Adding waves (of the same frequency) together

• When two sinusoidal waves with identical frequencies and wavelengths interfere, the result is another wave with the same frequency and wavelength, but a maximum amplitude which depends on the phase difference between the input waves.
• Constructive interference occurs when the phase difference between two waves is zero, or some multiple of pi radians
• Destructive interference occurs when the phase difference between two waves is some multiple of pi/2 radians
• Adding two sound waves which are out of phase may yield silence!
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    This would be a good time for a little demonstration of wave addition ....

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