# Volts, Electric potential energy

When a bunch of electrons congregate in one place, their combined charges build up to a certain level of electric potential energy in that object. For example, when we rub this rubber balloon on the scarf, it causes a bunch of the electrons from the scarf to jump over on the balloon. Now the balloon is negatively charged, because it has a surplus of negatively charged electrons, and the scarf is positively charged, because it has a shortage of electrons.

This imbalance of charge means there’s a difference in the electric potential energy between these two objects. And the difference produces a force which tries to move the excess electrons from the balloon back towards the scarf to equalize the charge.

Volt:

• We use the term voltage to describe the difference in electric potential energy between two points.
• And we’ll use that imbalance of energy to push electrons around when we create electric circuits.
• Voltage is measured using a unit called volts to describe how much more, or less, potential energy there is in one place compared to another.

When describing the voltage of something, it’s critical to know what the point of reference is. What are the volts relative to? The point of reference may not be explicitly defined when working with common voltage sources, but you’re still expected to understand what that voltage means. For example, in a nine volt battery, that single number, nine volts, means there’s a nine volt difference in potential energy between these two terminals.

There’s an insulative barrier inside of the battery that separates the two halves, and the battery works using chemicals inside that act like a pump, to move electrons from the positive side to the negative side.It moves just enough electrons to maintain that nine volt difference between the positive and negative terminals. Looking at another power source, the electrical outlets in UK operate at 220 volts. That voltage is describing the potential difference between these two terminals. By convention, the terminal on the left is called the neutral line, and acts as the point of reference, and the hot terminal on the right is 220 volts relative to the neutral terminal.

In a complex electrical system with lots of components, different points throughout the system will likely be operating at different electric potential energy levels. Therefore, to keep track of the voltages at each of these points throughout a system, it helps to have a single point of reference, the term Ground, or Common,designates that single reference point which is used to describe the voltage at other points throughout an electric circuit. The term Ground comes from the fact that many large electrical systems, like the wiring in your house, are connected to the earth and literally use the ground as that single point of reference.

In practice, the terms Common and Ground tend to get thrown around and used interchangeably, so it’s important to always understand what the voltages in a circuit are actually reference to. To illustrate how multiple voltages can be referenced to a single point, we can use this as an analogy relating electricity to water. In this analogy, you can think of a voltage like a difference in pressure.

In an electrical circuit, we use components called voltage sources, like batteries and power supplies, which maintain a constant potential difference between two points. The connected negative terminal of a nine volt battery on the right, to the positive terminal of the battery on the left. And we’r using that point as the ground reference for the system. Traditionally, black colored wires are used to connect the negative output of a power source, and red wires are used to connect the positive output. Point A is represented by the positive terminal of the right battery, so it’s at positive nine volts relative to the ground. Point B is represented by the negative terminal of the left battery, so the voltage there is negative nine volts relative to the ground. The fact that point A represents positive voltage and point B represents negative voltage is dependent on the battery we chose to serve as our reference for ground.

If we had selected the ground connection to be our point of reference, which has the lowest potential energy respect to positive connection, then both of the other connections would have a positive voltage relative to it. Here in next diagram is that same circuit diagram as before, except we’ve changed which point we’ve decided to call the ground reference to be the negative terminal of the left battery instead of the point in the middle.

Now the point in the middle is at positive nine volts, and point A on the far right is even higher at positive 18 volts, relative to ground.We encounter a wide range of voltages in day to day life, ranging from the relatively small signals that come from an audio jack of an MP3 player, which are usually less than 1 volt, all the way up to the high voltage transmission lines that carry power over long distance which operate at over 115 thousand volts.