 Now that we have an understanding of voltage and current, we're going to combine these two concepts and talk about power. Power is defined as the amount of energy per second. So the units of power is watts, which is the same thing as joules per second. So for example, if a light bulb produces one joule of light energy each second, then it is a one watt light bulb. A brighter light might produce 100 watts, meaning it's producing 100 joules of light energy per second. So to investigate power in circuits, let's look at a circuit. So in this circuit, let's have a four volt battery and it's supplying two amps, so amp is short for ampere, so two amps of current to a light bulb. Now remember that a volt is just joules per coulomb. So moving one coulomb through a bulb with four volts will deliver four joules of energy. Moving two coulombs through a bulb with four volts would deliver eight joules. Since the current is two amps or two coulombs per second, that means that we're going to produce eight joules of energy per second. But it so happens there is a more general formula for power that we can use in any situation in a circuit. So P equals I times V, where P is the power, I is the current, and V is the voltage. If we think about the units, this makes sense because power is in joules per second, current is in coulombs per second, and voltage is joules per coulomb. So we can see that the joules per second is going to be equal to the coulombs per second times the joules per coulomb. So in our circuit if we wanted to find the power we could use the formula and we would get P is equal to I V, which is equal to two coulombs per second times four joules per coulomb, which is equal to eight joules per second, which is equal to eight watts.