Light: Is form of energy which enables us to see.
Where there is no light, there is no life because all animals depend on plants and plants depend on light from the sun.

Light passes in straight line that is why the shadow forms.
Light is considered the fastest thing in the world.
The speed of light in vacuum or in the air is 30 000 000 m/s

Refraction of light is the bending of light rays when it passes through new medium.
it consists:
Incident ray: Refracted ray:
Incident angle: Refracted angle

Critical Angle:
Is the angle which its refracted angle is 90.

the critical angle is less than the total internal reflection.

Total internal reflection:
Is the bouncing back of light internally to the more dense media.

it is less than critical angle.