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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.

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Student-friendly explanation

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.

How to write this in exams

  1. 1

    Start with the exact idea

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

  2. 2

    Then show how to use it

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

  3. 3

    Add one concrete example

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

  4. 4

    Avoid this incomplete answer

    A common wrong answer is that the prism adds colors to white light. That is wrong because the prism only separates the colors already present.

Definition

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

Example

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

Rule to remember

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

Memory hook

Prism separates, it does not create.

Examples and method

Worked example

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

Method to apply

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

Diagram support

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

How CBSE asks it

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

Avoid common mistakes

Common confusion

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

Common wrong answer

A common wrong answer is that the prism adds colors to white light. That is wrong because the prism only separates the colors already present.

Exam tip

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

Quick check

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

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.

Answer writing and exam use

1-mark answer

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

2-mark answer

Dispersion is the splitting of white light into its constituent colors when it passes through a prism or similar transparent medium. Dispersion happens because different colors have different refractive indices in the same medium. When sunlight passes through a glass prism, a band of seven colors appears on the screen.

3-mark answer

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. Dispersion happens because different colors have different refractive indices in the same medium. A ray of white light enters a prism. Red light bends the least, violet bends the most, and the screen receives a colored band instead of one white patch. Explain the splitting of white light through a prism, name the colors in order, or identify which color deviates most. A common wrong answer is that the prism adds colors to white light. That is wrong because the prism only separates the colors already present.
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