A collection of devices such as resistors and sources in which terminals are connected together by connecting wires is called an electric circuit. These wires converge in nodes, and the devices are called branches of the circuit, as shown in figure 1.5.
The general circuit problem is to find all currents and voltages in the branches of the circuit when the intensities of the sources are known. Such a problem is usually referred to as circuit analysis.
Remarks -- While the current in a resistor has a fixed relationship with the voltage across it, the current flowing in a voltage source, or the voltage across a current source, is theoretically unrestricted and can assume whatever value governed by the external circuit.
Figure 1.5: Part of an electric circuit