When a resistor is connected to a circuit, that connection can be either series or parallel. Let us now know what will happen to the total current, voltage, and resistance values if they are connected in series or in parallel.

A resistor is a passive two-terminal electronic component that applies electronic resistance as a circuit element. Resistors reduce current flow and lower voltage levels within the circuit. Most circuits often have more than one resistor to limit the flow of charges in a circuit. There are two simplest combinations of resistors series and parallel.

### Components of Circuit

A circuit is made up of a conductor (wire), power source, load, resistor, and switch. A circuit starts and ends at the same point. Usually, copper wire without insulation is used as a conductor. A switch is used to make or break a circuit. Resistors control the flow of electric current in the circuit. A resistor is a passive element which means that it only consumes power but does not generate power. A load in a circuit consumes electrical energy and converts it into other forms of energy such as light, heat, etc. A load can be a light bulb, fan, etc.

**Need for a Combinational Circuit**

In an electronic circuit, different components are connected either in series or in parallel to form various resistive networks. In the same circuit, resistors can sometimes be connected in different loops in parallel and in series to form more complex resistive networks. These circuits are known as mixed resistive circuits. However, in the end, the total resistance must be known. It is important to know how to do this because resistors never exist in isolation. They are always part of a larger circuit that will have many resistors connected in different combinations. So how do we calculate this total resistance for resistors in series and parallel circuits? In the next section, let’s look at how to find the total resistance for resistors in series and parallel combinations.

## Resistors in Series

Two or more resistors are connected in series when the same quantity of current flows through all the resistors. In such a circuit, the voltage across each resistor is different. In a series connection, if any resistor breaks or faults, the entire circuit is closed. The construction of a series circuit is simpler as compared to the parallel circuit.

When some resistors are connected in series. Consider three resistors with different values:

**Resistance**

The total resistance of a circuit with series resistors is equal to the sum of the individual resistors. This means, in the above figure there are three resistors whose values are 1KΩ, 5KΩ, and 9KΩ respectively.

The total resistance value of the resistive network is −

which means 1 + 5 + 9 = 15KΩ total resistance.

Where R_{1} is the resistance of the first resistor, R_{2} is the resistance of the second resistor, and R_{3} is the resistance of the third resistor in the above resistor network.

**Voltage**

The total voltage seen in a series resistor network is the sum of the voltage drops at each individual resistance. In the above figure, we have three different resistors which have three different values of voltage drops across each phase.

The total voltage is seen in the circuit −

which means 1v + 5v + 9v = 15v is the total voltage.

Where V1 is the voltage drop of the first resistor, V2 is the voltage drop of the second resistor and V3 is the voltage drop of the 3rd resistor in the above resistor network.

**Current**

The total amount of current flowing through a set of resistors connected in series is the same at all points throughout the resistor network. So when measured at the input or at any point between the resistors or even at the output the current is the same 5A.

According to Ohm’s Law: I = V/R

This means that the current at all points is 5A.

Where I_{1} is the current through the first resistor, I_{2} is the current through the second resistor and I_{3} is the current through the third resistor in the above resistor network.

## Resistors in Parallel

Two or more resistors are connected in parallel when the voltage across all the resistors is the same. In this type of circuit, when the branches meet at a common point, the current is drawn out and reconnected. A resistor or any other component can be easily connected or disconnected without affecting other elements in a parallel circuit.

When some resistors are connected in parallel. Consider three resistors with different values:

#### Resistance, Voltage, and Current

The total resistance of a circuit with parallel resistors is calculated differently from the series resistor network method. Here, the reciprocal value of the individual resistors is added with the inverse of the algebraic sum to obtain the total resistance value.

The total resistance value of the resistive network is −

Where R_{1} is the resistance of the first resistor, R_{2} is the resistance of the second resistor, and R_{3} is the resistance of the third resistor in the above resistor network.

If R_{1} = 10KΩ, R_{2} = 2KΩ, and R_{3} = 1KΩ. The total resistance of a parallel resistive network will be –

**The total voltage seen across a network of parallel resistors is the same as the voltage drop across each individual resistance.**

The initial voltage is 9 volts that will be encountered across all resistor terminals.

**The total amount of current entering a parallel resistive network is the sum of all individual currents flowing in all parallel branches. The resistance value of each branch determines the value of the current flowing through it. The total current through the network is**

Because Total current, **I = V/R**

According to Ohm’s Law Total Resistance, R = V/I

A resistor is used especially as a load at the output of many circuits. If a resistive load is not used, a resistor is placed before the load. The resistor is usually a basic component in any circuit.