medium importancemedium difficulty6 min

Rainbow

A rainbow is a natural spectrum of sunlight seen in the sky after dispersion, refraction, and internal reflection in water droplets.

In one line: Drop inside, colors outside.

Practice This Concept

Understand it

When sunlight enters a raindrop, it refracts and splits into colors. The light then reflects inside the drop and refracts again when it comes out. Because many drops send different colors toward the eye at different angles, a curved band of colors is seen in the sky.

Example

After rain, if the sun is behind you and water droplets are in front, a rainbow may appear in the opposite direction of the Sun.

Formula and rule

Rainbow formation requires dispersion, refraction, and internal reflection in spherical water droplets.

See it worked out

Follow the example line by line, then use the same method on new questions.

Worked example

1After a shower, sunlight enters suspended droplets.
2Red and violet rays emerge at different angles, so the observer sees a curved colored arc opposite the Sun.

Method you can reuse

1Sunlight enters a water droplet.
2It refracts and disperses into colors.
3The light reflects inside the droplet.
4It refracts again as it leaves the drop.
5Many such droplets together produce the rainbow.

Sketch it in your answer

Draw the Sun behind the observer, raindrops in front, and a light path showing entry, reflection, and exit with colored rays.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why does a rainbow appear opposite the Sun after rain?

Think first, then show answer

A rainbow appears opposite the Sun because sunlight enters water droplets, gets dispersed and reflected inside them, and then reaches the eye at specific angles. The eye sees the colored arc in the direction opposite the Sun.

Common wrong answer

A common wrong answer is to say that the rainbow is painted in the sky by clouds.

Why it loses marks: It is formed by light interacting with droplets.

Don't mix this up

Students often think a rainbow appears only because of rain and sunlight together. The important point is the specific path of light through water droplets.

Exam tip

In a 3-mark answer, mention refraction, dispersion, and internal reflection in water droplets.

Write it in the exam

Each point is worth about one mark. Write point 1 for a 1-mark question and keep adding points as the marks go up.

How CBSE asks it

Explain rainbow formation with a labelled ray path, or state the sequence of optical events in a raindrop.

1
Enough for 1 mark
A rainbow is a natural spectrum of sunlight seen in the sky after dispersion, refraction, and internal reflection in water droplets.
2
Add for 2 marks
When sunlight enters a raindrop, it refracts and splits into colors.
3
Add for 3 marks
The light then reflects inside the drop and refracts again when it comes out.

MCQ Quiz

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