Lesson: Light

# Question: 1

How does light travel?

## Solution:

Light travels in a straight path.

# Question: 2

Which type of mirror can form a real image?

Concave mirror.

# Question: 3

Which type of lens always forms a virtual image?

## Solution:

Concave lens always forms a virtual image.

# Question: 4

Define reflection of light.

## Solution:

The bouncing back of rays of light from a polished or smooth surface is called reflection.

# Question: 5

What is Newton’s disc?

## Solution:

When the disc is rotated fast, the colours get mixed together and the disc appears to be whitish. Such a disc is popularly known as Newton's disc.

# Question: 6

Which type of mirror is used as shaving mirror?

## Solution:

Concave mirror is used as shaving mirror.

# Question: 7

Which type of mirror is used as magnifying glass?

## Solution:

Convex mirror is used as a magnifying glass.

# Question: 1

What is a mirror? Write its different types?

## Solution:

Polished, smooth, even and bright surfaces are called mirrors. Mirror is best reflector of light. Major types of mirror are plane mirror, concave mirror and concave mirror.

# Question: 2

Write the difference between real and virtual image?

## Solution:

Real image: A real image can be obtained on screen. It is formed in front of the mirror.

Virtual image : A virtual image cannot be obtained on screen. It is formed behind the mirror.

# Question: 3

What is a lens? Write its types.

## Solution:

A lens is a piece of transparent substance having at least one curved surface. Two common types of lens are concave lens and convex lens.

# Question: 4

How does a  convex mirror help in driving?

## Solution:

Convex mirror always forms erect, virtual image and of smaller size than the objects.

A driver through a convex mirror can see the traffic behind him much easily as convex mirror always forms erect and virtual image which is of smaller size than the object.

# Question: 5

Why a paper held in sunshine at focus of a convex lens burns?

## Solution:

All rays of light falling on convex lens converge at one point on the principle axis called focus. The energy present in these rays of light meets at focus. These rays develop enough heat to burn the paper.

# Question: 6

Recognize these mirrors and name them.

## Solution:

i) Concave mirror

ii) Convex mirror

# Question: 7

Recognize these mirrors and name them.

i) Convex lens

ii) Concave lens

# Question: 1

How will you prove that white light consists of seven colours?

## Solution:

We can prove that white light is made up of seven colours by the following experiments.

Steps:

·         We take a glass prism.

·         We allow a narrow beam of sunlight passing through a small hole in a dark room.

·         We allow the beam to fall on one face of the prism.

·         We make the light coming out of the other face of the prism fall on a white sheet of paper.

Observation:

We observe the formation of seven colours on the white paper. These seven colours are formed due to splitting up of the white colour into seven colours.

# Question: 2

What is a virtual image? Give one situation where a virtual image is formed?

## Solution:

The image that cannot be obtained on a screen is called virtual image.

The image of our face formed by plane mirror cannot be obtained on screen. Hence, the image formed by plane mirror is a virtual image.

# Question: 3

What is a real image? Give one situation where a real image is formed?

## Solution:

The image which can be obtained on a screen is called real image.

In a cinema hall, we see the images of actors on screen.