current electricity Flashcards
define current
current at time t is defined as the value of the ratio of q to t in the limit of t tending to 0
what is ohm’s law
imagine a conductor carrying a current i and let v be the potential difference b/w the ends of the conductor then ohm’s law states that
v is proportional to i
or
v = i*r
where r is proportionality constant and is called resistance of the conductor
what is current density
current per unit are is called current density and is denoted by J
its SI unit is A/m^2
what is relaxation time
Time interval between two successive collisions of electrons in a conductor, when current flows is relaxation time
define drift velocity
electrons moves with an average velocity which is independent of time although it is accelerated
this phenomenon is known as drift and velocity is called drift velocity
define mobility
it is defined as the magnitude of the drift velocity per unit electric field
what are limitation of ohm law
1 V ceases to be proportional to I
2 the relation b/w V and I depends on the sign of V
3 relation b/w V and I is not unique
state kirchhoff junction rule
at any junction the sum of the currents entering the junction is equal to the sum of current leaving the junction
state kirchhoff loop rule
the algebraic sum of the changes in the potential around any closed loop involving resistor and cells is zero
