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

Since , it follows that, for a point charge, the electric field strength is given by:

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 |