Electric circuit theory and electromagnetic theory are the two fundamental theories upon which all branches of electrical engineering are built. Many branches of electrical engineering, such as power, electric machines, control, electronics, communications, and instrumentations, are based on electric circuit theory. Therefore, the basic electric circuit theory is the most important course for an electrical engineering student and always an excellent starting point for a beginning student in electrical engin eering education. Circuit theory is also a valuable to students specializing in other branches of the physical sciences because circuits are good model for the study of energy systems in general, and because the applied mathematics, physics, and topology involved.
In electrical engineering, we are often interested in communicating or transferring energy from one point to another. To do this requires an interconnection of electrical devices. Such interconnection is referred to as an electric circuit and each component of the circuit is known as an element.
A simple electric circuit is shown in Fig. 2.1. It consists of three basic components: a battery, a lamp and connecting wires. Such a simple circuit can exist by itself; it has several applications, such as a torch light, a search lights and so forth.