Physics Labs on the Speed of a Wave

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Physics labs on the speed of a wave always require you to keep a few key things in mind. Find out about physics labs on the speed of a wave with help from an applied physics professional in this free video clip.

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Video Transcript

Hello, my name is Walter Unglaub, and this is "physics labs on the speed of a wave." So, here, I have a diagram that represents a wave tank. It's a tank with some water, filled to some height, H, and the length of the tank is length L, And, on this end, I'm going to have some sort of paddle, or something that generates the motion of the water in this direction. Because of these boundary conditions, however, as the water wave propagates along this direction, it will reflect and come back. But, if you keep moving the paddle, then you're going to have interfering waves. If you match the resonance condition, which is given by KL is equal to N pi, then you can create standing wave patterns. So, standing wave results when this condition is matched. But, what does this actually mean? K is the wave number, which is equal to two pi over the wavelength. The wavelength, in this case, would be the spacial distance between two peaks. So, if we put this definition into our resonance condition equation, we get two pi over lambda, is equal to, times L, is equal to N pi, the pi's cancel out, and we see that the length has to be equal to an integer multiple of half wavelengths. If this length satisfies this condition, then we can have all sorts of standing waves, and the different types of standing waves will be denoted by this integer, N. It'll just mean how many half wavelengths you can fit inside of this tank of water. So, the next thing to do, now that you have information about the wavelength is to determine what the frequency is. To do that, you can just observe, on a stopwatch, how much time it takes for a local minimum to become a local maximum. So, when this standing wave is moving, it's like as if it were rotating. This part will move up and the peaks will move down and become valleys. So, the time it takes for one of these peaks to drop down and back up is equal to one period. So, the period, once you measure that in units of time is going to be equal to one over the frequency. Therefore, frequency is equal to one over that measured period. So, now that you have the wavelength and the frequency information, you can actually calculate what the speed of the water wave would be in this tank. And, that would simply be given as the speed V is equal to the wavelength times the frequency, which is equal to the wavelength divided by the period. My name is Walter Unglaub, and this is "physics labs on the speed of a wave."


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