**Chapter-3|Current Electricity| NCERT 12th Physics:**

**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.

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

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**(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.

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