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Series vs Parallel | A Comparison of Series and Parallel Circuits

There are three basic types of Electric Circuits: Series, Parallel and a Combination. Understanding these circuit configurations will help you in analyzing the circuits and with aid of couple of fundamental rules, you can easily calculate the current and voltage of each and every component. So, in this guide, let us take a closer look at the basics of Series and Parallel Circuits, compare Series vs Parallel and also list out some applications of Series and Parallel Circuits.

What is a Series Circuit?

A simple DC Circuit consists of a closed path in which the direct current flows. The simplest source of DC is a battery and if we connect a small lamp across the terminals of the battery, then it makes up a simple DC Circuit.

But practical circuits consist of more components than a single lamp. If a circuit consists of more than one component and if they are all connected end-to-end so that the same current flows through all of them, then the circuit is known as a Series Circuit.

If we take the simplest electrical component i.e., a Resistor as an example, then the following circuit shows three resistors connected in Series with the voltage source. There is only one path for the current to flow in a series circuit.


Since current is same in all the resistors, we can easily calculate the voltage across the individual resistors using Ohm’s Law.

If V is the supply voltage, I is the current in the circuit, R1, R2, R3 are the resistances and VR1, VR2 and VR3 are the voltages across the respective resistors, then applying Ohm’s Law, we get.

VR1 = I x R1, VR2 = I x R2 and VR3 = I x R3

V = VR1 + VR2 + VR3 = IR1 + IR2 + IR3

If R is total resistance of the circuit, then V = IR and hence

IR = IR1 + IR2 + IR3

R = R1 + R2 + R3

So, the total resistance of a series resistor circuit is equal to the sum of individual resistances.

Voltage Divider

From the above explanation of series circuit, you might have noticed an interesting point about voltages across the individual resistors. Let us simplify this discussion by considering just two resistors in series.


Here, V is the supply voltage, R1 and R2 are the resistors and VR1 and VR2 are the voltages across R1 and R2 respectively.

From Ohm’s Law

V = IR = VR1 + VR2 = IR1 + IR2

If we calculate the voltage across R2, we get

VR2 = V * R2 / (R1 + R2)

The voltage across R2 is a portion of the input voltage. This is known as a Voltage Divider Circuit or Potential Divider Circuit.

Kirchhoff’s Voltage Law (KVL)

From the previous Series Circuit consisting of three resistors, we have established that source voltage is equal to the sum of voltages across the individual resistors.

V = VR1 + VR2 + VR3

Rearranging this equation, we get the Kirchhoff’s Voltage Law.

V – VR1 – VR2 – VR3 = 0

According to Kirchhoff’s Voltage Law (KVL), the algebraic sum of voltages in a closed loop is equal to zero.

Application of Series Circuit

One of the best-known application of Series Circuit are our Series Holiday Lights. During Christmas and holiday season, we decorate our homes with colorful lights that comprises on a number of lamps all connected in series.


The main problem with these series holiday lights is that even if one bulb goes out, it interrupts the flow of current and the whole series will not light up.

What is a Parallel Circuit?

In a series circuit, there is only one path for the current to flow. Coming to the parallel circuit, there will be more than one path for current flow. If we take three resistors once again, then the following images shows different configurations of three circuit elements connected in parallel.


The circuits in the above image might look different but actually they are essentially the same. If you look closely, one end of all the circuit elements (resistors in this case) is common and also the other end. So, a parallel circuit of two elements consists of two common points.

To understand more about parallel circuits, consider the following circuit in which we have three resistors connected in parallel to the voltage source. As all the three resistors are connected across the voltage source, the voltage is same for all the resistors.


But the same is not true for current as it has multiple paths to flow. If I is the total current and IR1, IR2 and IR3 are the currents flowing through respective resistors, then total current is equal to the sum of individual currents.

I = IR1 + IR2 + IR3

Applying Ohm’s Law, we get IR1 = V / R1, IR2 = V / R2 and IR3 = V / R3

If R is the total resistance of the circuit, I = V / R. Using all these in the above equation, we get

V / R = V / R1 + V / R2 + V / R3

So, 1/R = 1/R1 + 1/R2 + 1/R3

For resistors connected in parallel, the inverse of the total resistance is equal to the sum of inverse of individual resistances.

Kirchhoff’s Current Law (KCL)

From the above discussion we have the total current in the circuit as the sum of individual currents in the respective resistors.

I = IR1 + IR2 + IR3

We can rearrange the above equation and get the Kirchhoff’s Current Law.

I – IR1 – IR2 – IR3 = 0.

According to Kirchhoff’s Current Law (KCL), the algebraic sum of currents entering a node and leaving a node is equal to zero.

Current Divider Circuit

Just like a series circuit of resistors can be configured as a Voltage Divider Circuit, the parallel circuit of resistors can lead to a Current Divider Circuit.

While the voltage divider is quite popular, the usage of current divider is application dependent.

Application of Parallel Circuit

An important application of parallel circuit is our home electrical wiring. The basic wiring in all homes is actually a parallel configuration. In this way, all the parallel branches receive the full 120V (or 240V) while the current is dependent on the load.


Even if there is a problem/fault with one parallel branch or circuit, only the appliances or devices connected to that circuit get affected while the remaining branches operate normally.

Series vs Parallel Circuits: Comparison

The following table shows a simple comparison of Series vs Parallel Circuits.

Series Circuit Parallel Circuit
In a series circuit, same current flows through all the components. In a parallel circuit, the current can have more than one path.
All the components are connected in an end-to-end fashion with only one common point between the components. One end of all the components in a parallel is connected to a common point and the other end to another common point. So, parallel circuit has two common points.
Voltage across the components is not the same and is dependent on the individual resistance. Voltage across all the components in a parallel circuit is same and is equal to the supply voltage.
If one component fails in a series circuit, then the entire circuit stops functioning as there is only one current path. Even if one of the parallel branches fail, the rest of the branches continue to work normally.
The current is same in all the components and the sum of individual voltages is equal to the supply voltage. The voltage is same across all the components in parallel and the sum of individual currents is equal to the total current in the circuit.
If we have three resistors connected in series, then the equivalent resistance is the sum of individual resistances (R = R1 + R2 + R3). If we connected three resistors in parallel, then the inverse of the equivalent resistance is equal to the sum of the inverse of individual resistances (1/R = 1/R1 + 1/R2 + 1/R3)
Holiday Serial Lights are an example of Series Circuit. Residential Electrical Wiring is implanted as a Parallel Configuration.


Series and Parallel Circuits are two of the basic forms of electric circuits. A clear understanding of these two circuits will help you analyze any complex circuit with ease. We learned the basics of Series Circuit, Parallel Circuit, a comparison of Series vs Parallel Circuits and also some applications.

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