Hey guys. In this video, we're going to talk about power in AC circuits. What elements are emitting power? What elements are not emitting power? What the average power is, and things like that. Alright? Let's get to it.
In AC circuits, the only element to have an average power not equal to 0 is? What do you guys think it is? It's the resistor. This is because whatever energy enters a capacitor or an inductor equals the energy that leaves it. Capacitors and inductors are elements that store energy. A capacitor stores charge to store electric potential energy, and an inductor stores its current to store magnetic potential energy. Okay, but either way, they only store energy. The resistor is what's actually bleeding the energy from the circuit. Okay? So if you were to plot the other elements' power as a function average, all the peaks would cancel all the valleys, and you would have no power on average. Okay? The maximum power of a resistor is going to be that maximum voltage across the resistor times the maximum current. Okay?
Now, as a function of time, you can say that the power equals the current as a function of time squared times the resistance. This gives us the following graph of power and current versus time. You can see that current, like we expect, is going to have no average value because anything that's positive, any peak above the horizontal cancels with the negative peaks below the horizontal, but power stays above the horizontal. It just bounces above the horizontal. So it's always positive and therefore it has nothing to cancel it out. So, on average, it is absolutely not 0. Okay?
The average power emitted by an AC circuit is going to be one-half of the maximum power. This is because the power's peaks are completely symmetric. So the average is going to be one-half of the maximum. So it's going to be one-half
Let's do a quick example. An AC source operating at a maximum voltage of 120 volts is connected to a 10 ohm resistor. What is the average power emitted by this circuit? Is it equivalent to the RMS power, which would be
Alright guys, that wraps up our discussion on power in AC circuits. Thanks for watching.