Current_Electricity

[pic] [pic] [pic] When two ends of a conductor are maintained at different potentials ,charges begin to flow from higher potentials to lower potentials ,which constitute electric current Definition of Electric Current I = q/t = dq/dt i.e. the time rate of flow of electric charge is called electric current. SI unit of electric current I = 1 coulomb / 1second = 1 Ampere = 1 A (Named after the French scientist, Andre Marie Ampere,1775-1836) Smaller Units of electric current 1milli ampere(1mA) = 10-3 A 1micro ampere(1µA) =10-6 A Conventional Direction of Electric Current [pic] Actual direction of flow of electrons Electric current is a scalar quantity It has magnitude as well as direction but it is a scalar quantity, because it does not follow the law of vector addition. [pic] Electric current is a scalar quantity It has magnitude as well as direction but it is a scalar quantity, because it does not follow the law of vector addition. • Electric Potential Electric Potential at any point in an electric field due to a given charge is the amount of work done in carrying a unit positive charge from infinity to that point against electric field without producing acceleration. [pic] • Electric Potential Difference Electric potential difference between two points in an electric field is the amount of work done in carrying unit positive charge from one point to another against electric field without producing acceleration. [pic] Drift velocity of electrons When no electric field is applied [pic] [pic] U av = u1 + u2 + u3 + ………+un / n = o Drift velocity of electrons • When external electric field is applied [pic] F = -eE = ma a = -eE/m Vd = -eE/m . t Drift velocity of electrons & electric current Let, l= length of a conductor A= area of cross section n= number of electrons per unit volume E= external electric field applied V= potential difference vd= drift velocity i=neAvd Derivation of Ohms Law [pic] Resistance [pic] [pic] [pic][pic] [pic] ----------------------- +1 Q Q X Y