What Is Voltage? (Definition)

Voltage is the electromotive force or the electric potential energy difference between two points (often within the context of an electrical circuit) per unit of charge, expressed in volts (V). Voltage, along with current and resistance, describes the behavior of electrons. The relationships are observed through the application of Ohms law and Kirchhoff's circuit laws.

Voltage: An Example of the Concept

The concepts of voltage, charge, current, and resistance can be explained with a bucket of water and a hose attached to the bottom. The water represents charge (and the movement of electrons). The flow of water through the hose represents current. The width of the hose represents resistance; a skinny hose would have less flow than a wider hose. The amount of pressure created at the end of the hose by the water represents voltage.

If you were to pour one gallon of water into the bucket while covering the end of the hose with your thumb, the pressure you feel against the thumb is similar to how voltage works. The potential energy difference between the two points — the top of the water line and the end of the hose — is just that one gallon of water. Now let's say that you found a bucket large enough to be filled with 450 gallons of water (roughly enough to fill a six-person hot tub). Imagine the kind of pressure your thumb might feel while attempting to hold that quantity of water back.

Putting It All Together

Voltage (the cause) is what makes the current (the effect) happen; without any voltage push to force it, there would be no flow of electrons. The amount of electron flow created by voltage is important with respect to the work that needs to be done. A few 1.5 V AA batteries are all you need to power a small remote-controlled toy. But you wouldn't expect those same batteries to be able to run a major appliance requiring 120 V, such as a refrigerator or clothes dryer. Consider the voltage specifications with electronics, particularly when comparing protection ratings on surge protectors.

The United States electrical grid, for example, operates at 120 V (at 60 Hz), which means you can use a 120 V stereo receiver with a pair of speakers. But in order for that same stereo receiver to work safely in Australia, which operates at 240 V (at 50 Hz), you need a power converter and plug adapter.