Explanation:
Ohmic Behavior:
If the current "I" produced in a conductor due to voltage "V" applied across it, is directly proportional to that voltage while the resistance of the conductor is same/constant, the material is said to be ohmic material or possessing ohmic behavior. If the resistance of a conductor doesn't remain the same due to heat, material property or any other reason, non-ohmic behavior will be observed.
Thermal Expansion vs Ohmic/Non-ohmic property:
For a linear conductor, thermal expansion (may be due to heat produced in result of current flow) increases length of the material due to which its resistance increases directly. Whenever the resistance increases during the flow of a current, the non-ohmic behavior arises.
R = ρL/A
where,
R=Resistance of conductor
ρ=Resistivity of material
L=length of conductor
A=Cross-sectional area of the conductor.
But,
usually this change in length and consequently change is resistance is very minor, so ignoring this change, the non-ohmic property of material will be minor too.
Non-Ohmic Property:
Current flows in a conductor due to flow of electrons in it. When these flowing electrons interacts with other particles (electron or atoms' nucleus) heat is produced. Due to this heat, atomic particles vibrates with more speed resulting in more hindrance/resistance in the flow of electron i.e. Resistance of material is now increased, so this will result in Non-ohmic behavior because now for the same value of applied voltage V, the flow of electron (Current) will be lesser. This will result in deviation from straight line graph as well (picture is attached)
