Linear and Non Linear Elements

Linear Element:

An element or a system is said to be linear if it obeys the principles of additive and homogeneity. For a linear element the current passing through it is always proportional to the voltage across it. Practicallyperfect linear elements are seldom found and show some non-linearity, but approximations are made for simplifying the computations.  The V-I characteristics of linear elements pass through the origin.

Homogeneity Property:

When I₁ is the circuit current for applied voltage V₁, then for applied voltage αV₁ the circuit current should be αI₁. Where α is a constant. 

homogeneity

Additive Property:

If I₁ is the current for applied voltage V_1, I₂ is current for Voltage V₂ then for applied voltage V₁+V₂ the current should be I₁+I₂.

Examples: ohmic resistances, conductors etc.

Additivity

Non-linear Elements:

All the elements which are not linear and do not obey the principles of homogeneity and additive properties are called non-linear elements. A nonlinear element doesn't obey ohm’s law.

Examples: diodes and other semiconducting materials, non-linear resistors etc.

Also Read

Classification of circuit elements
Active and passive elements
Unilateral and bilateral elements
lumped and distributed elements