31. (i) What is visible spectrum ?
(ii) Why is red used as the stopping light at traffic signals ?
(iii) Two triangular glass prisms are kept together connected through their rectangular side. A
light beam is passed through one side of the combination. Will there be any dispersion?
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Answer. (ii) The primary reason why the color red is used for stopping at traffic signals is that red light is scattered the least by air molecules. The effect of scattering is inversely related to the fourth power of the wavelength of a color. ...
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(i) Term: Visible spectrum
Definition: The band of electromagnetic radiation that human eyes can detect. This ranges from wavelengths of approximately 400 to approximately 700 nanometers (nm.
(ii) The red colour is least scattered by fog or dust particles. So we can observe red colour easily even in foggy conditions. That is why stop signals have red colour.
(iii)No there wont be any dispersion.
Explanation:
Light get refracted when it changes medium. When the light changes medium there is a change in its speed, white light is mixture of lights of various wavelength, each wavelength is refracted at different angle. In case of refraction by a prism, it gets split into a band of light. But when two prisms are kept together and light is passed from one side, it doesn't emerges as a band of light on the other side, because the second prism merges the band created by the first one and turns it into white light.