大物机械波PPT.pptVIP

Wave Shape Illustration /upload/file/2_20041012222123_zhubo.swf Suppose the harmonic vibration function of two coherent wave sources S1 and S2 is respectively S1 S2 r1 r2 the harmonic vibration function caused by two wave at point P is respectively the net vibration function of medium element at point P is Interference constructively（in phase）： Interference destructively（in opposite): is called the difference of wave path. If： Then： Interference constructively Interference destructively Example As shown in figure, A and B are two coherent wave sources separated by 30m. Their amplitudes both are A, angular frequency is ω=100Hz, the difference of phase is π. Find the points where are at rest due to interference. Vibration equation of A ： Wave function of A ： Vibration equation of B ： Wave function of B ： 8. Standing waves Imagine that we have two waves that are identical except that they are traveling in opposite directions in the same medium. Play flash. u u nodes + - antinodes If we ignore any phase angle φ for simplicity, the wave functions for the two waves can be written The resultant wave function : 2. antinodes, nodes The position of maximum amplitude is called antinodes. Note that adjacent antinodes are separated by a distance of These points of zero amplitude are called nodes. Nodes are also spaced by . The distance from nodes to antinodes is . X Y o b c d a Angular wave number k Physical meaning: the phase of per unit length along the wave line. Physical meaning: the phase of per unit time. Angular wave number k is often called simply the wave number. Contrast How to find the wave function: Find vibration function of reference point. Find the vibration function of freewill vibrator according to the relationship of phase advance or relay . That is the wave equation. Physical Meaning of wave function (1). If x in the harmonic wave function is given, then the harmonic wave