“What is Light?” – Intro for ‘Phenomena of Light’

If I switch off all the lights in this room and cover every window, what will happen?
We will still be here, the objects around us will still exist, but for us they will almost disappear.
Without light, the world is present—but invisible.

Light is a form of energy that enables us to see objects. In physics, we understand light as an electromagnetic wave which does not need any material medium to travel. It can travel through air, glass, water, and even through the vacuum of space. The light from the Sun, travelling at about (3 \times 10^8 , \text{m/s}), is the reason we have day and night, colours, shadows, and even life on Earth.

Light has some very interesting behaviours, or phenomena, when it meets different objects:

• It can bounce back – this is called reflection (like in a mirror).

• It can bend when it passes from one medium to another – this is refraction (like a stick appearing bent in water).

• It can spread out into colours – this is dispersion (as in a rainbow).

• It can bend around obstacles and overlap to form bright and dark patterns – this leads to diffraction and interference.

• It can even be polarized, showing its wave nature more clearly.

In this chapter on Phenomena of Light, we will study how and why these behaviours occur, and how we can use them in devices like mirrors, lenses, prisms, cameras, microscopes and telescopes. By the end, you will see that light is not just something that helps us to see—it is also a powerful tool for understanding nature and building technology.