# What is a Parallel Circuit?

## Series Circuit and Parallel Circuit

Electrical circuits may be arranged in two basic configurations called series circuits and parallel circuits. The main difference between the two is that in parallel circuits connect devices or components in branched pathways while while series circuits connect devices in a row one after another.

### Series Circuit

In a **series circuit**, the components are connected to each other in consecutive way one after another in one big loop. In a series circuit, there is only one path through which the electricity is able to flow.

### Parallel Circuit

What is a parallel circuit exactly? Electricians and physicists define a **parallel circuit** as one in which each component is connected in its own branch or loop directly to the source of electricity. When the circuit is closed (with no breaks) this provides multiple different paths through which the electricity is able to flow at the same time. In an open parallel circuit, there is a break somewhere in the pathway, but since each branch is its own independent path, a break in one branch does not effect the devices in another branch. This is shown in Figure 2, which shows a simple parallel circuit.

## Circuits Are Pathways

Going to the airport instills a bit of dread in people, and for good reason! There are long lines, multiple security checkpoints and endless hallways that seem to go on forever. Sometimes you move through the airport effortlessly, while other times it takes forever just to get from one point to another.

A pathway in an airport is much like a **circuit**, which is a path that electrons can flow through. Circuits are very useful - for example, they are the pathways that provide electricity to the appliances, lights and other things in your house.

Circuits come in two basic forms. The first is a **series circuit**, which connects devices in series. This type of circuit provides a single pathway for electron movement. The second type is a **parallel circuit**, which connects devices along branched pathways. This type of circuit provides separate paths for the electrons to flow. We will explore series circuits in detail in another lesson. For now, let's focus on how parallel circuits work to power devices.

## What Does a Parallel Circuit Look Like?

Just what does a parallel circuit look like? The parallel circuit illustration in Figure 3 shows that each component of the electrical circuit is connected from both ends of the component directly to the source of electricity, creating its own loop or branch. Each place where a loop branches off is called a node. The current flows from the electrical or voltage source (V), usually a battery, through the nodes to each component (labeled R for resistor in the diagram) and then back to the source. So some of the current is flowing through all the components at the same time. Because each branch is independent of the others, if there is a break in one of the branches it will not effect the other components of the circuit.

## Properties of Parallel Circuits

There are three important properties of parallel circuits: current, voltage, and resistance.

- In a parallel circuit, the voltage across each component is the same.
- Unlike voltage however, the amount of current that flows through each branch of a parallel circuit is not the same. Current is a measure of the amount of electrons flowing in a circuit. Because each component is in its own loop, when the flow of electricity branches off into different directions at the nodes, the amount of current is divided. After passing through the components, the separated currents rejoin so that the total current is equal to the sum of the current flowing through each branch through each of the components in the parallel circuit.
- Resistance is a property of the components that oppose the flow of electricity. The total resistance in a parallel circuit is actually less than the resistance of the individual components of the circuit. Each additional component diminishes the total resistance of the circuit. This may sound counterintuitive, but it will become more clear later in the lesson.

## Voltage in Parallel Circuits

Voltage is the result of differences in electrical potential energy. This provides the force that causes electricity to move or flow through a circuit. The more electrons there are the greater the electrical potential energy. In a parallel circuit, each component is directly connected to the power sources so the voltage at each component is the same as the source voltage.

## Ohm's Law in a Simple Parallel Circuit

**Ohm's Law** describes the relationship between voltage, current, and resistance. It states that the amount of current is directly proportional to the amount of voltage and inversely proportional to the resistance. Said another way, if the amount of voltage is increased, then the amount of current is also increased or if the amount of voltage is decreased then the amount of current is also decreased. On the other hand, if the amount of resistance is increased the amount of current is decreased. If the amount of resistance is decreased, then the amount of current is increased.

This relationship between current, voltage and resistance is represent by the following mathematical model, or formula:

{eq}I = \frac{V}{R} {/eq}

This formula can be used to calculate the current. If the voltage of a given circuit is 9v and the total resistance is 3, then according to Ohm's Law I = 9/3 or 3 amps

## Resistance in Parallel Circuits

In parallel circuits, resistance diminishes with each added component. This is a result of Ohm's Law. Adding components in parallel increases the number of nodes, or points where the current branches off. So there will be less current flowing through each branch.However total current is the sum of the current through each branch.

{eq}I = I_1+I_2+I_3+... {/eq}

Since Ohm's law says the I = V/R, the total resistance can be written as:

{eq}V=\frac{V}{R_1}+\frac{V}{R_2}+\frac{V}{R_3}+... {/eq}

Factoring out the V from each term on the left gives the following:

{eq}I = V(\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}+...) {/eq}

So the total resistance is {eq}\frac{1}{R} = \frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}+... {/eq}

This information can be used to determine the amount of total resistance and the current for the following parallel circuit:

The voltage in this circuit is 2V. The total resistance is found using the formula from above:

{eq}\frac{1}{R}=\frac{1}{150}+\frac{1}{400}=\frac{1}{0.00916666666} {/eq}

{eq}R=109 {/eq}

Then using Ohm's Law to find current:

{eq}I = \frac{2}{109} = 0.0183A {/eq}

## Lesson Summary

In **parallel circuits**, devices are connected in parallel along branched pathways , while in **series circuits** the are connected all in a row.

- The voltage at each component of a parallel circuit is the same and is equal to the voltage at the source.
- Current is divided among the branches of a parallel circuit.
- If a circuit is closed, then there are no breaks in the circuit path.
- Total current is equal to the sum of the current in each loop.
- Resistance is decreased when circuit branches are added.

**Ohm's Law** describes the relationship between current voltage and resistance. It states that current = voltage/resistance. The current is proportional to the voltage and inversely proportional to the resistance

Unlike series circuits, the devices in a parallel circuit are connected in branches that are independent of each other. This makes parallel circuits more advantageous because the independent branches mean that even if there is a break in one branch, the devices in other branches can continue to operate.

## Branched Pathways

Parallel circuits get their name because the devices along the circuit are connected in parallel. This is like having multiple X-ray screening stations in the same airport terminal. The line initially begins as single-file, but then breaks into multiple, separate lines as you go through your X-ray machine of choice. Others behind you may choose to go through a different X-ray machine, and the number of lines that form depends on how many machines are open. After going through the X-ray machine, everyone merges back together into the same line and continues along the path to their gate.

Just as each X-ray machine line is independent of the others, the devices in a parallel circuit are also independent of each other. Think about it: if the next line over moves more slowly than yours, it has no effect on how quickly or slowly your lines moves. The same is true for parallel circuit branches. And because of this independence, while the total current in the circuit is divided among the parallel branches, the amount of current in each branch is specifically related to the amount of resistance in that branch.

## Circuit Resistance

The **resistance** comes from the device itself and is an opposition to electron movement through the device. Because resistance opposes the movement of current, the amount of current in each branch is inversely proportional to the resistance of that branch.

This makes sense if you think about it. Perhaps the line next to you is moving more slowly because the security officers are manually searching through each individual's carry-on luggage. This resistance slows the movement of the line, making it more difficult for people to move through the screening point and on to their next destination. The same is true for branches in a parallel circuit. The more resistance in an individual branch, the more opposition the current faces as it travels through.

But what's really interesting is that even though each branch is independent, the overall resistance of the circuit depends on the total number of branches present. In fact, as the number of branches is increased, the overall resistance of the circuit is decreased.

Let's go back to the airport to see why this is so. If there were only one X-ray machine open, there would be one long line and everyone would have to move through it. Overall, this would be very inefficient and provide a lot of resistance to the total movement of the people through the security station. But if another X-ray machine opens up, then the line can split into two, and everyone will move through much more quickly. Add yet another X-ray machine, and the 'resistance' decreases even more because people have yet another path they can move through.

The same is true for a parallel circuit. Adding branches is like opening up more X-ray stations in the circuit. The more branches there are, the more pathways for the current to travel through, and this decreases the overall circuit resistance.

## Ohm's Law

We can construct our own simple parallel circuit of two branches, each with a light bulb, connected to the same two points. The battery is also connected to these two points. If each branch is **closed**, meaning that there are no breaks in the circuit path, current will flow from the battery, along each branch, through each device and then back to the battery.

Similar to how a heart pumps blood through your body, the battery produces voltage that 'pumps' current through the circuit. Therefore, more voltage means more current. We also know that like a clogged artery, resistance opposes current, so more resistance means less current.

In fact, this relationship between voltage, current and resistance is summed up in **Ohm's Law**, which states that the current is directly proportional to the voltage across the circuit and inversely proportional to the resistance.

Because each device is connected to the same two points, the voltage across each device is the same. No matter how many branches you add, each will have the same voltage, which is why the light bulbs won't dim as you add more to the circuit! It also means that unlike a string of Christmas tree lights, which are connected in series, if one bulb in the parallel circuit burns out, the others will be unaffected and remain lit.

## Lesson Summary

A **circuit** is a path that electrons can flow through. When electrons move through these pathways, it's like people moving through an airport, navigating the many hallways and security checkpoints throughout the building.

**Parallel circuits** are one basic type of circuit, and these connect devices along branched pathways. In a simple parallel circuit, each branch is connected to the same two points where a battery is also connected. The battery supplies voltage, which, like a heart, 'pumps' current through the circuit. These multiple pathways allow the total current to divide among the branches, but it also means that the voltage across each branch is the same.

The current in each branch depends on the resistance of the device. Current is inversely related to the resistance because **resistance** opposes electron movement through a device. Just like a more thorough screening of each passenger slows down the line of people, greater resistance from a device decreases the current moving through that branch.

Just like the X-ray machines at the airport, each branch in a parallel circuit is independent of the others. This means that what happens in one branch has no effect on the others. However, the overall resistance of the circuit *is* affected by the number of branches. Just like opening up more X-ray machines in an airport, adding branches in a parallel circuit decreases the overall resistance of the circuit itself.

## Learning Outcomes

Reviewing the concepts in this video lesson could allow you to:

- Remember the definition of circuit
- Discuss the structure of a parallel circuit and explain the way in which current moves through a parallel circuit
- Understand the purpose of resistance
- Summarize Ohm's Law

To unlock this lesson you must be a Study.com Member.

Create your account

## Circuits Are Pathways

Going to the airport instills a bit of dread in people, and for good reason! There are long lines, multiple security checkpoints and endless hallways that seem to go on forever. Sometimes you move through the airport effortlessly, while other times it takes forever just to get from one point to another.

A pathway in an airport is much like a **circuit**, which is a path that electrons can flow through. Circuits are very useful - for example, they are the pathways that provide electricity to the appliances, lights and other things in your house.

Circuits come in two basic forms. The first is a **series circuit**, which connects devices in series. This type of circuit provides a single pathway for electron movement. The second type is a **parallel circuit**, which connects devices along branched pathways. This type of circuit provides separate paths for the electrons to flow. We will explore series circuits in detail in another lesson. For now, let's focus on how parallel circuits work to power devices.

## Branched Pathways

Parallel circuits get their name because the devices along the circuit are connected in parallel. This is like having multiple X-ray screening stations in the same airport terminal. The line initially begins as single-file, but then breaks into multiple, separate lines as you go through your X-ray machine of choice. Others behind you may choose to go through a different X-ray machine, and the number of lines that form depends on how many machines are open. After going through the X-ray machine, everyone merges back together into the same line and continues along the path to their gate.

Just as each X-ray machine line is independent of the others, the devices in a parallel circuit are also independent of each other. Think about it: if the next line over moves more slowly than yours, it has no effect on how quickly or slowly your lines moves. The same is true for parallel circuit branches. And because of this independence, while the total current in the circuit is divided among the parallel branches, the amount of current in each branch is specifically related to the amount of resistance in that branch.

## Circuit Resistance

The **resistance** comes from the device itself and is an opposition to electron movement through the device. Because resistance opposes the movement of current, the amount of current in each branch is inversely proportional to the resistance of that branch.

This makes sense if you think about it. Perhaps the line next to you is moving more slowly because the security officers are manually searching through each individual's carry-on luggage. This resistance slows the movement of the line, making it more difficult for people to move through the screening point and on to their next destination. The same is true for branches in a parallel circuit. The more resistance in an individual branch, the more opposition the current faces as it travels through.

But what's really interesting is that even though each branch is independent, the overall resistance of the circuit depends on the total number of branches present. In fact, as the number of branches is increased, the overall resistance of the circuit is decreased.

Let's go back to the airport to see why this is so. If there were only one X-ray machine open, there would be one long line and everyone would have to move through it. Overall, this would be very inefficient and provide a lot of resistance to the total movement of the people through the security station. But if another X-ray machine opens up, then the line can split into two, and everyone will move through much more quickly. Add yet another X-ray machine, and the 'resistance' decreases even more because people have yet another path they can move through.

The same is true for a parallel circuit. Adding branches is like opening up more X-ray stations in the circuit. The more branches there are, the more pathways for the current to travel through, and this decreases the overall circuit resistance.

## Ohm's Law

We can construct our own simple parallel circuit of two branches, each with a light bulb, connected to the same two points. The battery is also connected to these two points. If each branch is **closed**, meaning that there are no breaks in the circuit path, current will flow from the battery, along each branch, through each device and then back to the battery.

Similar to how a heart pumps blood through your body, the battery produces voltage that 'pumps' current through the circuit. Therefore, more voltage means more current. We also know that like a clogged artery, resistance opposes current, so more resistance means less current.

In fact, this relationship between voltage, current and resistance is summed up in **Ohm's Law**, which states that the current is directly proportional to the voltage across the circuit and inversely proportional to the resistance.

Because each device is connected to the same two points, the voltage across each device is the same. No matter how many branches you add, each will have the same voltage, which is why the light bulbs won't dim as you add more to the circuit! It also means that unlike a string of Christmas tree lights, which are connected in series, if one bulb in the parallel circuit burns out, the others will be unaffected and remain lit.

## Lesson Summary

A **circuit** is a path that electrons can flow through. When electrons move through these pathways, it's like people moving through an airport, navigating the many hallways and security checkpoints throughout the building.

**Parallel circuits** are one basic type of circuit, and these connect devices along branched pathways. In a simple parallel circuit, each branch is connected to the same two points where a battery is also connected. The battery supplies voltage, which, like a heart, 'pumps' current through the circuit. These multiple pathways allow the total current to divide among the branches, but it also means that the voltage across each branch is the same.

The current in each branch depends on the resistance of the device. Current is inversely related to the resistance because **resistance** opposes electron movement through a device. Just like a more thorough screening of each passenger slows down the line of people, greater resistance from a device decreases the current moving through that branch.

Just like the X-ray machines at the airport, each branch in a parallel circuit is independent of the others. This means that what happens in one branch has no effect on the others. However, the overall resistance of the circuit *is* affected by the number of branches. Just like opening up more X-ray machines in an airport, adding branches in a parallel circuit decreases the overall resistance of the circuit itself.

## Learning Outcomes

Reviewing the concepts in this video lesson could allow you to:

- Remember the definition of circuit
- Discuss the structure of a parallel circuit and explain the way in which current moves through a parallel circuit
- Understand the purpose of resistance
- Summarize Ohm's Law

To unlock this lesson you must be a Study.com Member.

Create your account

#### How do you know if a circuit is parallel or series?

You can determine if a circuit is a parallel or series circuit by looking at connections and components. If both ends of each component are connected directly to the battery or source of electricity with no other component in between, then it is a parallel circuit.

#### What is the difference between series and parallel circuits?

In a series circuit, each component of the circuit does not connect directly to the batter. In a parallel circuit, each component of the circuit is connected directly to the battery or power source.

#### What is the current in a parallel circuit?

The current in an electrical circuit is the flow of electricity. In a parallel circuit the total current is the sum of each branch or loop of the circuit.

#### What is a parallel circuit and how does it work?

A parallel circuit is one in which both ends of each component are connected directly to the battery or source of electricity with no other component in between. Electricity flows from the source directly to each component. If the portion of the circuit to one component is broken, the other components still have complete circuits and can still operate.

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