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Category
Electrostatics
Summary
Electrostatics is a branch of physics that studies slow-moving or stationary electric charges.
Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for amber, ἤλεκτρον (), was thus the source of the word 'electricity'. Electrostatic phenomena arise from the forces that electric charges exert on each other. Such forces are described by Coulomb's law.
There are many examples of electrostatic phenomena, from those as simple as the attraction of plastic wrap to one's hand after it is removed from a package, to the apparently spontaneous explosion of grain silos, the damage of electronic components during manufacturing, and photocopier & laser printer operation. Electrostatic forces play a large role at the nanoscale; for instance, the force between an electron and a proton, which together make up a hydrogen atom, is about 36 orders of magnitude stronger than the gravitational force acting between them. Because they are large at small scales, Coulomb forces between electrons and the positively charged nuclei play a very large role in how atoms and molecules behave.
Coulomb's law
Coulomb's law states that:
'The magnitude of the electrostatic force of attraction or repulsion between two point charges is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance between them.'
The force is along the straight line joining them. If the two charges have the same sign, the electrostatic force between them is repulsive; if they have different signs, the force between them is attractive.
If is the distance (in meters) between two charges, then the force (in newtons) between two point charges and (in coulombs) is:
where ε0 is the vacuum permittivity, or permittivity of free space:
The SI units of ε0 are equivalently A2⋅s4 ⋅kg−1⋅m−3 or C2⋅N−1⋅m−2 or F⋅m−1. The Coulomb constant is:
A single proton has a charge of e, and the electron has a charge of −e, where,
These physical constants (ε0, ke, e) are currently defined so that e is exactly defined, and ε0 and ke are measured quantities.
Official source
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