formed by the mirror will be

(a)   2 m

(b)   1 m

(c)   0.5 m

(d)   0.25 m

b

# Question: 4

You are provided with a concave mirror, a convex mirror, a concave lens and a convex lens. To obtain an enlarged image of an object you can use either

(a)   Concave mirror or convex mirror.

(b)   Concave mirror or convex lens.

(c)   Concave mirror or concave lens.

(d)   Concave lens or convex lens.

b

# Question: 5

A rainbow can be seen in the sky

(a)   When the sun is in front of you.

(b)   When the sun is behind you.

(c)   When the sun is overhead.

(d)   Only at the time of sun rise

b

# Question: 6

An erect and enlarged image can be formed by

(a)   Only a convex mirror.

(b)   Only a concave mirror.

(c)   Only a plane mirror.

(d)   Both convex and concave mirrors.

b

# Question: 7

You are provided with a convex mirror, a concave mirror, a convex lens and a concave lens. You can get an inverted image from

(a)   Both concave lens and convex lens.

(b)   Both concave mirror and convex mirror.

(c)   Both concave mirror and convex lens.

(d)   Both convex mirror and concave lens.

c

# Question: 8

An image formed by a lens is erect. Such an image could be formed by a

(a)   Convex lens provided the image is smaller than object.

(b)   Concave lens provided the image is smaller than object.

(c)   Concave lens provided the image is larger than object.

(d)   Concave lens provided the image is of the same size.

b

# Question: 9

The image formed by a lens is always virtual, erect and smaller in size for an object kept at different positions in front of it. Identify the nature of the lens.

Concave lens.

# Question: 10

Fill in the blanks:

(a)            The inner surface of a steel spoon acts as a _________mirror.

(b)            The outer surface of a flat steel plate acts as a _________mirror.

(c)            The outer shining surface of a round bottom steel bowl acts as a ________ mirror.

(d)            The inner surface of the reflector of a torch acts as a________ mirror

(a) Concave

(b) Plane

(c) Convex

(d) Concave

# Question: 11

State whether the following statements are True or False.

(a)               A concave lens can be used to produce an enlarged and erect image.

(b)                A convex lens always produces a real image.

(c)               The sides of an object and its image formed by a concave mirror are always interchanged.

(d)               An object can be seen only if it emits light.

(a) False

(b) False

(c) True

(d) False

# Question: 12

What type of mirror is used as a side mirror in a scooter? Why is this type of mirror chosen?

## Solution:

Convex mirror always forms erect, virtual image and of smaller size than the objects. This helps the driver to see the traffic behind much easily having a wider view field.

# Question: 13

Observe the figures given carefully. The given figures show the path of light through lenses of two different types, represented by rectangular boxes A and B. What is the nature of lenses A and B? ## Solution:

A is a convex lens;

B is concave lens.

# Question: 14

Boojho made light from a laser torch to fall on a prism. Will he be able to observe a band of seven colours? Explain with a reason.

## Solution:

No, he will not be able to observe a band of seven colours as a laser torch gives out light of only one colour.

# Question: 15

State the correct sequence (1-7) of colours in the spectrum formed by the prisms A and B, shown in figure below. ## Solution: # Question: 16

The side mirror of a scooter got broken. The mechanic replaced it with a plane mirror. Mention any inconvenience that the driver of the scooter will face while using it?

## Solution:

In case of plane mirror, the driver will have limited view of the traffic behind him as the mirror will not be able to cover traffic spread over a large area behind him.

# Question: 17

The concave reflecting surface of a torch got rusted. What effect would this have on the beam of light from the torch?

## Solution:

The intensity of the rays will be low and hence visibility would be poor.

# Question: 18

An erect and enlarged image of an object is formed on a screen. Explain how this could be possible.

## Solution:

If the object is placed upside down between F and 2F of the lens, then an erect and enlarged image of the object will be formed on a screen.

# Question: 19

Two different types of lenses are placed on a sheet of newspaper. How will you identify them without touching?

## Solution:

When we look through the convex lens, we will find the letters appear bigger/ magnified.  On the other hand, if the letters appear smaller, then the lens will be concave lens. So, based on how the letters appear, we will be able to identify the lenses.

# Question: 20

A shopkeeper wanted to fix a mirror which will give a maximum view of his shop. What type of mirror should he use? Give reason.

## Solution:

The shopkeeper should use convex mirror. A convex mirror forms images of object which is spread over a large area.

# Question: 21

The distance between an object and a convex lens is changing. It is noticed that the size of the image formed on a screen is decreasing. Is the object moving in a direction towards the lens or away from it?

## Solution:

In this case, the object is moving away from the lens as in case of a convex lens as the object distance increases the size of the image formed on the screen decreases.

# Question: 22

Suppose we wish to obtain the real image of a distant tree.  Explain two possible ways in which we can do it.

## Solution:

To obtain the real image of a distant tree, we can use the following two options:

a)      Concave mirror and a screen

b)      Convex lens and a screen

Concave mirror and convex lens form real image of distant objects.

# Question: 23

It was observed that when the distance between an object and a lens decreases, the size of the image increases. What is the nature of this lens? If you keep on decreasing the distance between the object and the lens, will you still able to obtain the image on the screen? Explain.

## Solution:

It is a convex lens.

The image of an object formed is virtual when the object is placed close to a convex lens. It means we will not be able to obtain the image on the screen.

# Question: 24

You are given three mirrors of different types. How will you identify each one of them?

## Solution:

We can identify the three mirrors by the image they are able to form.

A plane mirror forms erect and virtual image which is of the same size as the object.

A concave mirror can form a real and inverted image.

However, when the object is placed very close to the mirror, then it forms virtual, erect and magnified image.

A convex mirror forms an erect, virtual and diminished image of an object.