By Jeffrey Ober | April 21, 2023 | 1:06 p.m. EST
Potential difference, commonly referred to as voltage, is the driving force behind electric current. A higher voltage pushes more current through a circuit, just as a steeper hill encourages a faster roll. In a closed loop, voltage is the energy per unit charge that moves a charged particle from one point to another. Expressed in joules per coulomb, its SI unit is the volt (V).
Mathematically, voltage is defined as:
V = E / Q = J / C
Here, E is the electric energy in joules (J), and Q is the electric charge in coulombs (C). The voltage determines how strongly a positive charge (or a negative charge in the opposite direction) is pushed over a given distance.
Volt is named after Alessandro Volta, a pioneer in electricity and magnetism.
Voltage can also be viewed as force (newtons) acting over a distance (meters). In this sense, it represents the work done to move charge between two points.
In practical circuits, voltage is typically measured across a battery, resistor, or any other element. The battery’s potential difference between its negative and positive terminals sets the current flow. The resistor, in turn, limits this flow, maintaining equilibrium.
These three fundamental quantities—current (I), voltage (V), and resistance (R)—are tied together by Ohm’s Law:
I = V / R
Current quantifies the amount of charge passing a point per second, measured in amperes (A). One ampere equals one coulomb per second. Though the definition is circular—an ampere is coulombs per second—this representation clarifies that current is a real, measurable flow of charge.
Conventional current assumes positive charges move from the battery’s positive terminal to the negative. In reality, electrons—negatively charged particles—travel in the opposite direction, but both descriptions reflect the same energy transfer.
Electricians, engineers, and scientists typically use a multimeter to measure voltage, current, and resistance in a single device.
Even stationary charges generate an electric field described by Coulomb’s law:
E = kQ / r²
where Q is the charge in coulombs, k is Coulomb’s constant, and r is the distance from the charge in meters. This field’s strength allows us to compute the electric potential energy at a given point.
The same relationship leads to the electric force between charges: F = Eq. This branch of physics is known as electrostatics.
Using a test charge, we can derive the electric potential due to a point charge:
V = kQ / r
Unlike the electric field, which diminishes with the square of distance, potential decreases linearly with distance.
Voltage is the cornerstone of modern electronics—powering outlets, car batteries, smartphones, and lighting. In more complex circuits, components such as capacitors (two plates separated by a dielectric) and inductors shape the flow of current to achieve desired effects.
Moreover, moving charges generate magnetic fields, linking electric potential difference to the broader electromagnetic spectrum. This interplay underpins technologies like radio, satellite communication, and wireless power transfer.
