* Fundamental forces of nature :
(i) Gravitation,
(ii) Electromagnetic,
(iii) Nuclear,
(iv) Weak
* Relative strength 1 : 1036 : 1039 : 1034
* Charge is quantised, the quantum of charge is e = 1.6 × 10-19 C.
* The charge on the electron or proton denoted by e is the smallest charge that exists in nature. All other charges are integral multiple of this charge. (q = ne)
* When two bodies are rubbed against each other there is generally a transfer of electrons from one body to the other. A body which loses electrons is positively charged and the other negatively charged. If the body is an insulator, electric charge remains confined to the rubbed portion but in case of conductor it spreads out on the surface of the conductor.
* Electric field inside a charged conductor is zero. However there is electric field on the surface of conductor which is normal to the surface. In case of irregularly shaped conductor, the electric field E and surface charge density s vary from point to point (E = (s/Î0) At sharp points surface charge density and electric field have greater value. However potential at each point of the same conductor have equal value.
* Electric field lines which are tangent to electric field, originate from positive charges and end on a
negative charges. They are perpendicular to the surface of conductor (or any equipotential surface) but do not pass through conductor.
* Work done in a moving a point charge q from point A to point B independent of the path taken and is equal to q( VB - VA)
* A free stationary positive (negative) charge moves from higher (lower) to a lower (higher) potential.
* The value of dielectric constant ‘k’ is infinite for metals and one for vacuum.
* Work done in rotating a dipole is given by W = Uf - Ui = pE (cosqi - cos qf)
* An electric dipole always tries to align itself with the electric field because its potential energy in this configuration is minimum.
* For a charge moving in an electric field, gain (less) in kinetic energy is always equal to loss (gain) in potential energy.
Hence, {(1/2) mv2f - (1/2) mv2i} = - q(Vf - Vi)
* Electric field intensity due to a monopole (point charge) varies inversely as a square of the distance whereas in case of dipole it varies inversely as the cube of the distance.
* Potential of an isolated conductor is inversely proportional the dielectric constant of the medium.
* Potential energy of system having two point charges :
U = (1/4pÎ0)(q1q22/r)
|
|
