In a series circuit all load elements are placed one after the other. Current has only one way to flow since there are no branches. Furthermore, current is the same everywhere in the circuit. Voltage, however, will slowly drop in each subsequent element. Here’s how it works.
The circuit below has three identical resistors in series. Current flows from the positive terminal of the battery to the negative terminal. When it passes a resistor the voltage decreases by a third.
We can easily calculate this “voltage drop” by using Ohms Law. But first, we need to know the current drawn by the circuit. To do that we need the total resistance of the circuit. We can find this by adding up all the resistor values.
So this total resistance of 3k Ohm can be used to calculate the current by using Ohm’s law.
Voltage drop across resistors
But what about the amount of voltage across each resistor? We can use Ohm’s law for that as well. We only need to take the total resistance into account. Here is how to calculate the voltage drop across the first resistor.
The same goes for the other resistors in the circuit. Since they all have the same values here, the voltage drop is the same for all of them.