Electric Charges and Fields
Electrostatics is the branch of physics which deals with electric charges at rest. Electric charge is the fundamental physical quantity due to which electrical and other related effects are produced in matter. There are two types of charges: positive charge and negative charge. A simple apparatus to detect charge on a body is the gold-leaf electroscope. Conductors allow electric current to pass through them. Insulators do not allow electric current to pass through them. A body can be charged by induction or conduction. Electric charges add up like real numbers.
Total charge of isolated system remains conserved. Electric charge is always an integral multiple of e.
When two charges are placed near each other, they experience a force which is defined by Colulomb’s law. Colulomb’s law states that force experienced by charges is directly proportional to product of two charges and inversely proportional to square of distance between them. Force on any charge due to number of other charges is the vector sum of all the forces on that charge, taken one at a time. The force experienced is due to Electric field of charges. Electric field is the region around a charge in which its electrical influence can be realized. Electric field around a charge can be represented by Electric field lines. The number of electric lines of force passing through a surface in an electric field is called Electric Flux.
A pair of equal and opposite point charges separated by a distance forms an electric dipole. Electric dipole moment is defined as the product of the magnitude of either charge and distance between them. The field due to dipole is the space around the dipole in which the electric effect of the dipole can be experienced. The field is different on axial line as compared to field on equatorial line of an electric dipole. An electric dipole placed in an external uniform electric field forms a couple which exert a torque.
The electric field due to uniformly charged bodies can be found using Gauss’s Law. Gauss’s Law states that, total electric flux phi, through a closed surface (S) is equal to one upon epsilon knot times the total charge (q) enclosed by the surface. This law holds good for any closed charged surface of any shape.