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CraftExam
medium importancemedium difficulty6 min

Scattering

Scattering is the redirection of light in many directions when light hits tiny particles in a medium.

In one line: Short waves scatter more, so blue spreads more.

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Understand it

When sunlight enters the atmosphere, tiny dust particles and gas molecules scatter the light. Shorter wavelengths such as blue scatter more strongly than longer wavelengths like red. That is why the sky looks blue in the daytime and why the Sun looks red at sunrise and sunset.

Example

On a clear day, the sky appears blue because blue light is scattered strongly by air molecules.

Formula and rule

Shorter wavelength light is scattered more strongly than longer wavelength light in the atmosphere.

See it worked out

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

Worked example

  1. 1When white sunlight enters the atmosphere, blue light is scattered in all directions.
  2. 2That scattered blue light reaches the eye from every part of the sky, so the sky appears blue.

Method you can reuse

  1. 1State that tiny particles scatter sunlight.
  2. 2Mention that shorter wavelengths scatter more.
  3. 3Connect blue light to the blue sky.
  4. 4Connect red light to sunrise and sunset.
  5. 5Name the process as scattering.

Sketch it in your answer

Draw the Sun, atmospheric particles, and many scattered blue rays reaching an observer from different directions.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why does the daytime sky usually look blue to us?

Think first, then show answer
The sky looks blue because air molecules scatter shorter wavelengths of sunlight more strongly than red light. Blue light is spread in many directions and reaches our eyes from the sky more easily.

Common wrong answer

A common wrong answer is to say that the atmosphere is naturally blue like paint.

Why it loses marks: Sky color comes from scattered sunlight.

Don't mix this up

Students often think the sky is blue because the atmosphere itself is blue. The color is due to scattering of sunlight, not because air has color.

Exam tip

For a strong answer, mention that shorter wavelengths scatter more and connect it to sky color.

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 blue sky or red sunrise/sunset, or compare scattering of blue and red light in the atmosphere.
  1. 1

    Enough for 1 mark

    Scattering is the redirection of light in many directions when light hits tiny particles in a medium.

  2. 2

    Add for 2 marks

    Example: On a clear day, the sky appears blue because blue light is scattered strongly by air molecules.

  3. 3

    Add for 3 marks

    When sunlight enters the atmosphere, tiny dust particles and gas molecules scatter the light.

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