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Rainbow

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

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Student-friendly explanation

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.

How to write this in exams

  1. 1

    Start with the exact idea

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

  2. 2

    Then show how to use it

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

  3. 3

    Add one concrete 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.

  4. 4

    Avoid this incomplete answer

    A common wrong answer is to say that the rainbow is painted in the sky by clouds. That is wrong because it is formed by light interacting with droplets.

Definition

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

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.

Rule to remember

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

Memory hook

Drop inside, colors outside.

Examples and method

Worked example

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

Method to apply

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

Diagram support

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

How CBSE asks it

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

Avoid common mistakes

Common confusion

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.

Common wrong answer

A common wrong answer is to say that the rainbow is painted in the sky by clouds. That is wrong because it is formed by light interacting with droplets.

Exam tip

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

Quick check

Why does a rainbow appear opposite the Sun after rain?

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.

Answer writing and exam use

1-mark answer

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

2-mark answer

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

3-mark answer

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. Rainbow formation requires dispersion, refraction, and internal reflection in spherical water droplets. After a shower, sunlight enters suspended droplets. Red and violet rays emerge at different angles, so the observer sees a curved colored arc opposite the Sun. Explain rainbow formation with a labelled ray path, or state the sequence of optical events in a raindrop. A common wrong answer is to say that the rainbow is painted in the sky by clouds. That is wrong because it is formed by light interacting with droplets.
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