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Electric Charge

Charge is a fundamental property of matter. A charged particle will repel or attract another charged particle. Charge must always conserve, e.g. it cannot disappear or me created out of nothing.

All matter is made of charged particles (protons + and electrons -) but it looks neutral (without electrical charge) because the positive and negative charges mix together and the average result is no charge, so that we don't notice a lot of electrical effects in our daily lives (unless we use electric devices, obviously).

If 2 people had a 1% unbalance between positive and negative charges in their bodies, and stood 1 meter away from each other, they would feel an attractive force towards each other equivalent to the weight of this planet (The Feynman Lecture on Physics).

Electricity was not even know in the past (before VI BC).The history of electricity began in the 6th century BC when people noticed the unusual properties of amber (a tree resin) that when rubbed in wool or cat skin,it could attract objects.

This phenomenon could only be understood when the electron was discovered in 1896, by the English physicist J.J. Thomson. Wool has loose electrons, which pass on to the amber when it is rubbed against it. This way the piece of amber acquires an excess of electrons, which are negative charges, and as a result becomes negatively charged. This manner of acquiring charge is called charging by friction.

Like charges repel and opposite charges attract each other.

The amount of charge present is measured in coulombs (C). The minimum amount of charge that can exist is equivalent to 1.6 10-19 C, which is the charge of electrons and protons.

The table below shows some typical values:

Charge per bit in computer memory 10-13 C
Flow of charge in lightning 1 to 100 C