Why Do Parallel Resistors Have Less Resistance?

Why Do Parallel Resistors Have Less Resistance? | howtoimprovehome.com

Electric Circuits can be connected in two different ways, series connection and parallel connection. However, when the circuit is connected parallel, it has less resistance. Even if the two circuits have identical resistors, the parallel one will have less resistance.

Why do parallel resistors have less resistance?

Because in a parallel connection, the total resistance is the summation of the reciprocal of each resistor. This means that the total resistance will be less than the smallest resistor found in the parallel connection. So the current entering the connection becomes larger.

In the rest of this article, I’ll discuss how the parallel connection works, what are the components of an electric circuit, the difference between parallel and series connections, why a parallel connection has less resistance than a series one, which connection is better to use, and why.

Why Parallel Connection Has Less Resistance?

The parallel connection has less resistance than the series one, which is due to the way of connecting the resistors. In the series connection, the resistors are connected in a row, resulting in a total resistance larger than any resistor of them. Since the total resistance in series connection is Reff = R1+ R2.

The parallel connection has less resistance because its total resistance isn’t equal to the summation of each resistor resistance. The total resistance equals the summation of each resistor resistance reciprocal Reff = 1/R1+1/R2. This means the total resistance is less than the least resistor.

How are Parallel Resistors Constructed?

In a parallel connection, the resistors have the same starting node and ending node. This means the current entering the first resistor differs from the one entering the second resistor unless the two resistors have the same resistance.

Each resistor is connected in its own branch; there is no resistor after or before it. Then the resistance can’t be the summation of each branch resistance because they are connected in different branches. So to determine the total resistance, I have to use a physical equation.

The general equation of resistance is R=V/I. The total current is the summation of each current entering each resistor Itot = I1+I2. If each I is removed and substituted from the equation Itot=V(1/R1+1/R2), Then Reff = 1/R1+1/R2. And in the end, the Reff is less than the least resistor in the circuit.

What Is the Difference Between the Parallel and Series Connections?

The parallel connection depends on all the resistors being connected separately in different branches. But all the resistors have the same starting and ending point. Meanwhile, the voltage is constant across the connection. The current intensity is different in each resistor.

The series connection is different; all the resistors are connected in a row each resistor is followed by another. And this means that the current passing any resistor is the same, but it’s not the same on the voltage side. Since V= IR, the voltage across each resistor depends on its resistance.

Which Connection Is Better Parallel or Series?

The parallel connection is better than the series one because the total resistance in the parallel connection is always smaller than the resistance of the series connection. But what are the advantages of having small resistance?.

Advantages of Parallel Connection

  1. The voltage V is constant across each resistor in the circuit. This means that if you have several lamps connected in a parallel way, each lamp will shine the same way, and the number of connected lamps doesn’t matter. Increasing the number of lamps won’t affect the voltage.
  2. Each resistor is connected to a different branch. This means that if any resistor is damaged or turned off, then the whole circuit will continue to operate finely. So you can switch off any resistor, and the other still runs.

Disadvantages of Series Connection

  1. The voltage isn’t constant across each resistor in the circuit. This means if you have several lamps connected in a series way, the first lamp will shine the most, and the brightness will continue to decrease till the last lamp. Increasing the number of lamps affects the voltage.
  2. Each resistor is connected, followed by another resistor. This means if any resistor is damaged or turned off, the circuit becomes open, and no current will pass to the other resistors. So you can’t switch off any resistor, and the other still operates.

Where Are Parallel and Series Connections Used?

A parallel connection can be used in different places:

  • Homes
  • Offices
  • Infrastructure
  • Devices
  • Lighting fixtures

A series connection uses are limited, but it’s used in some devices:

  • Water heaters
  • Freezers
  • Refrigerators
  • Well water pump

How To Decrease Resistance in Series or Parallel Connections?

To decrease resistance, you have first to understand what resistance depends on. The resistance can be calculated through two equations:

  • Ohm’s law: R=V/I
  • R= ρ*L/A

In Ohm’s law, the resistance R is inversely proportional to the current intensity I, but it’s not an affecting factor. This means that if you increase the current intensity, the resistance won’t decrease. You can imagine it that way, you have a road full of obstacles, and ten cars are passing through the road. 

If the number of cars passing through the road increases, do the obstacles decrease? The answer is NoIt’s the same with current and resistance; increasing the current won’t affect the resistance. The resistance R is not affected by current intensity I.

The second equation is the correct equation to use; it’s more concerned about the road itself. The ρ is not so important now. The two factors that matter are the length of the wire and the cross-sectional area of the wire A because the ρ depends on the material of the wire.

From the equation, increasing the length of wire will increase the resistance, while increasing the cross-sectional area will decrease the resistance. This rule can be followed in either of the two connections, whether it’s a parallel connection or a series connection.

What Are the Components of an Electric Circuit?

Every application we use is made of an electric circuit. Electric circuits are simple structures; they consist of three main components. The first component is the source of electricity, for example, the battery. The other two components are the conducting material and the device.

The Source of Electricity

It’s an essential component in the circuit. The electricity is generated through the movement of the electrons from the positive terminal to the negative terminal. The movement of electrons is forced out due to a force called the potential difference P.d. The source has many examples:

  • Battery 
  • Solar Cell
  • Hydroelectric plant

The Conducting Material

The electrons need a material to move from the positive to the negative terminal. However, there is a disadvantage to the conducting material. Each material consists of electrons and atoms; they collide with the electrons passing. And it results in losing some of the energy of the electrons as heat.

The Device in The Circuit

It’s the component that needs electricity to operate. In general, it can be any device connected to a wall socket, for example, the television. The television is considered a device connected to a circuit. The device uses the electric current that results from the movement of the electrons to operate.

Other Components in The Circuit

The electric circuit can include other components. One of these components is the key. The key is used to switch the circuit on or off. The key does that by either making the circuit open (switching off); so no current can flow through the circuit.

The key can also make the circuit closed (switching on); the current can pass through the circuit to the device to operate it. You can find the key in many things you use daily, the lights in the rooms, the power button in our devices, and many other devices.

The circuits can experience unexpected high currents; as a result, the circuit may overload and lead to a fire. Another component is used in the circuit to deal with these high currents; this component is the fuse. Its job is to be burned instead of the electric circuit.

Types of Electric Circuits

The electric circuits mainly have two types, series circuits, and parallel circuits.

  • Series circuits
    A series circuit is constructed of a row of devices; each device is connected after the other. This arrangement results in a different potential difference P.d across each device, and this inconstancy has many disadvantages.
  • Parallel circuits
    A parallel circuit is constructed differently; each device is connected to a separate branch. This way of connection results in a constant potential difference P.d, but the inconstancy here is in the current each device receives.


To summarize, parallel resistors have less resistance, and this is due to the way they are connected. The total resistance in parallel resistors is less than the least resistor. While the current is divided between all the resistors, the voltage is across each resistor is constant.

This makes the parallel connection is better than the series connection, and the parallel connection is being used in many different places, including houses, offices, and lightning fixtures.

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