Voltage is a somewhat familiar term, but let’s discuss what it actually is. Like mass has a gravitational potential energy, charged particles have associated with them an electric potential energy. If multiple charged particles create electric fields that affect one another, these particles will then gain a potential to move because of the electric forces that influence them.
Think of it this way: if a positively charged particle comes into contact with a negative electric field, the electric field will create a “hill”, where the downhill direction would be in the direction of the electric field. This positive charge would naturally want to “roll” down the hill towards the field, thus it has a positive potential energy at the top of the hill, and no potential energy when it reaches the bottom of the “hill”. In the case below, we have a proton between two oppositely charged plates and therefore the electric field is directed toward the negative plate. The field does work on the particle, or gives potential energy to the particle, to move it towards the negatively charged plate. To move the particle towards the positive plate would mean it would be going “uphill”, or in the opposite direction of the electric field. (Note: the “hill” is an analogy that really is relating electric fields with gravitational fields, something that is more familiar to us).
Source: sdsu-physics.org. 29 Feb. 2012.
We can define a voltage potential as the potential energy per unit charge, with units of Volts (V). In the figure above we have a capacitor (see “Circuits (Resistors and Capacitors)”) that stores charge, and because each plate has an opposite charge an electric field is created between them, and consequently a voltage. This voltage is what causes the proton to naturally move toward the negatively charged plate. In “Electric Current” we will discuss how this voltage causes electrons to move through a wire.