7 junio, 2024

Parallel circuit: concept, characteristics, how to do it, examples

We explain what a parallel circuit is, its characteristics, how to do it and we give several examples.

What is a parallel circuit?

He parallel circuit It is one whose elements are connected through two common points. In this way, the receiving component is subject to the same voltage and acts independently of the other elements.

The following figure shows two small bulbs connected in this way. The current leaves the positive pole of the battery, and when it reaches the bulbs it divides, turning them on.

Then the currents that come out of the bulbs join again and return to the negative pole to start the cycle again. A switch is also visible on the circuit, which is used to turn the circuit on and off at will.

There is an obvious advantage to connecting in parallel: if one of the bulbs burns out, the other is still on. This is because the current needs a closed path to flow. If one bulb burns out, that part of the circuit is left open and current can’t flow there, but you still have a path to the other bulb.

Not only the bulbs (electrical resistors) can be connected in parallel, other elements such as batteries, capacitors, coils and more can also be connected in this way.

Characteristics of parallel circuits

-The elements that receive the current and make use of it, called receiversare at the same voltage as the source or generator.

-The current of the source is divided in each one of the receptors of the circuit and they are added in such a way that, at the end of the journey, the original current returns to the source.

-It is considered that the conductors that join the elements of the circuit lack resistance, however, in practice, the cables do offer a small resistance to the current, which in some cases produces significant effects.

-Each element of the circuit works independently of the others. Since the current has multiple paths to circulate, if any of the components fails, the current does not pass through the damaged element, but is redistributed in the others.

-Parallel circuits are easier to modify, adding or removing elements without having to alter the configuration too much. For the same reason they are easier to repair when a component is damaged.

-Adding resistors in parallel does not increase the total or equivalent resistance of the circuit. In fact, the equivalent resistance in parallel is less than any of the component resistances separately.

-The points of the circuit in which the current is divided, or where several currents converge, are called nodes. In the circuit shown above there are two nodes: the one on the left, where the current coming from the battery is divided, and the one on the right, where the currents coming out of each bulb meet again.

-Each closed portion of the circuit corresponds to a mesh.

Components in Parallel

It is possible to replace a set of elements connected in parallel, by a single component of the same class, called equivalent. The following figure illustrates the symbols used and the resulting configuration:

The formulas to determine the different equivalents are given below:

resistors in parallel

The equivalent resistance of n resistors in parallel is calculated through:

inductors in parallel

The equivalent inductance of n inductors in parallel is calculated in a similar way to resistors, with the formula:

capacitors in parallel

The equivalent capacitance of n capacitors placed in parallel is the sum of the capacities of each one:

batteries in parallel

The voltage of a configuration of identical batteries in parallel is the same of one of them.

How to make a circuit in parallel?

A parallel circuit with 3 resistors is easily assembled with the following materials:

A proto board or support tablet for circuits.
3 commercial resistors.
Connection cables.
Pile or battery.


The support board has holes to insert the terminals of each element. Underneath the board are thin copper lines connecting the dots. The assembly is as shown in the figure:

With the multimeter you can measure the equivalent resistance (the measurement is done by disconnecting the power supply), and also the voltage and current through each element.

Examples of Parallel Circuits

voltage measurement

It is carried out with a voltmeter, which is built into a multimeter. The multimeter is used to measure the most common electrical magnitudes, usually current, voltage and resistance.

To measure the direct voltage or the effective value of the alternating voltage, the voltmeter leads are placed in parallel with the element to be measured.

resistive current divider

It is made with two or more resistances in parallel, fed with a direct or alternate source.

The following figure shows a current divider with two resistors R1 and R2 fed with an ideal voltage source ε. It is precisely the circuit diagram shown at the beginning of the article, where the bulbs are the resistors and the switch is denoted by the letter S:

The current I leaving the battery is divided when it reaches the node, which is the point in green. Current I1 passes through resistor R1 and current I2 flows through resistor R2. Upon reaching the yellow node, both currents join again to form I and continue the cycle.

I1 + I2 = I

Using Ohm’s law, it can be shown that the currents I1 and I2 are:

Batteries connected in parallel

Batteries or cells can be connected in parallel as long as they are of the same voltage, thus increasing the capacity of the set, a measure of how much charge passes through the terminals after one hour when a current of 1 A circulates.

A battery with a capacity of 10 Ah (Ampere-hour), supplies 10 amps in 1 hour, or 1 amp in 10 hours. Since 1 Ah equals 3600 C, this means that the battery has a capacity of 36000 C.

The capacity of the parallel connection is the sum of the individual capacities, very useful to connect more devices. But keep in mind that in practice the life of the batteries is shortened, because they have different internal resistances, even if they are identical and come from the same manufacturer.

The wiring, for its part, also has resistance, which causes current imbalances, so that almost always one of the batteries ends up going through more charge and discharge cycles than the other and deteriorates first.

domestic electricity system

Parallel circuits are essential in the electrical system of buildings, since their main characteristic is that the circuit continues to work, even if a component is damaged.

When a light bulb burns out, for example, the corresponding part of the circuit is left open and no current flows through it. If the appliances were connected in series with the burnt out bulb, they would stop working. Furthermore, the parallel connection of several resistors does not limit the total current supplied by the source.

car light system

The car’s lighting system also consists of parallel circuits, for the reason explained above: if one headlight stops working, the rest of the system still shines.

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