Explanation:
Interference and Beats
Interference and Beats
The Doppler Effect and Shock Waves
Boundary Behavior
Reflection, Refraction, and Diffraction
Wave interference is the phenomenon that occurs when two waves meet while traveling along with the same medium. The interference of waves causes the medium to take on a shape that results from the net effect of the two individual waves upon the particles of the medium. As mentioned in a previous unit of The Physics Classroom Tutorial, if two upward displaced pulses having the same shape meet up with one another while traveling in opposite directions along with with a medium, the medium will take on the shape of an upward displaced pulse with twice the amplitude of the two interfering pulses. This type of interference is known as constructive interference. If an upward displaced pulse and a downward displaced pulse having the same shape meet up with one another while traveling in opposite directions along with a medium, the two pulses will cancel each other's effect upon the displacement of the medium and the medium will assume the equilibrium position. This type of interference is known as destructive interference. The diagrams below show two waves - one is blue and the other is red - interfering in such a way to produce a resultant shape in a medium; the result is shown in green. In two cases (on the left and in the middle), constructive interference occurs and in the third case (on the far right, destructive interference occurs.
Now if two sound waves interfere at a given location in such a way that the compression of one wave meets up with the rarefaction of a second wave, destructive interference results. The net effect of compression (which pushes particles together) and a rarefaction (which pulls particles apart) upon the particles in a given region of the medium are to not even cause a displacement of the particles. The tendency of the compression to push particles together is canceled by the tendency of the rarefactions to pull particles apart; the particles would remain at their rest position as though there wasn't even a disturbance passing through them. This is a form of destructive interference. Now if a particular location along with the medium repeatedly experiences the interference of compression and rarefaction followed up by the interference of rarefaction and impression, then the two sound waves will continually cancel each other and no sound is heard. The absence of sound is the result of the particles remaining at rest and behaving as though there was no disturbance passing through it. Amazingly, in a situation such as this, two sound waves would combine to produce no sound. As mentioned in a previous unit, locations along with the medium where destructive interference continually occurs are known as nodes.
