Third Harmonic for Waves in a Tube

by Patrick Ford
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Hey, guys, let's do an example. Calculate the third largest frequency for a standing sound wave in a 0.2 m tube at 20 degrees Celsius. If a both ends are open or B one end disclosed. If both ends air open, this is node node. Remember, an open end is a pressure node. If one end is closed, this is a node Anti node. Remember, the closed ins are pressure anti nodes. Okay, so part A f n for node node is envy over to El, where in can be any integer. So what's the third largest? The third harmonic and could be 12 or three. So the third largest is the third harmonic. If the temperature is 20 degrees Celsius, then the speed is gonna be 3. 31 times one plus 20 over to 73 which is gonna be meters per second. So the speed is sorry in the harmonic numbers three, that's the third largest harmonic. The speed of sound is 343 m per second and the length is 0.2 m. And so this is 25, hurts. Okay, but now what if one end is closed? Now we have to use the note Anti note equations where f n is envy. Over four l. And what is the third largest harmonic? Well, in can be 13 and then five. It has to be odd. So the third largest harmonic is five. So the fifth harmonic is five times 3. 45/4 times 0.2 And this is 21 hurts. All right, that wraps up this problem. Thanks for watching guys.