If we assume the energy spreads out equally in
all directions, the intensity obeys the inverse square law.
(a) Distance increases by a factor of 20/15 = 1.33
Intensity reduces by 1.33² = 1.77
Ratio of intensities is 1/1.77 =0.56
(b) The intensity is proportional to amplitude
squared, so amplitude is proportional to the square root of intensity. √1.77 = 1.33
Ratio of amplitudes is 1/1.33
Apr 4th, 2015
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