Voltage

Lore & Background

Voltage between points can be caused by the build-up of electric charge, such as in a capacitor, and from an electromotive force, such as electromagnetic induction in a generator. On a macroscopic scale, a potential difference can be caused by electrochemical processes like cells and batteries, the pressure-induced piezoelectric effect, the photovoltaic effect, and the thermoelectric effect. Since voltage is the difference in electric potential, it is a physical scalar quantity.

A voltmeter can be used to measure the voltage between two points in a system. Often a common reference potential such as the ground of the system is used as one of the points. In this case, voltage is often mentioned at a point without completely mentioning the other measurement point. A voltage can be associated with either a source of energy or the loss, dissipation, or storage of energy.

Historically, voltage has been referred to using terms like 'tension' and 'pressure'. Even today, the term 'tension' is still used, for example within the phrase 'high tension' (HT) which is commonly used in the contexts of automotive electronics and systems using thermionic valves (vacuum tubes).

Reader's Guide

Voltage is a fundamental concept in physics and electrical engineering, representing the difference in electric potential between two points. Its definition as work per unit charge (joule per coulomb) underpins the SI unit of the volt. The causes of voltage are diverse, ranging from static charge buildup and electromagnetic induction to electrochemical, piezoelectric, photovoltaic, and thermoelectric effects, making it central to understanding and designing electrical systems from batteries to generators.

Voltage is measured with a voltmeter, often using a common ground reference. The concept is defined so that conventional current flows from higher to lower voltage, and negatively charged objects are pulled toward higher voltages. In electrostatics, voltage is path-independent, but in electrodynamics with time-varying magnetic fields, the line integral of the electric field may be used instead, leading to some authors distinguishing 'voltage' from electric potential differences.

The historical terms 'tension' and 'pressure' persist in contexts like 'high tension' in automotive and vacuum tube systems. The SI definition of the volt has evolved, from using power and current to the Josephson effect and, since 2019, defined physical constants. Voltage remains a key quantity for energy transfer, storage, and dissipation in all electrical circuits.

Did You Know?

• Voltage is also known as electric pressure or electric tension.
• The SI unit of voltage is the volt, defined as 1 joule per coulomb.
• A voltmeter is used to measure voltage between two points, often using a common ground reference.
• Voltage can be caused by electrochemical processes, the piezoelectric effect, the photovoltaic effect, and the thermoelectric effect.