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Dispersion

Dispersion is the splitting of white light into its constituent colors when it passes through a prism or similar transparent medium.

In one line: Prism separates, it does not create.

Practice This Concept

Understand it

White light contains many colors, and different colors bend by different amounts in a prism because each color travels with a slightly different speed in the medium. Violet deviates the most and red deviates the least. This separation of colors is called dispersion.

Example

When sunlight passes through a glass prism, a band of seven colors appears on the screen.

Formula and rule

Dispersion happens because different colors have different refractive indices in the same medium.

See it worked out

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

Worked example

1A ray of white light enters a prism.
2Red light bends the least, violet bends the most, and the screen receives a colored band instead of one white patch.

Method you can reuse

1State that white light falls on a prism.
2Explain that different colors bend by different amounts.
3Mention that violet deviates most and red least.
4Conclude that the beam separates into a spectrum.
5Name the phenomenon as dispersion.

Sketch it in your answer

Draw a prism with an incident white beam and an emergent spectrum labeled red, orange, yellow, green, blue, indigo, violet.

Check yourself

Answer the question in your head before opening the answer.

Try it yourself

Why does white light split into different colors after passing through a prism?

Think first, then show answer

White light splits because different colors bend by different amounts in the prism. Since each color has a different deviation, the white beam separates into a spectrum.

Common wrong answer

The prism adds colors to white light.

Why it loses marks: The prism only separates the colors already present.

Don't mix this up

Students sometimes say a prism creates colors from nothing. In reality, the colors were already present in white light and were only separated.

Exam tip

In board answers, mention unequal deviation of colors and the order red to violet.

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 the splitting of white light through a prism, name the colors in order, or identify which color deviates most.

1
Enough for 1 mark
Dispersion is the splitting of white light into its constituent colors when it passes through a prism or similar transparent medium.
2
Add for 2 marks
Example: When sunlight passes through a glass prism, a band of seven colors appears on the screen.
3
Add for 3 marks
White light contains many colors, and different colors bend by different amounts in a prism because each color travels with a slightly different speed in the medium.

MCQ Quiz

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