 We can actually combine the equations for power, as well as the equations for Ohm's law, to give us a few different ways to calculate the power in an electrical circuit. I want to start here by reminding you of what the equation for power was for an electrical circuit, and it was the current times the voltage. Now in Ohm's law we have a couple of different formats we have. So for example, the voltage could be written as the current times the resistance, and the current can be written as the voltage divided by the resistance. If I plug those in to this power equation, plugging in first the voltage is equal to the current times the resistance, that means I'll actually have current in there twice, and it will be the current squared times the resistance. So if you know the current and the resistance, you can either use that to find the voltage and use our original power equation, or you can use this alternate equation. Similarly, if you know the voltage and the resistance, you can either find the current and then use that in your original power equation, or substitute it in so that it's the voltage squared divided by the resistance. Now just to show that all of these equations actually work out the same, let's consider a case where you've got a current of 1.25 amps, a resistance of 4 ohms, and a voltage of 5 volts. This is the same as the examples I used in my earlier Ohm's law. We're going to take a look at what this would do for each one of our cases. For my original equation for power, I would plug in my current and my voltage, and I'd find I've got 6.25 watts, if I had 1.25 amps, times 5.00 volts. If I use the current and the resistance, excuse me, let me re-copy this one, plugging in the current squared and the resistance, you plug in the 1.25 squared times the 4 ohms, and you'll still get 6.25. Now notice that amp squared times ohms, if you work out all the units, will also give you watts. And then my last example here, plugging in, if I've got the voltage and the resistance, the voltage squared divided by the resistance is going to give me the same one as well. So this also tells you that a volt squared divided by an ohm must be equal to a watt. So this is how you can use both Ohm's law and the power rule for an electrical circuit to be able to calculate the power for all three situations.