Light and Sound

Concept: Sources and Properties of Light

What is light?

Light is a form of energy, and it travels as light rays in the form of straight lines. Light can travel through vacuum, which is why the Earth receives light from the Sun. Light rays also interact with different types of objects and materials.

Luminous and non-luminous objects:

Based on the ability to emit light, objects can be classified as luminous and non-luminous objects.

Luminous objects: The objects which can emit light are called luminous objects.
Example: , candle, bulb.

Non-luminous objects: The objects which cannot emit light are called non-luminous objects.
Example: Bricks, wood, coal, metallic objects.

Sources of light:

All luminous sources of light can be classified into two groups—

• Natural sources: These sources have the ability to emit light on their own.



Example:






Sun






Stars






Lightening

• Artificial sources: These sources generate light artificially.



Example:






Light Blub






Torch






Candle

Transparent, translucent and opaque objects:

Different types of objects interact with light differently based on the material with which the object is made. Some objects do not allow the passage of light through them, while others allow light to pass through. Objects can be classified into three categories based on their interaction with light—

Opaque objects: These objects do not allow light to pass through them. The light gets either absorbed or reflected from the object.
Example: Chair, table, metal box, etc.

Translucent objects: These objects allow only some amount of light to pass through them. So, all the things appear blurry when one sees through a translucent object.
Example: Frosted glass, butter paper, wax paper, etc.

Transparent objects: These objects allow light rays to pass through them, and we can clearly see what is there on the other side of those objects.
Example: Glass bottle, glass window pane, etc.

Properties of light:

• Light rays travel in all directions from their source.

• Light rays always travel in straight lines as long as nothing blocks their way.


• Light moves at the fastest known speed in the universe.
• Light has the ability to pass through vacuum.
• Light is absorbed by certain objects and finally gets converted into heat energy.

• Light gets reflected, i.e., it bounces off from the surface of an object.

• Light gets refracted, i.e., the directions of light rays change when they pass from one medium to another, like from air to water.

New Words:

Did You Know?

• Dark colours absorb light, helping us stay warmer in the winter. However, in the summers, light colours absorb less of the Sun's heat, thereby keeping us cooler.
• White light is actually a mixture of all colours, namely red, orange, yellow, green, blue, indigo, and violet.





• The study of the nature and properties of light is called optics.