Phase differences in physics will likely be measured by revolutions. Find out about phase difference in physics with help from an applied physics professional in this free video clip.

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Phase differences in physics will likely be measured by revolutions. Find out about phase difference in physics with help from an applied physics professional in this free video clip.

Part of the Video Series: Such Great Physics

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Hello. My name is Walter Unglaub and this is phase difference in physics. So here I have a plot of 2 oscillatory functions that oscillate in time and you could probably recognize this one as sine where it starts at zero, increases and then decreases and completes one revolution. And if time is measured in radiance this would be 2Pi and this point right here of course the first intersection, would be half of that. So just Pi. And let's say I have a different signal that is offset. So if we compare the peaks we see that there is a phase difference. They're not in phase, they're out of phase. So how can we describe this mathematically. Well, Y1 which is my sine function would simply be A times sine Omega T. Here A is the amplitude, Omega is the angular frequency but here I'm assuming Omega to simply be equal to 1. So I have sine in terms of just time. Now my second function I can write, assuming that it's the same amplitude, as A sine, Omega T plus a phase difference. Plus because the phase difference of this second signal is offset to the left of the original signal. If it was offset to the right then I would be writing minus Phi. Now we can see that Phi has to be given in terms of the angular frequency Omega, and this change in time, this difference in time between the 2 peaks. So our phase difference will be equal to Omega, Delta T. But if we know Omega in this particular case is equal to 1 because I'm using units of radiance for time, then my phase difference will simply be equal to the change in time. So what is this difference? Well, it's equal to this difference; the difference between when the rising slopes intersect with the T axis. So if this is 2Pi and this is Pi, right in the middle is 3Pi over 2. So Delta T is equal to 2Pi or 4 Pi over 2 minus 3Pi over 2 which is equal to simply Pi over 2. That would be my phase difference. Now I can understand in the unit circle why co-sine which is the horizontal component is separated in angle by 90 degrees or Pi over 2 from sine which is the vertical component. It's all due to this phase difference between a sine function and in this case what turned out to be a co-sine function. So co-sine is simple sine but with an added phase difference that is equal to Pi over 2. And this is very useful in understanding how separated two signals are in time or in space if you plot the signals with respect to space. My name is Walter Unglaub and this is phase difference in physics.