Editing Electric charge (section)

== Overview ==
[[File:Electric field point lines equipotentials.svg|thumb|right|250px|Diagram showing field lines and [[equipotential]]s around an [[electron]], a negatively charged particle. In an electrically neutral [[atom]], the number of electrons is equal to the number of protons (which are positively charged), resulting in a net zero overall charge]]

Charge is the fundamental property of matter that exhibits [[electrostatic]] attraction or repulsion in the presence of other matter with charge. Electric charge is a characteristic property of many [[charged particle|subatomic particles]]. The charges of free-standing particles are integer multiples of the elementary charge ''e''; we say that electric charge is ''[[charge quantization|quantized]]''. [[Michael Faraday]], in his [[electrolysis]] experiments, was the first to note the discrete nature of electric charge. [[Robert Millikan]]'s [[oil drop experiment]] demonstrated this fact directly, and measured the elementary charge. It has been discovered that one type of particle, [[quark]]s, have fractional charges of either −{{sfrac|1|3}} or +{{sfrac|2|3}}, but it is believed they always occur in multiples of integral charge; free-standing quarks have never been observed.

[[Convention (norm)|By convention]], the charge of an [[electron]] is negative, ''−e'', while that of a [[proton]] is positive, ''+e''. Charged particles whose charges have the same sign repel one another, and particles whose charges have different signs attract. [[Coulomb's law]] quantifies the electrostatic [[force]] between two particles by asserting that the force is proportional to the product of their charges, and [[inverse-square law|inversely proportional to the square]] of the distance between them. The charge of an [[antiparticle]] equals that of the corresponding particle, but with opposite sign.

The electric charge of a [[macroscopic]] object is the sum of the electric charges of the particles that it is made up of. This charge is often small, because matter is made of [[atom]]s, and atoms typically have equal numbers of [[proton]]s and [[electron]]s, in which case their charges cancel out, yielding a net charge of zero, thus making the atom neutral.

An ''[[ion]]'' is an atom (or group of atoms) that has lost one or more electrons, giving it a net positive charge (cation), or that has gained one or more electrons, giving it a net negative charge (anion). ''Monatomic ions'' are formed from single atoms, while ''polyatomic ions'' are formed from two or more atoms that have been bonded together, in each case yielding an ion with a positive or negative net charge.
{{multiple image
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| image1    = VFPt plus thumb.svg
| alt1      = [[Electric field]] induced by a positive electric charge
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| image2    = VFPt minus thumb.svg
| alt2      = Electric field induced by a negative electric charge
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| footer    = Electric field induced by a positive electric charge (left) and a field induced by a negative electric charge (right).
}}

During the formation of macroscopic objects, constituent atoms and ions usually combine to form structures composed of neutral ''ionic compounds'' electrically bound to neutral atoms. Thus macroscopic objects tend toward being neutral overall, but macroscopic objects are rarely perfectly net neutral.

Sometimes macroscopic objects contain ions distributed throughout the material, rigidly bound in place, giving an overall net positive or negative charge to the object. Also, macroscopic objects made of conductive elements can more or less easily (depending on the element) take on or give off electrons, and then maintain a net negative or positive charge indefinitely. When the net electric charge of an object is non-zero and motionless, the phenomenon is known as [[static electricity]]. This can easily be produced by rubbing two dissimilar materials together, such as rubbing [[amber]] with [[fur]] or [[glass]] with [[silk]]. In this way, non-conductive materials can be charged to a significant degree, either positively or negatively. Charge taken from one material is moved to the other material, leaving an opposite charge of the same magnitude behind. The law of ''[[conservation of charge]]'' always applies, giving the object from which a negative charge is taken a positive charge of the same magnitude, and vice versa.

Even when an object's net charge is zero, the charge can be distributed non-uniformly in the object (e.g., due to an external [[electromagnetic field]], or bound polar molecules). In such cases, the object is said to be [[polarization density|polarized]]. The charge due to polarization is known as [[bound charge]], while the charge on an object produced by electrons gained or lost from outside the object is called ''free charge''. The motion of electrons in conductive [[metal]]s in a specific direction is known as [[electric current]].