 All right, now we know what resistance is. I can show you Ohm's law. So Ohm's law is V equals IR, or the voltage is equal to the current times the resistance. This means if we were to look at any circuit, if we knew any of the two quantities, so voltage, current, and resistance, then we could calculate the third. So batteries and other power sources usually output a particular voltage. So for example, we could have a 9-volt battery. Resistors are components which have a particular resistance that does not change. Let's suppose that this resistor has a resistance of 100 Ohms. So then we could use Ohm's law to calculate the current that flows through this circuit. So let's give it a go. So we need to rearrange our equation for the current, which is I. So let's go. So I got that just by dividing both sides by the resistance. Then all I need to do is substitute in the numbers to find the current. So there we go. 9 volts divided by 100 Ohms gives us 0.09 amps. And that's how you use Ohm's law.