AP Physics B : Understanding Period and Amplitude

Study concepts, example questions & explanations for AP Physics B

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Example Questions

Example Question #1 : Understanding Period And Amplitude

Two in-phase waves travelling in the same direction with the same period have amplitudes of  and , respectively. A third, out-of-phase wave with the same period as the other two has an amplitude of . What will be the amplitude of the final resultant wave when these three are aligned?

Possible Answers:

Correct answer:


The amplitudes of in-phase waves add in what is called constructive interference. We can find the resultant amplitude of the first two waves by adding their individual amplitudes.

The third wave is out of phase, meaning that it will contribute destructive interference when the three waves align. We subtract the amplitude of the third wave from the total of the first two.

This is the final amplitude of the resultant wave.

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