Home - Education Resources - Science of NDT - Electricity


After reading this section you will be able to do the following:

  • Explain how a circuit is formed.
  • List examples of sources that the voltage for any electrical circuit can come from.
  • Compare the differences between kinetic and potential energy.
  • Discuss what would happen if a resistor was not included in a circuit.

When we connect various components together with wires, we create an electric circuit. The electrons must have a voltage source to create their movement and, of course, they need a path in which to travel. This path must be complete from the EMF source, through the other components and then back to the EMF source.

The voltage for any electric circuit can come from many different sources. Some common examples are: batteries, power plants, fuel cells.

Power Plant Flash Light Battery
Car Battery Fuel Cell

When we plug an appliance into a wall outlet, voltage and current are available to us. That voltage is actually created in a power plant somewhere else and then delivered to your house by the power wires that are on poles or buried underground.

As a matter of fact, since no current can flow unless there is a voltage source, we also refer to these sources as current sources. In other words, without the voltage source, there will be no current flowing. This makes it a current source instead of a voltage source.

Batteries create voltage through a chemical process. Power plants generate electricity from numerous mechanical methods. Some burn coal or gas to create steam while others use water flowing through a dam on a lake. There are also nuclear-powered generating power plants. All of these power-generating systems turn large turbines that turn the shaft on a generator. All of these sources of electricity convert something called potential energy to kinetic energy. The potential energy is stored in the fuel, whether it is coal, gas, uranium, water in a dam, etc. When we utilize these fuels to generate electricity, they become kinetic energy.

We might say that potential energy is waiting to be used while kinetic energy is being used.

In addition to the voltage source, we need to have wires and other components to build an electric circuit. Remember that copper wires are conductors since they can easily conduct the flow of electrons. We may also use resistors or other forms of loads to form a complete circuit. If we did not include resistors in our circuit, there may be too much current flowing to and from our voltage source and we could damage the voltage source.


  1. Wires and various components connected together form a circuit.
  2. Power plants and fuel cells are some examples of sources that the voltage for any electrical circuit can come from.