Light - Class 7 CBSE Notes

What is Light?

1. It is a form of energy that enables us to see.
2. Light always travels in a straight line.
3. It travels in the form of electromagnetic waves.
4. Light has the maximum speed in this world (3x10⁸ m/s -in vacuum).

Sources of Light

➥ Light sources can be classified into two main types:

1. Natural Sources: Objects that generate their own light, such as the Sun, stars, fireflies, etc.
2. Human-made Sources: Sources created by humans, such as electric bulbs, torches, lamps, candles, etc.

Reflection of Light

➥ When light strikes a smooth surface, it bounces back. This is known as reflection.

Law of Reflection: The angle of incidence is equal to the angle of reflection. Both are measured with respect to the normal (a line perpendicular to the surface at the point of incidence).

Spherical Mirrors

➥ Spherical mirrors are of two types:

• Concave Mirrors: These mirrors are curved inward. They converge light rays that fall on them.
• Convex Mirrors: These mirrors are curved outward. They diverge light rays that fall on them.

Concave and Convex Mirrors

Concave and convex mirrors are used in various applications:

• Concave Mirrors: Used in telescopes, microscopes, and shaving mirrors for focusing light.
• Convex Mirrors: Used in rearview mirrors of vehicles and in security mirrors for wide-angle viewing.

Uses of Light

Light has many uses in our daily lives:

• Helps us see objects and navigate in the dark.
• Enables the process of photosynthesis in plants.
• Used in optical instruments like microscopes and telescopes.
• Used in communication devices like fiber-optic cables.
• Plays a role in the formation of rainbows through refraction and dispersion.

Converging and Diverging Light

Converging light: Light rays that come together at a single point after reflection or refraction. It occurs in concave mirrors or converging lenses.

Diverging light: Light rays that spread out after reflection or refraction. It occurs in convex mirrors or diverging lenses.

Prism and Formation of Rainbow

A prism is a transparent optical object that refracts light. When white light passes through a prism, it splits into its component colors due to dispersion of light.

The seven colors of the spectrum are: Violet, Indigo, Blue, Green, Yellow, Orange, Red. This is known as the formation of a rainbow.

Important: The phenomenon of dispersion explains why a rainbow appears after a rainstorm, as water droplets in the air act as tiny prisms.