Series Resistors

Series resistors are resistors connected in a way that the current can only follow one path, while parallel resistors allow the current to take more than one path. You can see an example of resistors connected in series in figure 1.

Image of a closed circuit. The circuit has a rectangle shape. On the inferior base, there is the battery with its negative and positive poles and labelled V zero. On the right side of the rectangle, there are two resistors, R 1 and R 2. They are both drawn as zigzag lines.

Figure 1. Resistors connected in series.

In resistors connected in series the charge and energy are preserved (as in any other circuit). Current and Voltage behave differently in series resistors when compared to parallel resistors. Let's use figure 1 as an example.


If we consider current (Amperes) as the number of electrons that are passing through a certain point of the circuit in a given time (Coulombs per second), and the electricity can only follow one path, that means that the current will be the same in all points of the circuit (R1 and R2), since electrons cannot just disappear.


Voltage behaves differently than current. Voltage is the energy contained in each Coulomb of charge. When the electricity passes through resistor 1 (R1) some energy is drawn by this component, so the voltage reaching resistor 2 (R2) is lower. For example, if the battery is providing 12 volts and R1 is drawing 4 volts, R2 will receive 8 volts.

Equivalent Resistor

An equivalent resistor is a resistor that will have the same effect on the circuit as the resistors already in the circuit (R1 + R2 in this case). To calculate the equivalent resistor for resistors in series, you simply need to add up the resistances of both resistors.