(a) Why do the faces of persons sitting opposite to us around a camp fire appear to shimmer?
(b) Why is red light used as universal danger signal?
Answers
Answer:
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Explanation:
(a) The faces of persons sitting opposite to us around a camp fire appear to shimmer because of the refraction of light. The reflected rays of light from the face of a person, sitting opposite to us, get refracted as they pass through the hot air (produced by the burning of wood). Fast moving hot air molecules cause the optical density to vary continuously. Thus, it causes the path of refracted rays passing through it to change continuously giving rise to a shimmering effect.
(b) The red light is least scattered by the atmosphere since it has the longest wavelength amongst the spectral colours. Hence, red light is able to pass easily through fog or mist, without getting scattered and hence is visible from a long distance. That is why; red light is used as universal danger signal.
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1)At a campfire, the density of the hot air near the flames is lower than that of the air farther away. Also, hot air is constantly moving up.
At a campfire, the density of the hot air near the flames is lower than that of the air farther away. Also, hot air is constantly moving up.So, at a campfire, the light reflected from the face of the opposite person first passes through the cooler air and then through the warmer air near the flames. As a result, it bends and the face of the person appears to change in brightness and position. This is what we call twinkling.
2)The primary reason why the color red is used for danger 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.These reasons make danger signals the most effective when they are painted in red.