The confusion between “voltage” and “electric potential” is common because they are intimately related and often used interchangeably. Both concepts describe the electrical state of a system, but they refer to different aspects of that state. Electric potential describes a condition at a single location in an electric field, whereas voltage describes the difference between two separate locations. Understanding this distinction is the first step toward grasping how electricity truly works.
Electric Potential and the Need for a Reference
Electric potential is a value describing the amount of potential energy stored per unit of positive electric charge at a single point within an electric field. This value exists regardless of whether a charge is present at that location. It is a fundamental property of the space surrounding charged objects, defining the energy landscape for any charge placed there.
Because potential represents stored energy, it is an absolute quantity, but it can only be meaningfully measured relative to an established zero point. This reference point is often called “ground” in practical electronics or, in physics, a point infinitely far away from the electric field. Without defining this baseline, the numerical value of electric potential at a point has little practical meaning.
The need for a reference point is similar to how elevation is measured on Earth. A mountain’s height is an absolute value, but it is always stated relative to sea level, the conventional zero reference. If the electric potential at a point is 10 volts, it means 10 joules of work were required to move one coulomb of positive charge from the zero reference point to that location. This emphasis on a single point and a reference defines electric potential.
Voltage: Measuring the Difference
Voltage is defined exclusively as the electric potential difference (\(\Delta V\)) measured between two distinct points. It represents the driving force that causes electric charge, or current, to flow through a circuit. Voltage is calculated as the work required to move a unit of positive charge from one point to the other.
This measurement is what a voltmeter displays when its probes are placed across two terminals, such as the ends of a battery. The value measured is always relative, quantifying the difference in energy available per unit charge between the two points. The SI unit for both electric potential and voltage is the volt (V), equal to one joule per coulomb.
The energy difference represented by voltage allows electrical work to be done. For example, a light bulb placed between two points with a voltage difference will light up because the charge moving from the higher potential point to the lower potential point releases energy. This movement happens because the electric field pushes the charges, converting the stored potential energy into other forms, like light and heat. Voltage is the practical, measurable quantity that directly relates to current flow and power delivery.
Connecting the Concepts through Real-World Analogies
The terms are frequently used interchangeably because in many practical applications, one point is implicitly set as the zero reference. In a common electrical circuit, the ground wire is assigned a potential of zero volts. When an electrician measures the potential at the “hot” terminal of a wall outlet, the resulting measurement is numerically equal to the voltage between that terminal and the ground reference.
A helpful analogy is a water storage tank. The water level represents the electric potential at that single point, measured as a height above a defined zero level, like the ground. If the tank is 50 meters above the ground, the potential is 50 meters.
Voltage is analogous to the pressure difference created when a pipe runs from the tank to a faucet 20 meters lower. The water’s potential difference, or the pressure available to push the water, is the 20-meter height drop. This pressure difference is the driving force for the water flow, just as voltage drives electrical current flow.
When a battery is labeled “1.5 Volts,” that number represents the voltage between its positive and negative terminals. It tells you the energy available to push one coulomb of charge from the high-potential positive terminal to the low-potential negative terminal. The difference between electric potential and voltage is a matter of scope: one is a value at a point relative to a reference, and the other is the difference between two points.