What is ‘dispersion of white light’ ? State its cause. Draw a ray diagram to show the dispersion of white light by a glass prism.

Q: What is ‘dispersion of white light’ ? State its cause. Draw a ray diagram to show the dispersion of white light by a glass prism.

### Dispersion of White Light The splitting of white light into its seven component colours (Violet, Indigo, Blue, Green, Yellow, Orange, and Red) when it passes through a refracting medium like a glass prism is called **dispersion of light**. ### Cause of Dispersion Different colours of light have different wavelengths and travel with different speeds in a medium like glass, although they travel with the same speed in vacuum/air. When white light passes through a prism, different colours bend through different angles with respect to the incident ray. * **Red light** bends the least because it has the maximum speed in glass. * **Violet light** bends the most because it has the minimum speed in glass. This differential bending causes the constituent colours to emerge along different paths, making them distinct. ### Ray Diagram Below is the ray diagram showing the dispersion of white light by a glass prism: ```diagram {"xrange": [4.4, 475.6], "yrange": [-274.0, -26.0], "lines": [{"from": [150, -250], "to": [250, -50], "label": "Glass Prism"}, {"from": [250, -50], "to": [350, -250], "label": ""}, {"from": [50.0, -180.0], "to": [200.0, -150.0], "label": "White light beam"}, {"from": [200.0, -150.0], "to": [300.0, -140.0], "label": ""}, {"from": [200.0, -150.0], "to": [300.0, -170.0], "label": ""}, {"from": [300.0, -140.0], "to": [420.0, -120.0], "label": "Red (Bends least)"}, {"from": [300.0, -170.0], "to": [420.0, -220.0], "label": "Violet (Bends most)"}], "points": [{"x": 430.0, "y": -170.0, "label": ""}]} ```

Dispersion of white light by a glass prism

Official Answer

Dispersion of White Light

The splitting of white light into its seven component colours (Violet, Indigo, Blue, Green, Yellow, Orange, and Red) when it passes through a refracting medium like a glass prism is called dispersion of light.

Cause of Dispersion

Different colours of light have different wavelengths and travel with different speeds in a medium like glass, although they travel with the same speed in vacuum/air. When white light passes through a prism, different colours bend through different angles with respect to the incident ray.

Red light bends the least because it has the maximum speed in glass.
Violet light bends the most because it has the minimum speed in glass.

This differential bending causes the constituent colours to emerge along different paths, making them distinct.

Ray Diagram

Below is the ray diagram showing the dispersion of white light by a glass prism:

splitting of white lightcomponent coloursdispersiondifferent anglesred bends leastviolet bends mostspectrum

Marking Scheme

11 mark
21 mark
31 mark

Hint

Recall that white light is a mixture of seven colours. Each colour travels at a different speed inside glass, causing them to bend by different amounts.

Quick Oral Answer

Dispersion is the splitting of white light into its component colours when passing through a prism. It happens because different colours of light travel at different speeds in glass, causing them to bend at different angles.

Analysis & Explanation

According to the NCERT textbook, Isaac Newton first used a glass prism to obtain the spectrum of sunlight. The splitting of light into its component colours is defined as dispersion. The cause is rooted in the fact that different colours of light bend through different angles with respect to the incident ray as they pass through a prism. Red bends the least, while violet bends the most, creating a beautiful band of seven colours known by the acronym VIBGYOR.

Common Mistakes

1Confusing dispersion with atmospheric refraction.
2Drawing the red light bending more than the violet light.
3Forgetting to label the incident white light and the emergent spectrum.

Interesting Facts

A rainbow is a natural spectrum caused by the dispersion of sunlight by tiny water droplets in the atmosphere acting as miniature prisms.

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2017?

This question carries 3 marks in the CBSE Class 10 Science 2017 examination.

What topic does this question cover in Science?

This question covers the topic "Dispersion of white light by a glass prism" from CBSE Class 10 Science.

What type of question is this in the CBSE Class 10 Science 2017 paper?

This is a Short Answer question from Section A in the CBSE Class 10 Science 2017 paper.