Draw a labelled ray diagram to illustrate the dispersion of a narrow beam of white light when it passes through a glass prism.
Draw a labelled ray diagram to illustrate the dispersion of a narrow beam of white light when it passes through a glass prism.
When a narrow beam of white light passes through a glass prism, it splits into its seven constituent colours: Violet, Indigo, Blue, Green, Yellow, Orange, and Red (VIBGYOR). This phenomenon is called dispersion.
Different colours of light bend through different angles with respect to the incident ray as they pass through the prism because they travel at different speeds in glass. Red light travels the fastest in glass and bends the least, while violet light travels the slowest and bends the most.
Marking Scheme
- 1Drawing a neat, labelled diagram showing a glass prism, incident white light, and the dispersed spectrum on a screen. (1 mark)
- 2Correctly labelling the positions of Red (at the top / bending least) and Violet (at the bottom / bending most). (1 mark)
Hint
Remember the acronym VIBGYOR. Red is at the top of the spectrum (bends the least) and Violet is at the bottom (bends the most).
Quick Oral Answer
Dispersion is the splitting of white light into its component colours when it passes through a glass prism. Red light bends the least, and violet light bends the most.
Analysis & Explanation
Dispersion occurs because the refractive index of glass is different for different wavelengths (colours) of light. Since speed , where is the refractive index, different wavelengths experience different refractive indices, causing them to refract at different angles. Red light has the longest wavelength in the visible spectrum, experiences the lowest refractive index, and thus deviates the least. Violet light has the shortest wavelength, experiences the highest refractive index, and deviates the most.
Common Mistakes
- 1Inverting the spectrum by drawing violet at the top and red at the bottom.
- 2Forgetting to label the incident beam as 'white light' or omitting the screen.
Interesting Facts
Sir Isaac Newton used a second, identical inverted glass prism to show that the seven colours of the spectrum could be recombined back into a single beam of white light, proving that white light is inherently composed of these seven colours.
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2012?
This question carries 2 marks in the CBSE Class 10 Science 2012 examination.
Which chapter does this question come from in Science?
This question is from the chapter "The Human Eye and the Colourful World" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Refraction of Light through a Prism" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2012 paper?
This is a Short Answer question from Section A in the CBSE Class 10 Science 2012 paper.