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Colour and Dispersion
Dispersion separates white light because different wavelengths refract differently.
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Colour and Dispersion
White light contains many colours.
A prism bends different colours by different amounts, so they spread out into a spectrum.
Recommended for Class 10
Colour and Dispersion
White light is a mixture of many visible wavelengths.
Different visible wavelengths are perceived as different colours.
Dispersion
Dispersion is the separation of white light into its component colours because different wavelengths are refracted by different amounts.
A glass prism can produce a visible spectrum.
Spectrum
A common visible sequence is:
red → orange → yellow → green → blue → violet
Why Colours Separate
The refractive index of glass varies slightly with wavelength.
Therefore, different colours travel at different speeds inside the material and are refracted by different amounts.
Red and Violet
In ordinary glass:
red light is generally deviated less;
violet light is generally deviated more.
Rainbow
Rainbows involve refraction, dispersion, and internal reflection in water droplets.
Colour of Objects
An object appears a particular colour because it reflects or transmits certain wavelengths more strongly than others.
A red object under white light reflects mainly red wavelengths and absorbs many others.
Colour and Dispersion — Advanced
Dispersion occurs because refractive index depends on wavelength.
The phase velocity of different wavelengths differs inside a material, causing wavelength-dependent refraction.
Common Mistakes
Common Mistakes
- Mistake
A prism does not "create" colours from nothing.
- Mistake
White light already contains the visible wavelength range.
- Mistake
Colour and brightness are not the same concept.
Revision Zone
60-Second Revision
Quick cues from this topic — use them for last-minute revision.
White light → many wavelengths.
Dispersion → colour separation.
Red → less deviation.
Violet → more deviation.
- Definition
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Practice
PQ
Q1. Define dispersion.
PQ
Q2. Why does a prism produce a spectrum?
PQ
Q3. Which colour bends more in ordinary glass, red or violet?
PQ
Q4. Does a prism create colours?
PQ
Q5. Name three processes involved in rainbow formation.
Exam Practice
EQ
Q1. Define dispersion.
EQ
Q2. Explain why different colours bend differently.
EQ
Q3. Compare red and violet deviation in a prism.
EQ
Q4. Explain the basic formation of a rainbow.
EQ
Q5. Why does a red object appear red?
School-standard facts for Matric and Intermediate. Original explanations — not copied from textbooks.