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Question
What is the cause of the dispersion of white light through a glass prism? Draw a ray diagram to show the path of light when two identical glass prisms are arranged together in an inverted position with respect to each other and a narrow beam of white light is allowed to fall obliquely on one of the faces of the prisms.
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Solution
The dispersion of white light occurs because of the varying speeds of different colored lights through different media. White light consists of seven colors. The speeds of these colored lights are the same through the air. However, their speeds vary in other media. Therefore, when white light enters from air to a glass prism then its component colors get refracted by different angles. As a result, dispersion occurs.
A ray diagram to show the path of light when two identical glass prisms are arranged together in an inverted position with respect to each other and a narrow beam of white light is allowed to fall obliquely on one of the faces of the prisms is given below:
When white light of the Sun passes through the first prism, it gets dispersed into its seven component colors. When all the seven colors of the spectrum pass through the second prism then a beam of white light emerges from the other side of the second prism.
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RELATED QUESTIONS
A narrow beam PQ of white light is passing through a glass prism ABC as shown in the diagram.
Trace it on your answer sheet and show the path of the emergent beam as observed on the screen DE.
(i) Write the name and cause of the phenomenon observed.
(ii) Where else in nature is this phenomenon observed?
(iii) Based on this observation, state the conclusion which can be drawn about the constituents of white light.
Study the following diagrams in which the path of a ray of light passing through a glass prism as traced by four students P, Q, R and S is shown:
The student who has traced the path correctly is
(A) P
(B) Q
(C) R
(D) S
Describe an activity to show that colours of white light splitted by a glass prism can be recombined to get white light by another identical glass prism. Also draw ray diagram to show the recombination of the spectrum of white light.
Study the following figure in which a student has marked the angle of incidence (∠i), angle of refraction (∠r), angle of emergence (∠e), angle of prism (∠A) and the angle of deviation (∠D). The correctly marked angles are
(a) ∠A and ∠i
(b) ∠A, ∠i and ∠r
(c) ∠A, ∠i, ∠e and ∠D
(d) ∠A, ∠i, ∠r and ∠D
As light rays pass from air into a glass prism, are they refracted towards or away from the normal?
What are the seven colours seen in a rainbow?
A ray of light moving from an optically rarer to a denser medium
Distinguish between an impure spectrum and a pure spectrum.
Sunlight entering through a narrow aperture falls on a prism. Draw a neat labelled ray diagram to show the formation of the spectrum on a screen. Name the colour obtained nearer the base of the prism.
