Electric current direction
The electrical current direction is the direction of the electric current on.
definition
Electric current is flowing electric charge . In physics and technology, the direction of the current or direction of the electrical current is defined as the direction in which positive electrical charge moves. Outside of current or voltage sources , it (and with it the current) therefore flows - following the direction of the field lines of the electric field - from the positive pole to the negative pole, inside the sources on the other hand to close the circuit , then on from the negative to the positive pole, etc. This applies regardless of the type of charge carrier as a logical consequence of the continuity equation .
In a diagram for an electrical circuit , the direction of the electrical current is indicated by a counting arrow , the direction of which usually corresponds to the direction of the electrical current. If it turns out that the electrical current direction is opposite to the counting arrow, the current intensity is given a negative value in relation to the arrow direction.
Charge current versus charge carrier current
The direction of the electrical current (= "technical current direction") is indicated with red arrows . Green arrows mark the direction of flow of the negatively charged charge carriers, in the metal wire these are electrons.
Colloquially, the competing terms of the so-called “technical” and “physical” direction of the current appear. In fact, however, the electrical current direction is identical to the “technical” current direction and is defined exactly the same in physics and electrical engineering.
The term " technical direction of current " is primarily due to historical reasons; it is based on a stream of charges which - following the direction of the electric field line - move from the positive to the negative voltage pole. The fact that it is the electrons in metallic conductors that cause the current to flow as charge carriers and that they flow exactly the other way around from the negative to the positive pole was not yet known at the time when the term was created. The definition of the direction of electrical current was retained as a uniform convention even after the discovery of electrons almost a century later. The determination of the sign of the current direction is directly linked to the determination of the sign of the charge; the only type of charge originally assumed was positive. The charge of the electrons moving in the opposite direction was then declared negative, while maintaining the law of electrostatic force .
In contrast, the term of " physical flow direction is not" the flow of electrical charge, but a mass , volume , particle , or quantum mechanical (stay) probability flow of electrical charge carriers . It thus characterizes the movement of the electrical charge carriers regardless of their respective charge. In some cases, it is left open which load carriers are involved; often electrons in metals are meant that by convention have a negative charge. Then the electron flow (“physical current direction”), as shown in the figure, is opposite to the (positive) charge flow (“technical current direction”).
Since there are a number of other charge carriers in addition to electrons that can contribute positively or negatively charged to the charge transport and thus to the current - in semiconductors , during electrolysis or in gas discharges - the term "physical current direction" is not only misleading, but occasionally also ambiguous. It is therefore better to speak of the direction of movement of the respective charge carriers from the outset , for example the “electron flow direction” or the direction of movement of the negative or positive ions or defect electrons .
The actual non-existent conflict between technology and physics only arises if a careful distinction is not made between charge and charge carriers.
The current direction in the external circuit from the positive pole to the negative pole of the source is referred to as “ conventional current direction ”. It corresponds to the technical direction of the current.
Representation of the direction of current flow perpendicular to the plane of the drawing
In order to represent directions transverse to the plane of the drawing, the symbols ⊙ (out of the plane to the viewer) and ⊗ (from the viewer into the plane) are used for the direction of the electric current . An arrow can be imagined as a donkey bridge to keep these symbols: When the arrow flies towards the observer, only the point of the tip can be seen. If the arrow flies away from the observer, feathers can be seen at the end of the arrow as a cross.
Alternating current
An electric current whose direction changes in regular repetition is called alternating current . A counting arrow for the direction of the electric current makes sense when considering instantaneous values. Furthermore, the counter arrow is used in circuit diagrams in such a way that it shows the direction of the mean energy flow . This is independent of the changing direction of the electric current. The direction of the arrow thus indicates the sign of the active power carried over the line with the usual sign regulation .
Web links
Individual evidence
- ↑ DIN EN 60375, agreements for electrical circuits and magnetic circuits , chap. 4.1, 2004
- ↑ IEC 60050, see DKE German Commission for Electrical, Electronic and Information Technologies in DIN and VDE: International Electrotechnical Dictionary entry 131-11-29
- ↑ Ludwig Bergmann, Clemens Schaefer: Textbook of Experimental Physics, Volume 2: Electricity . Walter de Gruyter, 1966, p. 124
- ↑ Wilfried Plaßmann, Detlef Schulz: Handbook of electrical engineering: Basics and applications for electrical engineers . Vieweg + Teubner, 2009, p. 256
- ^ Karl Küpfmüller: Theoretical electrical engineering and electronics. 14th edition, Springer Verlag 1993, ISBN 3-540-56500-0 .
- ↑ Marlene Marinescu, Nicolae Marinescu: Electrical engineering for study and practice: direct, alternating and three-phase currents, switching and non-sinusoidal processes . Springer Vieweg, 2016, p. 2
- ↑ Horst Clausert, Gunther Wiesemann, Volker Hinrichsen, Jürgen Stenzel: Basic areas of electrical engineering 1: DC networks, operational amplifier circuits, electrical and magnetic fields. Oldenbourg, 11th edition 2011, p. 7
- ^ Wolfgang Courtin: Electrical energy technology: Introduction for all courses. Vieweg, 1999, p. 43 f
- ↑ DIN 40110-1: 1994 alternating current quantities , chap. 3.1.