# Our Objective

How to determine the equivalent resistance of two resistors when connected in series.

# The Theory

Before we start learning about series circuits, we need to know what electrical circuits are and what are different types of circuits!

## Electrical Circuit

An electric circuit is simply a closed loop through which charges can continuously move. An electric circuit basically contains a source of electricity, a load resistance, a switch or a key for turning the circuit on or off at one's convenience.

The diagrammatic representation of an electric circuit is called the circuit diagram.

## Types of circuits

When two or more resistors are connected such a way that one end of one resistor is connected to the starting end of the other, then the circuit is called a **Series Circuit**

Similarly, if the starting ends of two resistors are joined to a point and the terminal ends of the two are combined and given connection to a source of electricity,

those circuits are called** Parallel Circuit.**

Since the current has only one path to take, the current through a series circuit is the same through each resistor.

## Before calculating the equivalent resistance, let me ask you, "What is resistance?"

Voltage can be thought of as the pressure pushing charges along a conductor.

Electrical resistance shows how much energy you need when you move the charges/current through your devices. If you need lots of energy, then the resistance required is also high.

In many materials, the voltage and resistance are connected by Ohm's Law:

That is, the property of a conductor to oppose the flow of charges through it is called its resistance.

It is measured as resistance,

All metals are good conductors, so all metal wires have a relatively low resistance.

The longer a piece of wire the higher is its resistance. Double the length means double the resistance.

ie.,

The resistance of a piece of wire also depends on its thickness/cross-sectional area A of the conductor. Double the area means half the resistance. A thin wire has a higher resistance than the same thick piece.

ie.,

Finally, resistance of a piece of wire depends on its temperature also. The higher the temperature the higher is the resistance.

## Calculating the effective resistance/total resistance of series circuits:

The total resistance/effective resistance of the circuit is found by simply adding up the resistance values of the individual resistors. Adding resistors in series always increases the effective resistance.

ie., If R_{s} be the resistance of the series combination then,

Here, we used Meter Bridge to calculate the effective resistance accurately.

The Meter Bridge is a device for measurement of resistance using the principle of Wheatstone Network.

Let’s do an experiment now ……