The following outline is provided as an overview of and topical guide to electrical polarity (also called electric polarity).

Positive and negative polarity

* In

electrical engineering Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems that use electricity, electronics, and electromagnetism. It emerged as an identifiable occupation in the l ...

, electrical polarity defines the direction in which the

electrical current Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...

would flow once a source is connected; usually used for the

direct current Direct current (DC) is one-directional electric current, flow of electric charge. An electrochemical cell is a prime example of DC power. Direct current may flow through a conductor (material), conductor such as a wire, but can also flow throug ...

sources, where terminals are traditionally labeled with polarity symbols + (positive) and - (negative), with the conventional current chosen to flow from the positive to negative terminal. ** By analogy, when in

electronics Electronics is a scientific and engineering discipline that studies and applies the principles of physics to design, create, and operate devices that manipulate electrons and other Electric charge, electrically charged particles. It is a subfield ...

a signal is observed across two terminals, the measurement of

voltage Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...

between the terminals yields opposing signs for the positive and negative polarity. * In

physics Physics is the scientific study of matter, its Elementary particle, fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge whi ...

and

chemistry Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...

, electric polarity defines the

electric charge Electric charge (symbol ''q'', sometimes ''Q'') is a physical property of matter that causes it to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative''. Like charges repel each other and ...

separation into positive and negative charges within a system or molecule (for example, water molecules have unequal distribution of electrons between the

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

and

hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...

atoms). The quantitative measure of this separation is called an

electric dipole moment The electric dipole moment is a measure of the separation of positive and negative electrical charges within a system: that is, a measure of the system's overall Chemical polarity, polarity. The International System of Units, SI unit for electric ...

. * In

biology Biology is the scientific study of life and living organisms. It is a broad natural science that encompasses a wide range of fields and unifying principles that explain the structure, function, growth, History of life, origin, evolution, and ...

, electrical polarity refers to the sign of the difference in

electric potential Electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as electric potential energy per unit of electric charge. More precisely, electric potential is the amount of work (physic ...

between the parts of a living organism. For example, the inner surface of a

cell membrane The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...

is usually negatively charged with respect to the outer surface (so called

resting potential The relatively static membrane potential of quiescent cells is called the resting membrane potential (or resting voltage), as opposed to the specific dynamic electrochemical phenomena called action potential and graded membrane potential. The re ...

). When this polarity briefly reverses in a

nerve A nerve is an enclosed, cable-like bundle of nerve fibers (called axons). Nerves have historically been considered the basic units of the peripheral nervous system. A nerve provides a common pathway for the Electrochemistry, electrochemical nerv ...

, an opposite

action potential An action potential (also known as a nerve impulse or "spike" when in a neuron) is a series of quick changes in voltage across a cell membrane. An action potential occurs when the membrane potential of a specific Cell (biology), cell rapidly ri ...

is communicated over long distances. The potential is maintained by a sodium-potassium pump. While sodium and potassium ions are both positively charged, their unequal concentration inside and outside of a cell causes the difference in potential. Many electrical devices, from power sources to

loudspeakers A loudspeaker (commonly referred to as a speaker or, more fully, a speaker system) is a combination of one or more speaker drivers, an enclosure, and electrical connections (possibly including a crossover network). The speaker driver is an ...

, operate in parallel. For proper operation, the connectors of these devices are usually "polarized" (either through the use of color-coded cables or plugs where the wires cannot be reversed). File:Water-elpot-transparent-3D-balls.png, Electrical potential of the water molecule (red indicates the negative charge) File:Sodium-potassium pump and diffusion.png, Sodium-potassium pump in a cell membrane (oversimplified) File:Loudspeaker connector female DIN 41529-3350.jpg, Polarized loudspeaker connector and color-coded wire

Anode and cathode

Some

electrical components An electronic component is any basic discrete electronic device or physical entity part of an Electronics, electronic system used to affect electrons or their associated electromagnetic field, fields. Electronic components are mostly industrial ...

are ''non-polar'' and function in the same way regardless of the direction of current through them. For example, properties of a

resistor A resistor is a passive two-terminal electronic component that implements electrical resistance as a circuit element. In electronic circuits, resistors are used to reduce current flow, adjust signal levels, to divide voltages, bias active e ...

are unaffected if the wires on its terminals are swapped. Many other components, however, require a particular direction of current to operate. For terminals of such polarized electrical devices, the anode/cathode terminology is used, with anode being the connection from which the conventional current (positive charges) is flowing inside the component (thus the mnemonic ACID, "Anode Current Into Device"). Anode/cathode terminology is not directly tied to the

of the terminals, generally in a battery anode has negative polarity, while in an electric load − positive, cathode has the opposite polarity: * Inside an

electric battery An electric battery is a source of electric power consisting of one or more electrochemical cells with external connections for powering electrical devices. When a battery is supplying power, its positive Terminal (electronics), terminal is the ...

, positive charges are flowing away from the anode (thus creating negative potential on this

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas). In electrochemical cells, electrodes are essential parts that can consist of a varie ...

, see the illustration) to cathode. * In a

diode A diode is a two-Terminal (electronics), terminal electronic component that conducts electric current primarily in One-way traffic, one direction (asymmetric electrical conductance, conductance). It has low (ideally zero) Electrical resistance ...

, the operating current typically flows from the anode to cathode, an arrow on the diode symbol indicates the direction. There are however, exceptions, like

zener diode A Zener diode is a type of diode designed to exploit the Zener effect to affect electric current to flow against the normal direction from anode to cathode, when the voltage across its terminals exceeds a certain characteristic threshold, the ''Z ...

s, that are connected in a "reverse polarity", with operating current flowing from the cathode to anode. The anode/cathode terminology is also used for a simlar device, a

thyristor A thyristor (, from a combination of Greek language ''θύρα'', meaning "door" or "valve", and ''transistor'' ) is a solid-state semiconductor device which can be thought of as being a highly robust and switchable diode, allowing the passage ...

. * Many

capacitors In electrical engineering, a capacitor is a device that stores electrical energy by accumulating electric charges on two closely spaced surfaces that are insulated from each other. The capacitor was originally known as the condenser, a term st ...

are non-polar, but the electrolytic ones have anodes and cathodes, with anode potential required to be positive with respect to the cathode to avoid damage. * In

electrochemistry Electrochemistry is the branch of physical chemistry concerned with the relationship between Electric potential, electrical potential difference and identifiable chemical change. These reactions involve Electron, electrons moving via an electronic ...

, by convention, anode is always the place for

oxidation Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is ...

, and cathode for reduction. There are two types of cells: galvanic where spontaneous chemical reactions produce electricity (e.g., common electric batteries) and electrolytic where an external electricity source causes chemical reactions (e.g., rechargeable batteries while charging). In a galvanic cell, potential on the cathode is positive with respect to the anode, in electrolytic cells cathode is negative relative to the anode. Diode pinout en fr.svg, Diode

symbol A symbol is a mark, Sign (semiotics), sign, or word that indicates, signifies, or is understood as representing an idea, physical object, object, or wikt:relationship, relationship. Symbols allow people to go beyond what is known or seen by cr ...

and typical polarity marks (bands at the cathode terminal) Zener diode symbol.svg, Zener diode symbol Wiki-Al-Elkos-P1090313-2-Part1.jpg, Polarity marks on an electrolytic capacitor

Transistors

While a

bipolar junction transistor A bipolar junction transistor (BJT) is a type of transistor that uses both electrons and electron holes as charge carriers. In contrast, a unipolar transistor, such as a field-effect transistor (FET), uses only one kind of charge carrier. A ...

(BJT) can be simplistically thought of as two diodes with a shared terminal (anode for the PNP variety), (the transistor polarity is usually expressed based on the prevalence of

charge carriers In solid state physics, a charge carrier is a particle or quasiparticle that is free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and holes. In ...

in the parts of the device: N-type for the regions where the charge flow is primarily due to the electrons (free due to the presence of dono

dopants A dopant (also called a doping agent) is a small amount of a substance added to a material to alter its physical properties, such as electrical or optical properties. The amount of dopant is typically very low compared to the material being do ...

), and P-type for the regions where the flow is mostly due to electron holes (available spaces for additional electrons made possible by mixing in the acceptors). * BJT uses both types of regions (thus the adjective "bipolar") and comes in either PNP or NPN polarity. The polarity is indicated by an arrow depicting the conventional current direction from the emitter to the base. The mnemonics is "Not Points iN" and "Points iN Proudly" for the NPN and PNP transistors respectively. *

Field-effect transistor The field-effect transistor (FET) is a type of transistor that uses an electric field to control the current through a semiconductor. It comes in two types: junction FET (JFET) and metal-oxide-semiconductor FET (MOSFET). FETs have three termi ...

(FET) uses the region of just one type (thus another name, ''unipolar transistor'') and it can be an either

N-channel The field-effect transistor (FET) is a type of transistor that uses an electric field to control the Electric current, current through a semiconductor. It comes in two types: JFET, junction FET (JFET) and MOSFET, metal-oxide-semiconductor FET (M ...

or P-channel device. The wide variety of FET devices causes an elaborate set of polarity marks ( conventional current always flowing "down" in the pictures): :

History

The binary ("polar") nature of electrical phenomena was known for a very long time, its similarities to the magnetic polarity were driving research on electromagnetism, with Ørsted finally succeeding in finding a link between the electricity and magnetism (

Oersted's law In electromagnetism, Ørsted's law, (also spelled Oersted's law), is the physical law stating that an electric current creates a magnetic field. This was discovered on 21 April 1820 by Danish physicist Hans Christian Ørsted (1777–1851),H ...

) in 1820. The use of

plus and minus signs The plus sign () and the minus sign () are Glossary of mathematical symbols, mathematical symbols used to denote sign (mathematics), positive and sign (mathematics), negative functions, respectively. In addition, the symbol represents the oper ...

for the opposing

electrical charge Electricity is the set of physical phenomena associated with the presence and motion of matter possessing an electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by Maxwel ...

s was introduced by

Georg Christoph Lichtenberg Georg Christoph Lichtenberg (; 1 July 1742 – 24 February 1799) was a German physicist, satirist, and Anglophile. He was the first person in Germany to hold a professorship explicitly dedicated to experimental physics. He is remembered for his p ...

in the 18th century. The terms "positive" and "negative" were introduced by

Benjamin Franklin Benjamin Franklin (April 17, 1790) was an American polymath: a writer, scientist, inventor, statesman, diplomat, printer, publisher and Political philosophy, political philosopher.#britannica, Encyclopædia Britannica, Wood, 2021 Among the m ...

in 1747. Franklin compared electricity to fluid, with ”positive” indicating the excess of it, and ”negative” identifying the deficit. Prior to Franklin, nomenclature varied, for example, du Fay called the positive charge “vitreous” (as it can be obtained by rubbing glass), and negative “resinous” (obtained by rubbing

amber Amber is fossilized tree resin. Examples of it have been appreciated for its color and natural beauty since the Neolithic times, and worked as a gemstone since antiquity."Amber" (2004). In Maxine N. Lurie and Marc Mappen (eds.) ''Encyclopedia ...

, “resin”). Berzelius, in his early 19th century work on

, used the term "electrical polarity" to explain the

chemical reactions A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. When chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an energy change as new products ...

. Per Berzelius, while all atoms possessed both positive and negative polarities (

electrochemical dualism Electrochemical dualism is an obsolete scientific theory in chemistry relevant between around 1800 and around 1830 and pioneered by Jöns Jacob Berzelius.''Jöns Jacob Berzelius'', Richard A. Pizzi, Today's Chemist At Work, 2004, page 58 The theory ...

, long obsolete), the balance depended on an element (with, for example, oxygen being negative and

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

positive), and the reactions were caused by the electrical attraction between the atoms. The terms ''anode'' and ''cathode'', roughly meaning, respectively, "way up" and "way down" in Greek, were introduced by

Faraday Michael Faraday (; 22 September 1791 – 25 August 1867) was an English chemist and physicist who contributed to the study of electrochemistry and electromagnetism. His main discoveries include the principles underlying electromagnetic inducti ...

. Knowing well the

Earth's magnetic field Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from structure of Earth, Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from ...

stretching North to South and assuming that it was generated by a conventional current, the direction of this current, per

Ampère's circuital law In classical electromagnetism, Ampère's circuital law, often simply called Ampère's law, and sometimes Oersted's law, relates the circulation of a magnetic field around a closed loop to the electric current passing through the loop. James ...

, should be East to West. Sun in the East goes "up" and in the West "down", hence the terminology.

References

Sources