12 Waves 3 - When two (or more) waves of the same kind...

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Unformatted text preview: When two (or more) waves of the same kind propagate through the same region, they produce a composite wave. This phenomenon is called interference . It is constructive , when the waves reinforce each other. It is destructive , when they reduce each others amplitude. Usually the disturbances (displacements) the waves produce are added algebraically . This is called superposition principle. Superposition principle: adding two square waves + ? Superposition principle: adding two harmonic waves + ? Superposition of pulses: Constructive Interference Superposition of pulses: Destructive Interference For a moment it the string becomes a straight line no disturbance is seen. Does the energy of wave motion disappear? Where does it go? How can the two waves go on after that? Two kinds of energy in the wave motion: potential depends on deflection of the string from the straight line; kinetic depends on velocity of motion of the string. In the very moment, when the string becomes straight, it is actually moving very fast - high K . http://www.kettering.edu/~drussell/Demos/superposition/superposition.html When there are two interfering waves with close but different frequency the result of the interference is the beats . They are perceived as a wave with an average frequency , but with a slowly oscillating amplitude . When there are two interfering waves with close but different frequency the result of the interference is the beats . They are perceived as a wave with an average frequency , but with a slowly oscillating amplitude . ] ) ( 2 1 cos[ ] ) ( 2 1 cos[ 2 ) ( 2 1 2 1 t t A t y + = ) cos( ) ( 1 1 t A t y = ) cos( ) ( 2 2 t A t y = ) cos( ) cos( ) ( ) ( ) ( 2 1 2 1 t A t A t y t y t y + = + = The resulting composite wave: When there are two interfering waves with close but different...
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This note was uploaded on 12/13/2011 for the course PHYS 2C PHYS 2C taught by Professor Groisman during the Spring '11 term at UCSD.

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12 Waves 3 - When two (or more) waves of the same kind...

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