Power's relationship with Ohm's Law

Hey guys,

Today we're going to quickly review power's relationship with Ohm's Law (what we covered last time, V=I*R). Power is what your energy company charges you for, so you might want to pay attention!

We'll add on P = I * V

Where P = Watts (w) of power. One watt is equal to one Joule of energy expended in one second.

Well, what if we only have Voltage and Resistance? What if we only have Current and resistance? How can we solve for the power in a circuit? Ohm's Law (you'll see Ohm's Law a lot)

Since we have V = I*R, then we also have I = V/R (from dividing both sides by R)

Now substitute IR for V, or V/R for I (depending on what we're given to solve for P, and we have two more equations for power:

P = (V^2)/R
P = (I^2)*R

Now it's easy to solve for P if you're only given two of the variables in a circuit.

A great picture can be found at the12volt.com that neatly illustrates the relationship between power, voltage, current, and resistance. Check it out.
http://www.the12volt.com/ohm/ohmslaw.asp