Question

A beam of white light falling on a glass prism gets split up into seven colours marked 1 to 7 as shown in the diagram. A student makes the following
statements about the spectrum observed on the screen:

(a) The colors at positions marked 3 and 5 are similar to
the color of the sky and the color of gold metal respectively. Is the above
statement made by the student correct or incorrect? Justify.
(b) Which two positions correspond closely to the color of:
(i) a Brinjal (ii) ‘danger’ or stop signal lights?
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Answer 1

Answers to the given questions are as follows:

(a). The statement made by the student is incorrect because the color marked 3 is yellow and the color marked 5 is blue. Hence, the statement is totally opposite.

(b).  (i).  a Brinjal -  7, violet.

(ii). 'danger' or stop signal lights - red.

Answer 2

(a) The statement made by student is false.

(b) (i) 7 is closely related to colour of brinjal; (ii) 1 is closely related to colour of 'danger'.

What is dispersion?

• When a ray of light is passed through a prism, it gets separated into
• seven visible wavelengths of light.
• This separation of white light into seven colours is called spectrum of light.
• Visible region of white light ranges from wavelength of 400 nm to 700 nm.

From the Figure:

• The order of colours in increasing wavelengths is: Violet, Indigo, Blue, Green, Yellow, Orange and Red.
• Red has the maximum wavelength and violet has the minimum wavelength.
• The maximum angle of bending is for violet colour and so position 7 represents violet colour and minimum bending angle is of red which is position 1.
• Accordingly, the colours corresponding to the position number are:

Violet - 7

Indigo - 6

Blue - 5

Green - 4

Yellow - 3

Orange - 2

Red - 1

• Number 3 is the colour of gold (Yellow) and number 5 is the colour of sky (Blue).