Why do we see different colours in a rainbow?

In one line

The rule

A rainbow forms when sunlight is bent (refracted), reflected inside raindrops, and split (dispersed) into its different colours.

Let's understand it simply

Imagine you are playing cricket just after a rain. The sun comes out, and you see a beautiful rainbow in the sky. Why do you see so many colours? It is because sunlight, which looks white, is actually made up of many colours mixed together. When sunlight enters a raindrop, it bends and spreads out, just like when you shine a torch through a glass of water and see colours on the wall. Each colour bends by a different amount, so they spread out and form a rainbow.

How it works

1. Sunlight (white light) hits a raindrop in the sky.
2. The light bends (refracts) as it enters the raindrop because water slows it down.
3. Inside the drop, the light reflects off the back of the drop, like a ball bouncing off a wall.
4. As the light comes out of the drop, it bends again.
5. Each colour bends by a different amount: red bends the least, violet bends the most.
6. The colours spread out and reach your eyes at different angles, so you see a band of colours.

The story behind it

The first person to explain why rainbows have different colours was Isaac Newton, a famous English scientist in the 1600s. He used a glass prism (a see-through triangle) to show that sunlight splits into many colours. Newton called this process "dispersion". Before him, people thought rainbows were magical or messages from the gods. Newton showed it was all about how light behaves.

Where you see it in real life

• After rain, when the sun shines and there are still raindrops in the air → you see a rainbow in the sky because sunlight splits in the drops.
• Spraying water with a pipe in your garden on a sunny day → tiny water drops act like raindrops and make mini rainbows.
• Looking at oil spills on wet roads → thin oil layers split light, showing rainbow-like colours.
• Soap bubbles → the thin layer splits light, making colourful patterns.
• Glass prism in a lab or classroom → sunlight splits into a rainbow of colours.
• CDs and DVDs → the surface splits light into colours, making rainbow patterns.

Why it matters

• It helps us understand how light works, which is important in science and technology.
• The same rule is used in making lenses for glasses and cameras.
• It explains why the sky is blue and sunsets are red (because of how light bends and spreads).
• Knowing about light splitting helps in making raincoats, sunglasses, and even in studying stars and planets.

Worked example

Let's see how a raindrop splits sunlight:

Given: Sunlight (white light) enters a raindrop
Step 1: Light bends (refracts) as it enters the drop
Step 2: Light reflects inside the drop
Step 3: Light bends again as it leaves the drop
Step 4: Red light bends about 42°, violet about 40°
Step 5: The spread of angles makes the rainbow's colours

Common mistakes

• Thinking sunlight is only white: It is a mix of many colours.
• Believing rainbows are painted in the sky: They are made by light bending in raindrops.
• Mixing up reflection and refraction: Both happen in a raindrop, but refraction (bending) is what splits the colours.
• Forgetting you need both sunlight and rain: No raindrops, no rainbow!

Remember it

Rainbows show up when sunlight bends and splits in raindrops, making all its hidden colours visible.