Coulomb’s LawCoulomb’s Law

Coulomb’s law can be applied to any point charges. It is given by:

$F=frac{Qq}{4Pi varepsilon _{o}r_{2}}$

Since $E=frac{F}{Q}$ , it follows that, for a point charge, the electric field strength is given by:

$E=frac{Q}{4Pi varepsilon _{o}r_{2}}$

Gravitational and electric fields show some similarities and differences:

Gravitational Electric

Force is between	Objects with mass	Objects with charge
Constant of proportionality	G Applies to all materials	ε depends on the medium in which the field exists
Field strength in a radial field	Nkg^-1 or ms^-2 Vector	NC^-1 or Vm^-1 Vector
Definition of Field Strength	Force per unit mass	Force per unit charge
Force in a radial field	Always attractive Vector	Can be attractive or repulsive Vector
Potential in a radial field	Jkg^-1 Scalar Always less than zero.	JC^-1 Scalar Sign depends on charges
Definition of Potential	Work done in bringing a unit mass from infinity to the point in the field.	Work done in bringing a unit positive charge from infinity to the point in the field.
Potential Energy	E_p = Fm	W=VQ