**(A) Resistivity**

**j**= nq

**v**

_{d}where

**v**is the drift velocity.

_{d}ρ = E/j

This relationship is known as Ohm's law discovered by german physicist Georg Simon Ohm (1787-1854) in 1826.

^{22}) greater then that of metals.

^{-1}.

(B) Resistivity and temperature

(B) Resistivity and temperature

ρ(T) = ρ(T

_{0})[ 1 +α(T-T

_{0})]

where, ρ(T) and ρ(T

_{0}) are resistivities at temperature T and T

_{0}respectively and α is constant for a given material which also depends on temperature to a small extent. This constant α is known as temperature coefficent of resistivity.

**(C) Resistance**

E = ρj

where ρ is a constant independent of E.

E = V/l

If i is the current flowing inside the wire then current density is given by

j = i/A

putting these values in Ohm's law ρ = E/j we get

V = ρi (l/A)

or , V=Ri

where, R=ρ(l/A)

which is known as resistance of a given conductor.

R(T) = R(T

_{0})[1 + α(T - T

_{0})]

In this equation. R (T) is the resistance at temperature T and R(T

_{0}) is the resistance at temperature T

_{0}. The temperature coefficient of resistance α is the same constant that appears in case of resistivity.

**In the next post we'll do some worked examples related to this topic**