Electrical voltage - Part 1

Voltage is the amount of specific potential energy available between two points in an electric circuit.

Potential energy is energy that is potentially available to do work. Looking at this from a classical physics perspective, potential energy is what we accumulate when we lift a weight above ground level, or when we compress a spring:

In either case, potential energy is calculated by the work done in exerting a force over a parallel distance. In the case of the weight, potential energy (Ep) is the simple product of weight (gravity g acting on the mass m) and height (h):

Ep = mgh

Energy calculations for springs are more complex than for weights. The force exerted by the spring against the compressing motion increases with compression (F = kx, where k is the elastic constant of the spring).

 It does not remain steady as the force of weight does for the lifted mass. Therefore, the potential energy equation is nonlinear:

Ep= .5 K * x^2

Releasing the potential energy stored in these mechanical systems is as simple as dropping the mass, or letting go of the spring. The potential energy will return to the original condition (zero) when the objects are at rest in their original positions. If either the mass or the spring were attached to a machine to harness the return-motion, that stored potential energy could be used to do useful tasks.

Potential energy may be similarly defined and quantified for any situation where we exert a force over a parallel distance, regardless of where that force or the motivating distance comes from. For instance, the static cling you experience when you pull a wool sock out of a clothes dryer is an example of a force. By pulling that sock away from another article of clothing against the force of “static cling,” you are doing work, and storing potential energy in the tension between that sock and the rest of the clothing. In a similar manner, that stored energy could be released to do useful tasks if we placed the sock in some kind of machine harnessing the sock’s motion as it returns to its original position on the pile of laundry, pulled by the force of static electrical attraction.

If we make use of non-mechanical means to move electric charge from one location to another, the result is no different. Moving attracting charges apart from one another means doing work (a force exerted over a parallel distance) and storing potential energy in that physical tension. When we use chemical reactions to move electrons from one metal plate to another in a solution, or when we spin a generator and electro-magnetically motivate electrons to seek other locations, we impart potential energy to those electrons. We could express this potential energy in the same unit as we do for mechanical systems (the Joule). However, it is actually more useful to express the potential energy in an electric system in terms of how many joules are available per a specific quantity of electric charge (a certain number of electrons). This measure of specific potential energy is simply called electric potential or voltage, and we measure it in units of Volts, in honor of the Italian physicist Alessandro Volta, inventor of the first electrochemical battery.

1 Volt = 1 Joule of potential energy / 1 Coulomb of electric charge

In other words, if we forced 1 Coulomb’s worth of electrons (6.24 × 1018 of them, to be exact) away from a positively-charged place, and did one Joule’s worth of work in the process, we would have generated one Volt of electric potential.