19.1 Coulomb's Law
The force ( f ) between two electric charges
'q1' and 'q2' separated by the distance 'r' between them
acts along the line joining them. Its magnitude is proportional to each charge and inversely proportional to
the Square of the distance between them.
where 'K' is constant of proportionality, whose value depends on the unit of charge chosen and the
property of medium separating the charges. In S.I system and in vacuum (for all practical purposes, in air),
Vector form of Coulomb's law
Note : If q1 and q2 are unlike charges, then a negative sign should be put on the R.H.S; however it can
be absorbed in the sign to be used for the charges themselves.
If we have a system of charges (discrete) then the resultant force is the vector sum of the forces on
a charge due to the rest of the charges.