When we place a glass prism in the path of a narrow beam of white light a spectrum is obtained. What happens when a second identical prism is placed in an inverted position with respect to the first prism ? Draw a labelled ray diagram to illustrate it.
When we place a glass prism in the path of a narrow beam of white light a spectrum is obtained. What happens when a second identical prism is placed in an inverted position with respect to the first prism ? Draw a labelled ray diagram to illustrate it.
When a second identical glass prism is placed in an inverted position with respect to the first prism, the dispersed spectrum of seven colours enters the second prism. The second prism recombines all the colours to form a single beam of white light that emerges from its other side. This phenomenon is known as the recombination of the spectrum of white light.
Here is the labelled ray diagram illustrating this phenomenon:
Marking Scheme
- 1Explanation of recombination (dispersed light recombines to form white light): [1 mark]
- 2Correctly drawn and labelled ray diagram showing two prisms (one upright, one inverted) and the path of light: [1 mark]
Hint
Recall Isaac Newton's experiment on the recombination of the spectrum of white light using two identical prisms.
Quick Oral Answer
When we place an inverted prism after the first one, the second prism reverses the dispersion caused by the first prism, recombining the seven colours back into a single beam of white light.
Analysis & Explanation
Isaac Newton showed that when white light passes through a triangular glass prism, it splits into its seven constituent colours (dispersion). When an identical second prism is placed in an inverted position, it acts in opposition to the first prism. The refraction at the surfaces of the second prism bends the different coloured rays back together, recombining them into a single beam of white light.
Common Mistakes
- 1Drawing both prisms in the same orientation.
- 2Not labelling the red and violet rays or the final emergent white light.
Interesting Facts
Sir Isaac Newton performed this experiment to prove that white light is not created by the prism itself, but is actually composed of seven constituent 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.
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 2012 paper?
This is a Short Answer question from Section A in the CBSE Class 10 Science 2012 paper.