General form of Ohm’s law:
At a constant temperature potential difference across a conductor is directly proportional to the current passing through it
V α I V = RI
Ohm’s law is material dependent because it is defining resistance of the material. Those which obeys ohm’s law and are known as ohmic or linear conductor, otherwise non-ohmic or nonlinear conductor.Proof: Current density (J) α E (Applied electric field)
J α E
j = σE
σ = Conductivity
We know that
σ = 1/ρ
R = ρ * 1/A
ρ = RA/l
1/ρ = l/RA = σ
J = 1/A, E = v/l
\(\frac{I}{A}=\frac{\rho }{RA}*\frac{V}{l}\) \(I=\frac{V}{R}\Rightarrow V=IR\)Limitations:
- It is valid only at constant temperature.
- It can be applied only to bi – lateral elements [linear elements].