Electric charge

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Electric charge is a basic property of electrons, protons and other subatomic particles. Electrons are negatively charged while protons are positively charged. Things that are negatively charged and things that are positively charged pull on (attract) each other. This makes electrons and protons stick together to form atoms. Things that have the same charge push each other away (they repel each other). This is called the Law of Charges. It was discovered by Charles Augustin de Coulomb. The law that describes how strongly charges pull and push on each other is called Coulomb's Law.

Things that have equal numbers of electrons and protons are neutral. Things that have more electrons than protons are negatively charged, while things with fewer electrons than protons are positively charged. Things with the same charge repel each other. Things that have different charges attract each other. If possible, the one with too many electrons will give enough electrons to match the number of protons in the one that has too many protons for its load of electrons. If there are just enough electrons to match the extra protons, then the two things will not attract each other anymore. When electrons move from a place where there are too many to a place where there are too few, that is called an electrical current.

When a person shuffles his feet on a carpet and then touches a brass doorknob, he or she may get an electrical shock. If there are enough extra electrons then the force with which those electrons push each other away may be enough to make some of the electrons jump across a gap between the person and the doorknob. The length of the spark is a measure of voltage or "electrical pressure." The number of electrons that move from one place to another per unit of time measured as amperage or "rate of electron flow."

If a person gets a positive or negative charge, it may make the person's hairs stand up because the charges in each hair push it away from the others.

Electric charge felt when one gets a shock from a doorknob or other object usually is between 25 thousand and 30 thousand volts. However the amperage involved is incredibly low so the flow of electrons through the person's body can not cause physical harm. On the other hand, when clouds gain electrical charges they have even higher voltages and the amperage (the number of electrons that will flow in the lightning strike) can be very high. That means that electrons can jump from a cloud to the earth (or from the earth to a cloud), and if those electrons go through a person then that person will be burned and may die.

Historical experiment[change | change source]

Electric charge is the fundamental properties of sub atomic particles, that provides an electric field between them. Let a piece of glass and a piece of resin–neither of which exhibits any electrical properties–be rubbed together and left with the rubbed surfaces in contact. They will still exhibit no electrical properties. Let them be separated. They will now attract each other.

If a second piece of glass is rubbed with a second piece of resin, and if the pieces be then separated and suspended in the neighborhood of the former pieces of glass and resin, it may be observed:

1) that the two pieces of glass repel each other.

2) that each piece of glass attracts each piece of resin.

3) that the two pieces of resin repel each other.

These phenomena of attraction and repulsion are called Electrical phenomena and the bodies which exhibit them are said to be 'electrified', or to be 'charged with electricity'.

Besides being electrified by friction, bodies may be electrified in many other ways.

When two substances are rubbed together and an electrical charge is produced, one of them will give electrons to the other. The reason is that the atoms in the two substances have unequal power to attract electrons. So the one that is more able to attract electrons will rob electrons from the one that has a lower attractive force. In one pair of substances rubbed together, the one made of glass may either give or take electrons. What happens depends on the nature of the other member of that pair.

If a body electrified in any manner whatever behaves as the glass does when rubbed with resin, that is, if it repels the glass and attract the resin, the body is said to be 'vitreously' electrified, and if it attracts the glass and repels the resin it is said to be 'resinously' electrified. All electrified bodies are found to be either vitreously or resinously electrified.[source?]

It is the established practice of men of science to call the vitreous electrification positive, and the resinous electrification negative. The exactly opposite properties of the two kinds of electrification justify us in indicating them by opposite signs but the application of the positive sign to one rather than to the other kind must considered as a matter of arbitrary (random choice) convention (agreement), just as it is a matter of convention in mathematical diagrams to reckon positive distance towards the right hand.

No force, either of attraction or of repulsion (the opposite of attraction), can be observed between an electrified body and a body not electrified.

The above experiment is described by James Clerk Maxwell in his magnum opus (great work) A Treatise on Electricity and Magnetism.