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December 18, 2014

Homework Help: Physics waves

Posted by susan on Saturday, February 17, 2007 at 5:06pm.

Two sinusoidal waves travel in the same direction and have the same frequency. Thier amplitudes are Y1 and Y2. The smallest possible amplitude of the resultant wave is:
a) Y1+Y2 and occurs if they are 180 degrees out of phase
b) [Y1-Y2] and occurs if they are 180 degrees out of phase
c) Y1 + Y2 and occurs if they are in phase
d) [y1-Y2] and occurs if they are in phase
e) [Y1-Y2] and occurs if they are 90 out of phase.

I think the answer would be A if Y1 +Y2 and they are 180 degrees out of phase. I choose the answer based on the fact that superposition is based on the Y1 +Y2= resultant. So if the waves were out of phase they would produce the smallest resultant because the other is the complete reverse of the other. I thinking deconstruction.

Two identical waves but separate string, with the same tension carry sinusoidal waves with the same frequency. Wave A has an amplitude that is twice that of wave B and transmits energy at a rate that is _____ that of wave B.
a) half
b) twice
c) one-fourth
d) four times
e) eight times


iI thought the answer would be B because the amount of energy carried by a wave is related to the amplitude of the wave. A high energy wave is characterized by a high amplitude; a low energy wave is characterized by a low amplitude. The amplitude of a wave refers to the maximum amount of displacement of a a particle on the medium from its rest position. The energy imparted to a pulse will only effect the amplitude of that pulse.

Thank you for any help.

Your reasoning on the first is exact, but the answers are sloppy written, I think b more closely fits your reasoning.
The second : energy is proportional to amplitude squared, so if one is double amplitude, it is four times as much energy.

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