prelab4

prelab4 - 12. PRELAB FOR INTERFERENCE LAB 1. INTRODUCTION...

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12: Interference Lab - 1 12. PRELAB FOR INTERFERENCE LAB 1. INTRODUCTION As you have seen in your studies of standing waves, a wave and its reflection can add together “ constructively ” (peak meets peak, giving large amplitude) or destructively ” (peak meets valley, canceling each other). This type of adding is called INTERFERENCE , and it depends on the relative phase of the interfering waves. Since the direct and reflected waves are coming from the same source, they clearly start out in phase . Whether or not they come back together in phase depends on path length. If the difference in the two path lengths is 1,2,3,etc. wavelengths , then the waves will be back in phase. If there is an extra ½ wavelength, however, they will be out of phase. 2. AN EXAMPLE OF MICROPHONE PLACEMENT The next page contains an excerpt from an article on the importance of a microphone placement. Read the excerpt and answer the following questions: 1. When the pressure wave is reflected from the table, is there a 180 o phase shift? (Think back to the standing waves in the open and closed tubes). 2. Look at Fig. 4.10 from the excerpt. Suppose that the direct sound travels 2 meters, and the reflected sound covers a greater distance of 2 ½ meters. Therefore, the difference in the two path lengths is d = 0.5m. Constructive interference will occur when d = λ , 2 λ , 3 λ , 4 λ , … , where λ is the wavelength. Use the relation v = λ f , (v – speed of sound, f – frequency) to calculate the first four frequencies at which constructive interference will occur. Assume v = 344 m/s. Then, calculate the first four frequencies at which destructive interference ( d = ½ λ , (1+ ½) λ , (2+ ½) λ , …) will occur.
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This note was uploaded on 01/20/2012 for the course P 109 taught by Professor Staff during the Fall '08 term at Indiana.

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prelab4 - 12. PRELAB FOR INTERFERENCE LAB 1. INTRODUCTION...

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