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

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

Grade:12

1 Answers

Umakant biswal
5359 Points
4 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 

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