The color to which the human eye is most sensitive is a yellowishgreen with a wavelength of approximately 550 nm. (For this"scientific" reason there was a brief vogue in the 1980s for makingfire trucks this color, a fad that faltered when departments foundthat firefighters took little pride in non-red fire trucks andconsequently maintained them poorly. In fact, the photographer ofthe accompanying picture was told that the truck will be paintedred "within a month red is traditional".) (a) What is thefrequency of waves of this color? (b) How many wavelengths of thisyellowish green light are there in the thickness of a human hairthat is 110 m in diameter? (c) How manywavelengths of the light are there in the width of a pencil,6.00 mm?
Explanation / Answer
(a) freq = speed / wavelength = 3 x 108 / 550 x 10-9 = 5.455 x1014 Hz . (b) number of wavelengths = 110 x10-6 / 550 x 10-9= 200 . (c) number of wavelengths = 0.006 / 550 x10-9= 10909