, developed in the 1780s by French physicist Charles Augustin De Coulomb , may be stated as follows:
''The magnitude of the electrostatic Force between two point Electric Charge s is directly Proportional to the product of the magnitudes of each charge and inversely proportional to the square of the distance between the charges.''
If one is interested only in the magnitude of the force, and not in its direction, it may be easiest to consider a simplified, Scalar version of the law:
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:
is a constant called the
Permittivity Of Free Space .
This vector equation indicates that opposite charges attract, and like charges repel. When
is negative, the force is attractive. When positive, the force is repulsive.
Below is a graphical representation of Coulomb's law, when
. The vector
is the force experienced by
. The vector
is the force experienced by
. Their magnitudes will always be equal. The vector
is the displacement vector between two charges (
and
).
In either formulation, Coulomb's law is fully accurate only when the objects are stationary, and remains approximately correct only for slow movement. These conditions are collectively known as the
Electrostatic Approximation . When movement takes place,
Magnetic Field s are produced which alter the force on the two objects. The magnetic interaction between moving charges may be thought of as a manifestation of the force from the electrostatic field but with
Einstein 's
Theory Of Relativity taken into consideration.
The accuracy of the exponent in Coulomb's Law has been found to differ from two by less than one in a billion by measuring the electric field inside a charged conducting shell.
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