current

a flow of electricity through a conductor

"the current was measured in amperes" a steady flow of a fluid (usually from natural causes)

"the raft floated downstream on the current"

"he felt a stream of air"

"the hose ejected a stream of water" dominant course (suggestive of running water) of successive events or ideas

"two streams of development run through American history"

"stream of consciousness"

"the flow of thought"

"the current of history" occurring in or belonging to the present time

"current events"

"the current topic"

"current negotiations"

"current psychoanalytic theories"

"the ship's current position"

In electricity, current refers to electric current, which is the flow of electric charge. Lightning is an example of an electric current, as is the solar wind, the source of the polar aurora. Probably the most familiar form of electric current is the flow of electrical conductionconduction electronelectrons in a metallic wire. This is how utility companies deliver electricity. In electronics, electric current is most often the flow of electrons through Conductor (material)conductors and devices such as resistors, but it is also the flow of ionions inside a Battery (electricity)battery or the flow of Electron holeholes within a semiconductor.

Relation between current and charge - The symbol typically used for the amount of current (the amount of charge ''Q'' flowing per unit of time ''t'') is ''I'', from the German word ''Intensität'', which means 'intensity'.:$I\; =$Formally this is written as:$i(t)\; =$ or inversely as $q(t)\; =\; \backslash int\_\; ^\; i(x)\backslash ,\; dx$

Conventional current - Conventional current was defined early in the history of electrical science as a flow of positive charge. In solid metals, like wires, the positive charges are immobile, and only the negatively charged electrons flow in the direction opposite conventional current, but this is not the case in most non-metallic conductors. In other materials, charged particles flow in both directions at the same time. Electric currents in electrolytes are flows of electrically charged atoms (ions), which exist in both positive and negative varieties. For example, an electrochemistryelectrochemical cell may be constructed with salt water (a solution of sodium chloride) on one side of a membrane and pure water on the other. The membrane lets the positive sodium ions pass, but not the negative chlorine ions, so a net current results. Electric currents in Plasma physicsplasma are flows of electrons as well as positive and negative ions. In ice and in certain solid electrolytes, flowing protons constitute the electric current. To simplify this situation, the original definition of conventional current still stands. There are also instances where the electrons are the charge that is physically moving, but where it makes more sense to think of the current as the movement of positive "electron holeholes" (the spots that should have an electron to make the conductor neutral). This is the case in a p-type semiconductor.The SI unit of electrical current is the ampere. Electric current is therefore sometimes informally referred to as ''amperage'' or ''ampage'', by analogy with the term ''voltage''. Though this is a valid term, some engineers frown on it.

The speed of an electric current - The charged particles whose movement causes an electric current do not always move in straight lines. In metals, for example, they follow an erratic path, bouncing from atom to atom, but generally drifting in the direction of the electric field. The speed at which they drift can be calculated from the !equation::

Current density - Current density is the current per unit (cross-sectional) area.Mathematically, current is defined as the net flux through an area. Thus::$I\; =\; j\; \backslash cdot\; A$where, in the MKS or SI system of measurement, I'' is the current, measured in amperesj'' is the "current density" measured in amperes per square metreA'' is the area through which the current is flowing, measured in square metresThe current density is defined as::$j=\backslash int\_i\; n\_i\; \backslash cdot\; x\_i\; \backslash cdot\; \backslash mathbf$where n'' is the particle density (number of particles per unit volume)x'' is the mass, charge, or any other characteristic whose flow one would like to measure.u'' is the average velocity of the particles in each volumeCurrent density is an important consideration in the design of electrical and electronic systems. Most electrical conductors have a finite, positive resistance, making them dissipate power in the form of heat. The current density must be kept sufficiently low to prevent the conductor from melting or burning up, or the insulating material failing. In superconductivitysuperconductors, excessive current density may generate a strong enough magnetic field to cause spontaneous loss of the superconductive property.

Electromagnetism - Every electric current produces a magnetic field. The magnetic field can be visualized as a pattern of circular field lines surrounding the wire.Electric current can be directly measured with a galvanometer, but this method involves breaking the circuit, which is sometimes inconvenient. Current can also be measured without breaking the circuit by detecting the magnetic field it creates. Devices used for this include Hall effect sensors, current clamps and Rogowski coils.

Ohm's law - Ohm's law predicts the current in an (ideal) resistor (or other ohmic device) to be the quotient of applied voltage over electrical resistance::$I\; =\; \backslash frac$where I'' is the current, measured in amperesV'' is the potential difference measured in voltsR'' is the electrical resistanceresistance measured in ohms

Electrical safety - The danger of an electric shock depends on the current (in milliamperes), duration and the current's path in the body:

1 mA causes a tingle

5 mA causes a slight shock

50 to 150 mA may result in death, e.g. through rhabdomyolysis (muscle breakdown) and resultant acute renal failure

1-4 A causes ventricular fibrillation

10 A causes cardiac arrest (only at this current will a typical home fuse break the circuit)Currents through the heart and the nervous system are the most dangerous. As most dangerous sources are voltage sources, the current present depends on the resistance of the body between the points of contact and any current limiting built into the source. The comparison between the dangers of alternating current and direct current has been a subject of debate ever since the War of Currents in the 1880s. DC tends to cause continuous muscular contractions that make the victim hold on to a live conductor, thereby increasing the risk of deep tissue burns. On the other hand, mains-frequency AC tends to interfere more with the heart's electrical pacemaker, leading to an increased risk of fibrillation. AC at higher frequencies holds a different mixture of hazards, such as RF burns and the possibility of tissue damage with no immediate sensation of pain.

See also -

Alternating current

Direct current

electrical conduction for more information on the physical mechanism of current flow in materials

SI electromagnetism units

External links -

unitconversion.org - Online Current Converter - convert between various units of current, such as ''ampere'', ''biot'', ''abampere'', ''statampere'', and so on

unitconversion.org - Interactive Current Conversion Table - convert selected unit to all other units of current

amasci.com - Which direction does electricity ''really'' !flow?Category:Electromagnetism Category:Magnetismar:تيار? !كهربائيca:Correntcs:Ele ktrický? proudda:Elektrisk strømde:Elektrischer !Stromet:Elektrivooles:Corrient e? eléctricafr:Courant électriquehe:זרם חשמליko:전류id:Arus listrikit:Corrente elettricanl:Elektrische stroomja:電流pl:Natężenie prądu elektrycznegopt:Corrente elétricaru:Сила токаsk:Elektrický prúdsl:Električni !tokth:กระแสไฟฟ ้าfi:Sähkövirtazh:电流

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