Unilateral and bilateral elements.
Unilateral element :
When a reversal of the applied voltage happens then at that moment the VI characteristics changes which is a unilateral element.
For example: Diode
As the first values of Z = 4 / 4 = 1 and another Z = -1.5 / -1 = 1.5.
Hence it is a unilateral element.
Here it is a non-linear graph as it does not satisfy all values of x.
Bilateral element:
It is defined as the elements through which the current is independent of the polarity of the applied voltage.
Here the VI characteristics will not be affected by the voltage when it is reversed.
Examples of bilateral elements are resistors, inductors, and capacitors.
Take this graph, here we have a straight line R at point A will be 1 ohm as well as at point B we have Z as 1 ohm.
R = V / I = 4 / 1 = 1 ohm
Hence it is bilateral graph.
Time variant and time-invariant:
An element is said to be a time-variant whose VI characteristics change concerning time.
An element is said to be a time-invariant whose VI characteristics do not change concerning time.