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## PowerPedia:Electric charge

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Electric charge is determines their There was an error working with the wiki: Codes. Electrically charged matter is influenced by, and produces, Electromagnetic fields. The interaction between a moving charge and the electromagnetic field is the source of the There was an error working with the wiki: Code. In mainstreasm physics, it is the conserved property of some There was an error working with the wiki: Code and is one of the four There was an error working with the wiki: Codes.

#### Characteristics

There are only two kinds of electrical charge. One is called positive and the other is called negative. Two objects that have been charged alike repel each other. Two objects that have been oppositely charged attract each other.

##### Subatomic

Electric charge is a characteristic of some subatomic particles, and is quantized when expressed as a multiple of the so-called elementary charge e. Electrons by convention have a charge of ?1, while protons have the opposite charge of +1. Quarks have a fractional charge of ?1/3 or +2/3. The antiparticle equivalents of these have the opposite charge. There are other charged particles. In general, same-sign charged particles repel one another, while different-sign charged particles attract. This is expressed quantitatively in Coulomb's law, which states the magnitude of the repelling force is proportional to the product of the two charges and decays as the square of the distance. Formally, a measure of charge should be a multiple of the elementary charge e (charge is quantized), but since it is an average, macroscopic quantity, many orders of magnitude larger than a single elementary charge, it can effectively take on any real value. Furthermore, in some contexts it is meaningful to speak of fractions of a charge e.g. in the charging of a capacitor.

The electric charge of a macroscopic object is the sum of the electric charges of its constituent particles. Often, the net electric charge is zero, since naturally the number of electrons in every atom is equal to the number of the protons, so their charges cancel out. Situations in which the net charge is non-zero are often referred to as static electricity.

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The electric charge can be distributed non-uniformly (e.g., due to an external electric field), and then the material is said to be polarized, and the charge related to the polarization is known as bound charge (while the excess charge brought from outside is called free charge). An ordered motion of charged particles in a particular direction (typically these are the electrons) is known as electric current.

The SI unit of electric charge is the coulomb, which represents approximately 6.24 × 1018 elementary charges (the charge on a single electron or proton). The coulomb is defined as the quantity of charge that has passed through the cross-section of a conductor carrying one ampere within one second. The symbol Q is often used to denote a quantity of electric charge.

##### Conservation of charge

The total electric charge of an There was an error working with the wiki: Code I:

:- \frac{\partial}{\partial t} \int_V \rho\, dV = \int_S {J} \cdot {dS} = I

The charge is a relativistic invariant. This means that any particle that has charge q, no matter how fast it goes, always has charge q. This property has been experimentally verified by showing that the charge of one helium nucleus (two protons and two neutrons bound together in a nucleus and moving around at high speeds) is the same as two deuterium nuclei (one proton and one neutron bound together, but moving much more slowly than they would if they were in a helium nucleus).

#### History

As reported by the Ancient Greek philosopher There was an error working with the wiki: Code, charge (or electricity) could be accumulated by rubbing There was an error working with the wiki: Code on various substances, such as There was an error working with the wiki: Code. The Greeks noted that the charged amber buttons could attract light objects such as There was an error working with the wiki: Code. They also noted that if they rubbed the There was an error working with the wiki: Code for long enough, they could even get a spark to jump. This property derives from the There was an error working with the wiki: Code.

In There was an error working with the wiki: Code, who in There was an error working with the wiki: Codes and There was an error working with the wiki: Codes and There was an error working with the wiki: Code, who proposed in There was an error working with the wiki: Code http://www.sparkmuseum.com/BOOK_DUFAY.HTM that electricity came in two varieties which cancelled each other, and expressed this in terms of a two-fluid theory. When glass was rubbed with silk, DuFay said that the glass was charged with vitreous electricity, and when amber was rubbed with fur, the amber was said to be charged with resinous electricity.

One of the foremost experts on electricity in the There was an error working with the wiki: Code arrived at the same explanation at about the same time.

We now know that the Franklin/Watson model was close, but too simple. Matter is actually composed of several kinds of electrically charged particles, the most common being the positively charged There was an error working with the wiki: Code There was an error working with the wiki: Code), two or more species of electric charges flow in opposite directions. The flow direction for conventional current is also backwards compared to the actual electron drift taking place during electric currents in metals, the typical conductor of electricity, which is a source of confusion for beginners in electronics.

The discrete nature of electric charge was demonstrated by Robert Millikan in his oil-drop experiment. The Electric charge was measured with an electrometer.

#### References, sources, and further reading

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Old Man, "Electric Charge On a Planet". sci.physics.relativity, sci.physics, Aug 1 2003.

Charles François de Cisternay DuFay Two Kinds of Electrical Fluid: Vitreous and Resinous - 1733, sparkmuseum.com.

Larry Mead, Does electrical charge distort spacetime?. sci.physics, Dec 3 1998.

Ron Kurtus, Electrical Charges, school-for-champions.com, 16 August 2005

Electric charge and Coulomb's law. physics.bu.edu, 7-6-99

How fast does a charge decay?

Science Aid: Electrostatic charge Easy to understand page on electrostatic charge.

There was an error working with the wiki: Code, Wikipedia: The Free Encyclopedia. Wikimedia Foundation.

Alberto Mesquita Filho, Electron and electric charge. alt.sci.physics.new-theories, Sep 10 2000.