Essential Ideas in Electronics: Voltage (Part 2)

In this second and final part of our look at voltage, we explore what an electric potential actually is and how a voltage (potential difference) can be created.


Part 1 of this article on voltage introduced the following key ideas:

•    A signal in a system is a voltage
•    A voltage is a difference in electric potential between two places
•    Voltage is formally called potential difference
•    Being a difference measurement, voltage is analogous to height
•    Voltages can be measured with a voltmeter
•    When measuring a voltage, the two voltmeter leads are placed ‘across’ the voltage; that is, to measure the difference in potential between two places the voltmeter leads are attached to these two places.

This second and final part of the article explores what an electric potential actually is and how a voltage (potential difference) can be created.


Fig 1 Inside an atom

You probably know the simple model of an atom that describes it as a positively charged nucleus (centre) surrounded by negatively charged electrons. Overall a complete atom is uncharged because the charge on the nucleus is exactly balanced by the charges on the electrons.

However, if an electron is removed from an atom, it – and the material it is a part of – becomes positively charged. In the same way, the object that holds the removed electron will become negatively charged. There is now a difference in electric charge between the two items.

This difference in electric charge creates a potential difference, or voltage. The size of the voltage is directly proportional to the size of the charge difference. The charge on a electron is tiny, so to create a useful voltage a very large number of charges have to be separated.

The unit of charge is called a Coulomb (C)
and 1C is the charge equivalent to about 6×1018 electrons.
That’s 6 million million million electrons

The charge on a single electron is about
1.6×10-19C, or 0.00000000000000000016C.

The actual voltage created by a particular

charge separation depends on the area over
which the separated charges are spread, the
separation distance and the electrical
properties of the material between the charges.

Fig 2 Separated charges create a voltage

Download complete article Essential ideas: Voltage (3 downloads)