The series circuit rules show how to apply Ohm's law when the circuit has more than one device receiving electrical energy.
The rules will also help us see how the current, the resistance, and the
voltage change in the circuit. Below is an example of a series circuit with 5 electrical components, excluding wires.
The circuit has 1 switch (green), 1 voltage source of 12 volts, and 3
resistors. Notice that the light bulb is also a resistor!
Simply put, the current cannot "make choices" as to where it would go in a series connection. If the current can either go this way or that way, then the circuit is not in series. A circuit that can "make choices" is a parallel connection.
Look carefully at the circuit above and you
will see that the current has to go through the path it is in. This fact
leads us to Rule #1.
This series circuit has 3 resistors. Recall that a load resistor or simply resistor is a device
that resists the flow of current. Does it make sense to you that the
current will be resisted by all 3 resistors? It will indeed!
For example, to find the total resistance for our circuit above, just add 1, 2, and 3.
Let R1 = 1 Ohms, R2 = 2 Ohms, and R3 = 3 Ohms be the resistance in the circuit.
Total resistance = 1 + 2 + 3 = 6 Ohms.
We can now use Ohm's law to find the intensity of the current flowing through the circuit.
Whenever the current goes through a device, a voltage drop or potential
difference occurs because of the resistor in that device. It simply
means that the voltage in that device will not be the same as the
From this, there is an important observation we need to make.
Notice that 12 volts = 2 + 4 + 6Let V be the voltage at the source
The series circuit rules can be summarized and generalized as follow:Let I be the current going through the circuit
Using the same circuit again, we can make the following important observation:
12 volts = 2 volts + 4 volts + 6 volts
12 volts - 2 volts - 4 volts - 6 volts = 0
12 volts + -2 volts + -4 volts + -6 volts = 0
The sum of all 4 voltages around the loop is equal to zero.
In general, this is known as Kirchhoff’s voltage law and it states that the algebraic sum of all voltages around a loop is equal to zero.
Σv = 0
Take the series circuit quiz below to see how well you understand series
circuit. After completing this quiz with 100% accuracy, you will know
exactly how the current, the voltage, and the resistors behave in a
series circuit. You will not need to use a paper and pencil to complete
First, read the lesson about series circuit and then take this quiz.
Objective of the series circuit quiz:
Test your knowledge with the quiz below: