Write limitations of Ohm's law.

Explanation

`rArr` For certain materials and devices used in day to day life voltage (V) and current (I) are not proportional to each other. So in such case Ohm.s law is not obeyed. But,
`rArr` (a) V and I are not proportional to each other.

In graph, dotted line part shows that Ohm.s law is obeyed. Where as Continuous curve of the graph shows that Ohm.s law is not obeyed.
`rArr` When current flows through conductor partial Joule heat is produced. Hence, when conductor is heated its resistance increase Hence, for such material V `rarr` I graph will be continuous curve.
Example : Diode, Transistor.
(b) Relation between I and V depend on polarity of V. Hence, for same positive or negative value of voltage different current value are obtained.
Example : PN junction diode.
`rArr` In graph shown for positive and negative value of voltage and current scales are different.

(c) I `rarr` V relation is not one-one function . one value of current there are more that one value of voltage . for example GaAs exhibit such behaviour.
`rArr` figure shows I `rarr` V graph for GaAs. In such graph `(Delta V)/(Delta I)` is used to obtain resistance.