EXERCISE

I. Tick the correct option to complete each sentence.

1. A luminous object produces 

Light/ sound/ noise/ water

Ans: light

2. We are able to see an illuminated object because it 

Scatters heat/ absobs light/ reflects light/ gives light

Ans: reflects light 

3. An object that forms a dark shadow is 

Transparent/ opaque/ translucent/ bright

Ans: opaque

4. An object that allows some ray of light to ass through it is called 

Translucent/ transparent/ opaque/ a mirror

Ans: translucent

5. A solar eclipse occurs when the 

Moon's shadow falls on the Earth/ Earth blocks the sun/ Earth's shadow falls on the moon/ sun stops giving off light

Ans: moon's shadow falls on the Earth.

II. Fill in the blanks. 

1. We cannot see things in the ______ of light

Ans: absence

2. A source of light can be ______ or man-made.

Ans: natural

3. Light is a form of _____

Ans: energy

4. A group of rays that travel together and parallel form a _______ of light

Ans: beam

5. A plane mirror reflects light in a _____ manner

Ans: regular

III. Answer the following questions in one sentence.

1. What is a light year?

Ans: Light year is the distance travelled by light in one year.

2. What makes illuminated object appear bright?

Ans: Illuminated object reflects light falling on it which makes it appear bright

3. What is a beam of light made up of?

Ans: A beam of light is made up of several parallel light rays.

4. When does a solar eclipse occur?

Ans: A solar eclipse occurs when the shadow of the moon falls on the earth. It occurs on new moon day.

5. When does a lunar eclipse occur?

Ans: A lunar eclipse occurs when the shadow of earth falls on the moon. It occurs on a full moon day.

IV. Answer the following questions in two sentences.

1. What are opaque objects? Give three examples.

Ans: Opaque objects are the objects that do not allow light to pass through it. Example: wood, stone, metals.

2. When is a shadow formed?

Ans: When an opaque object comes in the path of light, it blocks the light. Then a dark patch is formed on the other side. This dark patch is the shadow of the object.

3. What happens to a ray of light when it falls on a non-luminous object?

Ans: When a light ray falls on a non-luminous object, it absorbs the light rays and appears black.

4. Why does a rough surface not form an image?

Ans: The rough surface does not form an image, because when light falls on a rough surface, it reflects the light in an irregular manner.

V. Answer in about four to five sentences.

Explain rectilinear propagation of light with an experiment.

Ans: The light always travels in a straight line. This property of light is called rectilinear linear propagation of light. It can be proved by the following experiment.

The objects we need: A dust filled room having low light, a torch light.

When the torch light is turned on inside the room the path of the light becomes visible. Just by observing we can say that the light travels in a straight line.