Non ohmic conductors are said to be the conductors that do not obey Ohm's Law. The V-I graph for them is not a straight line unlike ideal ohmic conductors.
According to me Ohm's Law states: The voltage across a conductor is directly proportional to the current in it given that other factors such as temperature remain constant. ie.
I have also read that change in temperature due to heat dissipated is also a reason for varying V/I values for non ohmic conductors. My question is that,given this, how can we say that a conductor doesn't obey Ohm's law. Shouldn't everything be having a constant voltage to current ratio at a given point in time (or an infinitesimal time interval). Similarly shouldn't the resistance be then defined to be the derivative of voltage with respect to current?