410 Diffraction Patterns and PolarizationQ38.17The fine hair blocks off light that would otherwise go through a fine slit and produce a diffractionpattern on a distant screen. The width of the central maximum in the pattern is inverselyproportional to the distance across the slit. When the hair is in place, it subtracts the same diffractionpattern from the projected disk of laser light. The hair produces a diffraction minimum that crossesthe bright circle on the screen. The width of the minimum is inversely proportional to the diameterof the hair. The central minimum is flanked by narrower maxima and minima. Measure the width 2yof the central minimum between the maxima bracketing it, and use Equation 38.1 in the form yLa=λto find the width aof the hair.Q38.18The condition for constructive interference is that the three radio signals arrive at the city in phase.We know the speed of the waves (it is the speed of light c), the angular bearing θof the city east of
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