Law of Coulomb (electrostatic)

See also: Law of Coulomb

In electrostatic, the law of Coulomb expresses the electric force \ vec {F} _ {1 \ rightarrow 2} \, exerted by a electric Charge q_1 \, placed in a point M_1 \, on a load q_2 \, placed in a point M_2 \, . This law is expressed in vectorial form by the following formula:

\ vec {F} _ {1 \ rightarrow 2} = \ frac {q_1 q_2} {4 \ pi \ epsilon_0 {\|\ vec {R} _ {12} \|} ^2}. \ frac {\ vec {R} _ {12}} {\|\ vec {R} _ {12} \|}
where
  • ε 0=8,854·10-12 F·m-1 is a universal constant called electric permittivity of the vacuum, and
  • \ vec {R} _ {12} = \ overrightarrow {M_1M_2} is the Vecteur position which connects the first body to the second.

In the system of units C.G.S. the law is written more simply

\ vec {F} _ {1 \ rightarrow2} = \ frac {q_1q_2} {\|\ vec {R} _ {12} \|^3} {\ vec {R} _ {12}} \,

with the lengths this time expressed in centimetres (cm) and them loads in electrostatic unit (esu).

NB: the law is not valid for loads moving but only in one reference frame where they are fixed.

See too

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