Ohm’s law

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

  

Limitations:

• It is valid only at constant temperature.
• It can be applied only to bi – lateral elements [linear elements].