Question

The colour of the red glass in traffic signals is due to:
(A) $ S{{b}_{2}}{{S}_{3}}. $
(B) $ Hg{{I}_{2}}. $
(C) $ CdS. $
(D) $ CdSe. $

Answer 1

Hint: We know that in order to deal with this question first we will use the property of VIBGYOR and the manner in which it is written in terms of wavelength and frequency further we will use the concept of scattering that scattering is the inversely proportional to the wave length.

Complete answer:
First we will consider the term VIBGYOR, we can notice that red is at last, which means that the red colour has the highest wavelength amongst the scattering of white light. For a particular colour, the scattering effect is inversely proportional to the power of wavelength. If the wavelength decreases then the scattering increases. As violet colour has the least wavelength so the scattering for violet is maximum.
As violet colour has the least wavelength so the scattering for violet is maximum. Since red has the highest wavelength of all the colors, it is scattered the least. Therefore, it can travel the longest distance and can penetrate through rain, mist and fog. The main reason the red color in the traffic signals is used to stop the vehicle is because the air molecules disperse the least red. Hence, in traffic signals red colour light is used to stop vehicles because it has the highest wavelength.
The colour of the red glass in traffic signals is due to cadmium selenide or $ CdSe. $ Red glass can also be obtained by adding trace amounts of gold and copper.
Therefore the correct answer is option D.

Note:
Remember that the term VIBGYOR is special in the sense that the colours are arranged in this term in the increasing order of wavelength and decreasing order of frequency. The property that blue side colour is scattered the most is the reason behind the natural phenomenon such as blue colour of sky and blue colour of water.