# deduce ohm’s law by elementary ideas and hence write an expression for resistance and resistivity

Umakant biswal
5349 Points
6 years ago
dear malavika
the elementary ideas of ohms law states that potential diffrence across a conducter is directly proportional to current passing through the conducter when physical condition will not change .
so, v is directly prop to i
and v/i = constant ( R )
where r is constant and known as resistance of the conducter , resistance is directly prop to the length and inversely prop , to the area of the cross section .
therefore ,
R is directly prop to l/a
on removing the sign of proportionality we get
R = rho *l /a , where rho is the resistivity
R will depend on nature of conducter ,
now , I = neAvd (vd is drift velocity )
and n is no of electrons present in unit volume of conducter .
so, vd = eET/ m
putting the value of vd in abvove equation we get
I = neA * eET/m
further , we know that
E = v/l so, I= neA * evt/ml
again , V/I = R = ml/nesquare a *t
and rho = R *a/l = m / n esquare t
these are the required expression
HOPE IT CLEARS
REGARDS