Dispersion of Light
1.0Master Dispersion of Light in Minutes
Understand how a simple glass prism transforms white light into a beautiful spectrum of seven colours. Learn the science behind dispersion of light, explore why different colours bend differently, discover the formation of rainbows, and master this important CBSE Class 10 Physics concept with easy explanations and exam-focused learning.
2.0Learning Outcomes
After completing this lesson, you will be able to:
- Define dispersion of light and explain why it occurs.
- Describe how a prism splits white light into its constituent colours.
- Explain the formation of the spectrum (VIBGYOR).
- Differentiate between dispersion and refraction of light.
- Understand why different colours deviate by different amounts.
- Explain the formation of a rainbow using the concept of dispersion.
- Apply the concept of dispersion to solve CBSE board examination questions.
3.0Overview of Dispersion of Light
Have you ever wondered why a rainbow appears in the sky after rainfall? Or why a glass prism splits a beam of white light into seven beautiful colours?
These fascinating natural phenomena occur because of a property of light known as dispersion. Dispersion helps us understand that white light is actually a combination of many different colours, each having its own wavelength and behaviour.
The concept of Dispersion of Light is an important part of the CBSE Class 10 Science chapter "The Human Eye and the Colourful World." It explains how light behaves inside transparent materials and lays the foundation for understanding several optical phenomena encountered in everyday life.
4.0What is Dispersion of Light?
Dispersion of light is the phenomenon in which white light splits into its constituent colours when it passes through a transparent medium such as a glass prism.
In simple words:
"Dispersion is the splitting of white light into seven colours (VIBGYOR) due to different amounts of refraction experienced by each colour."
Each colour of white light has a different wavelength. Since different wavelengths travel at different speeds inside glass, they bend by different amounts, resulting in the formation of a colourful spectrum.
5.0Dispersion of White Light Through a Prism
The most common demonstration of dispersion uses a triangular glass prism.
When a narrow beam of white light enters one face of the prism:
- The light slows down as it enters the glass.
- Each colour refracts by a different angle.
- The colours gradually separate from one another.
- As the light emerges from the second face of the prism, seven distinct colours become visible.
This coloured band is known as the spectrum.
The experiment performed by Sir Isaac Newton proved that white light is composed of several colours and that a prism merely separates these colours instead of creating them.
6.0Spectrum of White Light
The band of seven colours obtained after the dispersion of white light is called the spectrum.
The colours always appear in the same order:
- Violet
- Indigo
- Blue
- Green
- Yellow
- Orange
- Red
This sequence is remembered using the acronym:
VIBGYOR
Characteristics of the Spectrum
It contains seven visible colours.
- Every colour has a different wavelength.
- Each colour has a different frequency.
- Every colour bends by a different amount while passing through the prism.
- The spectrum demonstrates that white light is not a single colour but a mixture of many colours.
7.0Why Do Different Colours Bend Differently?
Dispersion occurs because different colours have different wavelengths.
Since the refractive index of glass varies for different wavelengths:
- Violet light slows down the most inside the prism.
- Red light slows down the least.
This is why violet appears at one end of the spectrum and red appears at the other.
8.0Why Does Violet Deviate More Than Red?
Violet light has the shortest wavelength among the visible colours.
Because of its shorter wavelength:
- It experiences a higher refractive index.
- It travels more slowly inside the prism.
- It bends more towards the normal.
Red light has the longest wavelength, so:
- It travels comparatively faster inside glass.
- It experiences less refraction.
- It deviates the least.
This difference in deviation is responsible for the formation of the complete spectrum.
9.0Factors Affecting Dispersion of Light
The amount of dispersion produced depends upon several factors.
1. Nature of the Material: Different materials have different refractive indices. A prism made of flint glass produces greater dispersion than one made of ordinary glass.
2. Wavelength of Light: Colours with shorter wavelengths experience greater deviation.
Therefore: Violet deviates the most. Red deviates the least.
3. Shape and Angle of the Prism: The angle of the prism determines how much the colours spread apart. A prism with a larger refracting angle generally produces greater dispersion.
4. Refractive Index of the Medium: The greater the refractive index of the material, the greater will be the bending of light and the more noticeable the dispersion.
10.0Difference Between Refraction and Dispersion
Although both involve bending of light, refraction and dispersion are different phenomena.
Refraction | Dispersion |
|---|
Refraction is the bending of light when it passes from one medium to another. | Dispersion is the splitting of white light into seven colours. |
It can occur with a single colour of light. | It occurs mainly with white light. |
Only the direction of light changes. | Both direction and separation of colours occur. |
Caused by change in the speed of light. | Caused because different colours travel at different speeds inside the medium. |
11.0Dispersion of Light in Real Life
Dispersion is not just a laboratory experiment—it explains many beautiful natural phenomena and has several practical applications in science and technology.
1. Formation of a Rainbow
A rainbow is the most common example of dispersion in nature. When sunlight passes through tiny water droplets suspended in the atmosphere, it undergoes refraction, dispersion, internal reflection, and refraction again. This separates white light into seven colours, forming a rainbow.
2. Formation of Spectrum
When white light passes through a glass prism, it splits into a band of seven colours called the spectrum. This experiment demonstrates that white light is a combination of different colours.
3. Spectroscopy
Scientists use the principle of dispersion in spectrometers to study the composition of stars, planets, and various chemical substances. Every element produces a unique spectrum that helps identify it.
4. Optical Instruments
Prisms are used in optical devices such as binoculars, telescopes, cameras, and periscopes to manipulate and separate light efficiently.
5. Scientific Research
Dispersion helps researchers analyze light emitted or absorbed by different substances, making it an important tool in astronomy, chemistry, and physics.
12.0Rainbow Formation
A rainbow is formed due to the combined effects of refraction, dispersion, and internal reflection inside tiny raindrops.
Formation Process
Step 1: Sunlight enters a raindrop and undergoes refraction.
Step 2: White light splits into seven colours because of dispersion.
Step 3: The dispersed colours undergo internal reflection inside the water droplet.
Step 4: As the colours emerge from the droplet, they undergo refraction again and become visible as a rainbow.
Interesting Facts
- A rainbow always appears opposite the Sun.
- Red colour forms the outer edge of the rainbow.
- Violet colour forms the inner edge.
- Every observer sees a unique rainbow depending on their position.
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14.0Supporting Study Materials
Strengthen your understanding of Dispersion of Light with comprehensive CBSE Notes, NCERT Solutions, chapter-wise practice questions, and previous years' board questions. These resources are prepared according to the latest CBSE Class 10 Science syllabus and help students build conceptual clarity while improving problem-solving skills for school and competitive examinations.
15.0Previous Year Questions on Dispersion of Light
Question 1: Why does a glass prism split white light into seven colours?
Answer: A glass prism splits white light because each colour has a different wavelength and experiences a different refractive index inside the prism. As a result, every colour bends by a different amount, producing the spectrum of seven colours (VIBGYOR).
Question 2: Why does violet light deviate more than red light when passing through a prism?
Answer:: Violet light has the shortest wavelength and experiences a higher refractive index in glass. Therefore, it bends more while passing through the prism. Red light has the longest wavelength and bends the least.
16.030-Second Quick Review: Dispersion of Light
- Dispersion is the splitting of white light into seven constituent colours.
- It occurs when white light passes through a glass prism.
- The seven colours are Violet, Indigo, Blue, Green, Yellow, Orange, and Red (VIBGYOR).
- Violet has the shortest wavelength and deviates the most.
- Red has the longest wavelength and deviates the least.
- The coloured band produced is called the spectrum.
- Dispersion occurs because different colours have different refractive indices.
- A rainbow is formed due to refraction, dispersion, and internal reflection of sunlight in raindrops.
- Dispersion is different from refraction because it separates white light into colours.
- Sir Isaac Newton demonstrated that white light is a mixture of seven colours.
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