In a series circuit, current flows to each component in turn. There is only one path it can take, and all the electrons flow at the same rate. Current is the same everywhere. In a series circuit with resistors in it, the total resistance is the sum of all of the individual resistances.
For example, imagine a circuit with three resistors, each of 4 ohms - powered by a 12 volt battery. Total resistance is 12 ohms, and Ohm's law says there is 1 ampere of current flowing through the whole circuit.
However, the voltage at different points changes, as the electromotive force or pressure, drops from a potential difference of 12 volts as it leaves the battery, to virtually no difference, no voltage at all, as it returns.
This is called voltage drop. It is caused by the pressure lost in driving the current through the resistor.
After the first resistor, voltage has dropped from 12 to 8 volts. After the second, it’s down to 4 volts. After the third, zero.
The voltage drop across each resistor can be found by subtracting the voltage after a resistor, from the voltage before it - or the difference can be measured. The voltmeter will read 4 volts in each case, because that’s the difference between the 2 points, the potential difference, or voltage.
Ohm’s law can be used in series circuits to calculate voltage, resistance and current. Any one of these can be calculated as long as the values of the other two are known.
Source: CDX Global
