Define Resistance and Conductance | SI Unit , Dimensions
Electric Resistance :
Resistance of a conductor is the opposition offered by the conductor to the flow of electric charge in the conductor.
Resistance of a conductor is defined as the ratio of the potential difference across the ends of the conductor to the current flowing through it.
That is,
$R = \frac{V}{I}$
S.I. unit of resistance :
It's S.I unit is ohm ($\Omega$)
$1 \text{ ohm } (\Omega) = \frac{1 \text{ volt } (V)}{1 \text{ ampere } (A)} \quad \text{ or } 1 \Omega = 1 VA^{-1}$
Definition of 1 ohm:
Resistance of a conductor is said to be 1 ohm, if current of 1 A flows through it, when potential difference of 1 V is applied across it.
Dimensional formula of resistance:
$[R] = \frac{[V]}{[I]}$
$[R]= \frac{[\text{Work}]}{[\text{Charge}] \times [\text{Current}]}$
$[R]=\frac{[\text{Work}]}{[\text{Current}] \times [\text{Time}] \times [\text{Current}]}$
$= \frac{[ML^2T^{-2}]}{[A^2T]}$
$= [ML^T^{-3}A^{-2}]$
Conductance:
Conductance of a substance is equal to the inverse of its resistance.
That is,
$G = \frac{1}{R}$
S.I. unit of conductance
ohm$^{-1}$ ($\Omega^{-1}$) or mho or siemen (S).
Dimensions of Conductance,
$[G] = \frac{1}{[R]} = [M^{-1}L^{-2}T^3A^2]$
Note :Conductance of a substance is also denoted by letter S.