· Like charges repel and unlike charges attract
· The total charge in the universe is conserved
· Charge is quantized. Total charge in an object q = ne where n = 0,1,2,3… and e is electron charge.
· Coulomb’s law in vector form: (r ^ is unit vector along joining q1, q2)
· For continuous charge distributions, integration methods can be used.
· Electrostatic force obeys the superposition principle.
· Electric field at a distance r from a point charge:
· Electric field lines starts at apositive charge and end at a negative charge or at infinity
· Electric field due to electric dipole at points on the axial line :
· Electric field due to electric dipole at points on the equatorial line:
· Torque experienced by a dipole in a uniform electric field:
· Electrostatic potential at a distance r from the point charge:
· Electrostatic potential due to an electric dipole:
· The electrostatic potential is the same at all points on an equipotential surface.
· The relation between electric field and electrostatic potential:
· Electrostatic potential energy for system of charges is equal to the work done to arrange the charges in the given configuration.
· Electrostatic potential energy stored in a dipole system in a uniform electric field:
· The total electric flux through a closed surface : ΦE = Q/ε0 where Q is the net charge enclosed by the surface
· Electric field due to a charged infinite wire :
· Electric field due to a charged infinite plane :
· Electric field inside a charged spherical shell is zero. For points outside:
· Electric field inside a conductor is zero. The electric field at the surface of the conductor is normal to the surface and has magnitude E = σ/ε0 .
· The surface of the conductor has the same potential, at all points on the surface.
· Conductor can be charged using the process of induction.
· A dielectric or insulator has no free electrons. When an electric field is applied, the dielectric is polarised.
· Capacitance is given by C = Q/V .
· Capacitance of a parallel plate capacitor: C = εA / d
· Electrostatic energy stored in a capacitor: U = 1/2 CV2
· The equivalent capacitance for parallel combination is equal to the sum of individual capacitance of capacitors.
· For a series combination: The inverse of equivalent capacitance is equal to sum of inverse of individual capacitances of capacitors.
· The distribution of charges in the conductors depends on the shape of conductor. For sharper edge, the surface charge density is greater. This principle is used in the lightning arrestor
· To create a large potential difference, a Van de Graaff generator is used