ABSTRACT
A discussion of electric circuits logically begins with the definitions of the two basic circuit variables, namely current and voltage, and their relation to electric energy and power. Physically, an electric circuit is an interconnection of circuit elements of various types, such as sources of electric energy, resistors, capacitors, and inductors. Power-absorbing elements are simulated by resistors, whereas power-delivering elements are simulated by dc sources. The values of practical circuit elements may be considered constant over a limited operating range and may change over a prolonged period. Under the influence of the power supply connected in the external circuit between the anode and cathode, electrons flow in the power supply from the positive terminal to the negative terminal, up a potential energy gradient, because the cathode is at a negative voltage with respect to the anode. Dependent sources are most commonly encountered in the equivalent circuits of electronic devices such as transistors and operational amplifiers.
