Understand Current and Potential Difference in Series Circuits

Here is an example of a simple series circuit. 

How does the current vary in series circuits? What happens to the potential difference in these circuits? Let's find out!

First, we will remind ourselves of some important key terms.

Current - In a circuit, the current is the rate of flow of charge. Electrons move through the wires and components - a higher current would mean more electrons passing through a point every second. Current is measured in Amps (A) with an ammeter. 

Potential difference - In a circuit, the potential difference is a measure of the electrical energy transferred. Cells and batteries provide a potential difference, and that potential difference is used by the components. Potential difference is measured in Volts (V) with a voltmeter. 

Series circuit - In a series circuit, all the components are connected in one continuous loop, one after another. 

So, what if we used ammeters and voltmeters to measure current and potential difference in series circuits? What sorts of observations would we make?

Current in series

In this series circuit, the current flows from the positive terminal of the cell. It travels in a loop and returns to the cell. 

Imagine placing three ammeters in series in this circuit. The current in each of the ammeters would be the same. 

Current is always constant in a series circuit or loop. 

Why? Because current doesn't get split or used up. It follows the loop and returns to the cell or battery. Remember, current is the rate of flow of charge. In series, the rate of flow of charge stays constant.

So, if the current at the ammeter closest to the cell was measured as 1.5 A, the current would be 1.5 A at the other ammeters too. 

Potential difference in series

The first thing to remember is that to use a voltmeter, we must put it in its own loop. If we don't do this, it won't work. Here is an example. 

In this circuit, there are three voltmeters. Voltmeter A measures the potential difference provided by the cell. Voltmeters B and C measure the potential difference transferred at each of the bulbs. 

In this case, the potential difference measured at A would be equal to the sum of the potential difference at B and C. 

Potential difference is shared in a series loop. 

Why? Because potential difference is a measure of the electrical energy transferred. The bulbs in the circuit use that electrical energy and convert it into light and heat energy. The energy gets 'used up'. 

Let's imagine that the cell provided a potential difference of 6 V, measured by voltmeter A. The bulbs are identical. In this case, voltmeters B and C would each measure a potential difference of 3 V. 

Potential difference gets shared equally if the components are identical. If one of the components has a higher resistance, it will take a bigger share of the potential difference. 

Now let's try some questions!