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CBSE 7th Social Science Unit 15 Light Book Back Questions

Published on: 09/09/2019

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Questions:

Generic 3

4 x 3 = 12

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

Differentiate between a plane mirror, concave mirror and a convex mirror without touching them.

Which type of mirror can form a real image?

Give two uses each of a concave and a convex mirror

Generic 2

4 x 2 = 8

Briefly mention what makes things visible to us.

In the formation of a rainbow, what acts as tiny prisms?

Name the colours include in the composition of sunlight.

Briefly tell that how many reflected rays can be obtained from a single incident ray in respect of a plane mirror

Generic 5

2 x 5 = 10

One day, Ramesh's friend was performing their respective experiments given by their teacher. While sitting in the practical lab instead of performing experiment, Ramesh was playing with his meter scale. All the sudden, he held the scale in his hand and started moving in front of tubelight, then he observed the seven colours of white light. After sometimes, he got scolded by his lab teacher for not performing the experiment.
(a) Give the name of phenomenon that leads to the formation of band of seven colours.
(b) Name the constituent colours of white light.
(c) Mention the values shown by Ramesh here.

10.

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

Multiple Choice Question

5 x 1 = 5

11.

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

12.

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

13.

A rainbow can be seen in the sky

(a)

rainbow can be seen in the sky

(b)

when the sun is behind you

(c)

when the sun is overhead

(d)

only at the time of sunrise

14.

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

15.

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 respectively are

(a)

plane mirror and concave mirror

(b)

concave mirror and convex mirror

(c)

plane mirror and convex mirror

(d)

convex mirror and plane mirror

Fill up / 1 Marks

5 x 1 = 5

16.

A prism splits light into ............. colours.

17.

Convex lenses are ............ in the middle than at the edges whereas concave lenses are .................. in the middle than at the edges.

18.

A ............. is a curved transparent or translucent device that causes rays to either converge or diverge.

19.

The change in the direction of light by a mirror is called ................. of light.

20.

_________________lens is also known as a magnifying glass.

True or False

5 x 1 = 5

21.

A virtual image is larger than the object can be produced by a convex mirror.

(a)

True

(b)

False

22.

A concave mirror is also known as a converging mirror.

(a)

False

(b)

True

23.

The image formed in a plane mirror is behind the mirror.

(a)

False

(b)

True

24.

An object can be seen only if it emits light

(a)

True

(b)

False

25.

A convex lens always produces a real image.

(a)

True

(b)

False

Match the following

5 x 1 = 5

26.

Inverted image

27.

Diminished image

28.

Erect image

29.

Magnified image

30.

Real image

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Answers Key:

Generic 3

4 x 3 = 12

If the reflecting surface of a torch got rusted, it produces diffused light with lower intensity and the objects are not clearly visible in this diffused and lower intensity of light.

These mirrors can be differentiated by bringing our face close to each mirror turn by turn. Since, a plane mirror will produce an image of the same size as our face while a concave mirror will produce a magnified image and our face will look much bigger and on other sides, a convex mirror will produce a diminished image and our face will look much smaller like a small child.

A concave mirror can form a real image of an object.

Uses of convex mirror
(i) It is used in side mirrors of vehicles.
(ii) It is used in reflector of torch.
Uses of concave mirror
(i) It is used by doctors to examine eyes, ears, etc.
(ii) It is also used by dentists to see an enlarged image of the teeth

Generic 2

4 x 2 = 8

When a light ray falls on an object, then reflected light ray which comes from the object when falls on our eys, allows us to see things around us.

In the formation of a rainbow, the raindrops suspended in the atmosphere acts as tiny prism

As we know that sunlight consists of mixture of seven colours (i.e. VIBGYOR).

For a single incident ray, there will be only one reflected ray that can be obtained in respect of a plane mirror

Generic 5

2 x 5 = 10

(a) Dispersion of white light is the name of phenomenon which leads to the formation of band of seven colours.
(b) There are seven constituent colours of white light, they are Violet, Indigo, Blue, Green, Yellow, Orange, Red (i.e. VIBGYOR).
(c) Ramesh seems to be quite innovative with respect to the scientific methods and also very eager to learn science regarding phenomena.

10.

On decreasing the distance between the object and lens, the size of the image increases, the nature of the lens will be convex type.
If the distance between object and lens is less than the focus of the lens, then it forms a virtual image and this image cannot be obtained on a screen but formed on the same side of the object.

Multiple Choice Question

5 x 1 = 5

11.

12.