B3 INTERFERENCE OF ULTRASONIC WAVES

B3 INTERFERENCE OF ULTRASONIC WAVES - EXPERIMENT...

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EXPERIMENT INTERFERENCE OF ULTRASONIC WAVES Introduction: All wave phenomena exhibit the four characteristics of Reflection, Refraction, Diffraction, and Interference. It should be remembered that sound waves are longitudinal in which the vibration of the particles of the medium is along the same direction as the motion of the wave. Sound waves are in fact pressure vibrations in the medium. A series of compressions and expansions (rarefactions) propagate along the direction of wave motion. Human ear respond to frequencies in the range of 20 Hz to about 20,000 Hz . This is called the audible range. These limits vary somewhat from one individual to another. Frequencies above 20,000 Hz are called ultrasonic ( do not confuse with supersonic, which is used for an object moving with a speed faster than the speed of sound). Many animals can hear ultrasonic frequencies; dogs, for example, can hear sounds as high as 50,000 Hz , and bats can detect frequencies as high as 100,000 Hz . Sound waves whose frequencies are below the audible range (i.e. less than 20 Hz ) are called infrasonic . In this experiment the wave character of sound will be investigated by studying the interference pattern some distance away from two sources emitting ultrasonic waves. It is well known that when two waves travel along different paths, the path length difference can alter their phase difference, as shown in Fig.1. A A Y 2 Y 1 B B Figure 1: Sound waves of the same frequency and phase from sources A and B constructively interfere at Y 1 and destructively interfere at Y 2 The ultrasonic waves, are produced from two transducers located at a distance d apart and driven by a common 40 kHz sine wave generator so that they emit an identical frequency and are in phase. At a distance D from the line AB of the two transmitters, another ultrasonic transducer is used as a detector as shown in Fig.2. [ N.B. A transducer is a device that converts one type of energy into another, for example the loudspeaker, microphone, …etc. It is often used for measuring particular quantities, for example the thermocouple, …etc].
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B3 INTERFERENCE OF ULTRASONIC WAVES - EXPERIMENT...

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