Ch 17 Principle of Superposition and Interference Phenomena

Ch 17 Principle of Superposition and Interference Phenomena...

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The Principle of Superposition and Interference Phenomena Lecture Notes 17
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± To describe mechanical waves. ± To study superposition, standing waves and sound. ± To present sound as a standing longitudinal wave. ± To see that waves will interfere (add constructively and destructively). ± To study sound intensity and beats. ± To examine applications of acoustics and musical tones. Goals
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17.1 The Principle of Linear Superposition When the pulses merge, the Slinky assumes a shape that is the sum of the shapes of the individual pulses.
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17.1 The Principle of Linear Superposition When the pulses merge, the Slinky assumes a shape that is the sum of the shapes of the individual pulses.
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¾ Two waves come in from opposite directions. ¾ Each wave has amplitude inverted with respect to the other. ¾ During the superposition, there is nearly cancellation. ¾ After the collision, the outgoing waves resemble those that came in, with the sign of the amplitude inverted. ¾ The details are a complex function of time.
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Waves can Superimpose : Two transverse “up” pulses, passing through each other Two transverse pulses, one “up” and one “down”, passing through each other The Principle of Linear Superposition ± When two or more waves are present simultaneously at the same place, the resultant disturbance is the sum of the disturbances from the individual waves. ± The principle can be applied to all types of waves , including sound waves, water waves, and electromagnetic waves.
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Constructive and Destructive Interference of Sound Waves: Constructive interference between the two sound waves (amplitude= A ). A loud sound (amplitude = 2 A ) is heard at an overlap point located equally distant from two exactly in phase speakers (coherent sources). ± When two waves always meet condensation-to-condensation and rarefaction-to-rarefaction, they are said to be exactly in phase and to exhibit constructive interference.
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Destructive interference . Although the speakers vibrate in phase, the left speaker is one-half of a wavelength farther from the overlap point than the right speaker. Because of destructive interference, no sound is heard at the overlap point. The speakers are exactly out of phase.
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Ch 17 Principle of Superposition and Interference Phenomena...

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