Limitations of Ohm's Law

The devices which do not obey Ohm's law are called non ohmic devices, such a vacuum tube.

The relation V/I=R is valid for both ohmic and non ohmic devices.

For ohmic conductors value of R is constant. For non ohmic devices, value of R is not constant.

The limitations of Ohm's Law given below.

(I). Potential difference may vary non-linearly            with current.

(II). The variation of current with potential difference may depends upon sign of potential difference applied.

(III). The relation between potential difference and current is not unique i.e there is more than one value of V for the same current I.