Electrostatics
The fundamental equations of electrostatics are linear equations,
(SI units), 
(Gaussian units).The principle of superposition holds.
The electrostatic force on a particle with charge q at position r is F=qE(r).
. f is the electrostatic potential.
Important formulas:
The field at r due to a point charge at r?:
(Omit the factor 
to obtain the corresponding expressions in Gaussian units.) The field of a charge distribution:
(We consider volume, surface, and line charge distributions and point charges.)
The potential at r due to a point charge at r?:
The potential of a charge distribution:
Gauss? law:
(SI units), 
(Gaussian units).In situations with enough symmetry, Gauss? law alone can be used to find E.
The electrostatic energy of a charge distribution:
or, for a continuous charge distribution,
(SI units), 
(Gaussian units).The field of a dipole at the origin:
The potential of a dipole at the origin:
The force on a dipole:
The torque on a dipole:
The energy of a dipole in an external field:
 | E=0 inside. |
| r =0 inside. |
| Any excess charge resides on the surface. |
| E on the surface is perpendicular to the surface. |
|  (SI units),  (Gaussian units), just outside the surface. |
The polarization 
is defined as the dipole moment per unit volume. The total charge density is due to free and to bound (polarization) charges.
.
(SI units), 
(Gaussian units).For linear, isotropic, homogeneous (lih) dielectrics we have
, 
,
, 
,
, 
.Hope this will help everyone to do their revision.......
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(SI units), 
, 
, 
(Gaussian units),
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