Question

Two speakers are driven by the same oscillator with frequency of 140 Hz. They are located 4.00 m apart on a vertical pole. A man walks straight toward the lower speaker in a direction perpendicular to the pole. He will hear the minimum in sound intensity twice.
How far is he from the pole at these moments?

Answer 1

When is the difference in distances equal to half a wavelength or 1.5 wavelengths?

Look up velocity of sound call it c
then period = 1/f = L/c where L is wavelength
Calculate L from that

say man is x meters from pole
distance to lower speaker is x
distance from higher speaker is
sqrt (x^2+4^2)
difference = sqrt(x^2+4^2) - x
when is that equal to L/2 ??