102 Practical MATLAB® Applications for Engineers
Volt. After Count Alexander Volta (1747–1827), Italian; developed the voltaic cell
Ohm. After Georg Ohm (1787–1854), German; developed a relationship among the
current, voltage, and resistance in an electric circuit
Faraday. After Michael Faraday (1791–1867), Englishman; developed the basis of the
electromagnetic theory
Hertz. After Heinrich Rudolph Hertz (1857–1894), German; experimented with elec-
tromagnetic wavesTwo additional names are associated with the early developments of electric theories and
discoveries, and their work constitutes the basis of electric circuits. They are:
James Clark Maxwell (1831–1879), Scottish. Maxwell developed the relationship between
electricity and magnetism, as well as the electromagnetic theory of light (1862).
Gustav Robert Kirchhoff (1824–1887), Russian. Kirchhoff formulated the basic circuit
laws (the network current and voltage laws).The theoretical fundamentals of electricity and magnetism were observed, studied, and
fi rmly established, predominantly by European physicists, engineers, and mathematicians.
American scientists and engineers are distinguished as the great inventors, patent hold-
ers, and industrialists who brought the electric discoveries into the market place. The most
important Americans, just to mention a few, are
Thomas Edison (1847–1931)
Alexander Graham Bell (1847–1922)
Lee De Forest (1873–1961)Today we know that electricity is produced by electrons. An electron is the smallest unit
of electric charge, and its quantity is known as “1 esu.” An electron is not easily found in
nature, but it can be generated, and it constitutes the most important source of energy in
modern societies. In its simplest version, the concepts of current and voltage constitute the
bases of electricity.
Let us defi ne current and voltage using the simplest possible terms. Current is the fl ow
(movement) of electrons, whereas voltage is the force that makes this fl ow possible.
This chapter deals with DC electrical systems and transients. The term “DC” is an abbre-
viation of direct current, which refers to electrical sources that employ unidirectional cur-
rent. These sources of voltage or current provide a fi xed or constant output.
A current that varies with respect to time reversing directions periodically is called
alternating current, abbreviated as “AC,” and is the subject of Chapter 3.
DC voltage sources consist of batteries, generators, and power supplies. These devices
employ different technologies and modes of operations, but the end result is to supply
a constant terminal voltage, regardless of the current demand and load connected to its
terminals.
A DC current source is analogous to a voltage source in the sense that it supplies a con-
stant current fl ow, whereas the voltage demand may vary across its terminals.
DC is produced either by a voltage or current source that delivers a constant output,
denoted mathematically as e(t) = E V (volts) or i(t) = I A (amp) respectively, and the electrical
responses (steady state) in any of its branches of an electrical network are also constant.