When a number of impedances are connected together to form a system that consists of set(s) interconnected circuits performing specific or assigned functions, it is called a “network” or “Circuit”. An “Electrical network” with which the present text is concerned, is a combination of numerous electric elements (e.g., resistance (R), inductance (L), capacitance (C) etc.)
A network element is a component of a circuit having different characteristics as described below:
Linear and Non-Linear Elements
A linear element shows linear characteristics of voltage vs current. Simple resistors, inductors and capacitors are linear elements and their resistances inductances and capacitances do not change with a change in applied voltage or the circuit current.
For a non-linear element, the current passing through it does not change linearly with the linear change in applied voltage at a particular frequency. Semiconductor devices are usually example of non-linear elements.
Active and passive elements
If a circuit elements has the capability of enhancing the energy level of a signal passing through it, it is called an active element.
Vacuum tubes and semiconductor devices (such as transistors op. amps. etc.) are active elements. On the other hand, resistors, inductors, capacitors, thermistors etc. are passive elements as they do not have any intrinsic means of signal boosting.
Unilateral and Bilateral Elements
If the magnitude of the current passing through an element is affected due to change in the polarity of the applied voltage, the element is called unilateral element. On the other hand, if the current magnitude remains the same even if the applied e.m.f.’s polarity is changed, it is called a bilateral element. Unilateral elements offer varying impedance with variations in flow of current while bilateral elements offer same impedance irrespective of flow of current. A resistor, inductor, capacitor are bilateral network elements while diode, transistor are unilateral elements.