Human Eye And The Colourful World Question 49

Question: Q. 7. What is “dispersion of white light” ? Draw a labelled diagram to illustrate the recombination of the spectrum of white light. Why is it essential that the two prisms used for the purpose should be identical and placed in an inverted position with respect to each other? [CBSE Outside Delhi Set III, 2017]

Show Answer

Solution:

  • Splitting of white light into seven colours. 1

  • Because the refraction / bending produced by second prism is equal to the refraction / bending produced by the first prism.

1

1

[CBSE Marking Scheme, 2017]

Detailed Answer:-

The phenomenon of splitting of white light into its constituent seven colours on passing through a glass prism is called dispersion of light.

It is essential that the two prisms used should be identical and placed in an inverted position with respect to each other because the extent of refraction produced by second prism is equal to the refraction produced by the first prism. The second prism acts in the opposite sense than that of the first one.

[3]

[AI Q. 8. (a) Draw a ray diagram to explain the term angle of deviation.

(b) Why do the component colour of incident white light split into a spectrum while passing through a glass prism, explain.

(c) Draw a labelled ray diagram to show the formation of a rainbow. A, AE [Delhi 31/1/1 2017]

Ans. (a)

(b) Different colour of white light bend through different angles with respect to the incident light, as they pass through the glass prism. Thus, each colour emerges along a different path, forming a spectrum.

(c)

[CBSE Marking Scheme, 2017]

Detailed Answer:

(a) Emergent ray bends at an angle to the direction of the incident ray and the angle between them is known as angle of deviation.



Table of Contents