1012 Direct Current and Transient Analysis
I often say that when you can measure what you are speaking about, and express it in
numbers, you know something about it; but when you cannot express it in numbers,
your knowledge is of meager and unsatisfactory kind.
Lord Kelvin2.1 Introduction ...............................................................................................................
This chapter deals with the basic concepts and principles of electricity as well as the
analysis of simple electric circuits. A brief and compressed history of electricity is also
presented to introduce the reader to how this important fi eld of science and engineering
evolved over time.
The simplest manifestation of electricity in nature is the phenomenon of magnetism and
static electricity. Static electricity was fi rst observed by the ancient Greeks, and back then
they called this phenomenon elektron. The curious Greeks observed and studied the effects
of elektron, but no written records about the subject exist.
The fi rst recorded observations about electricity and magnetism date back to Thales
(640–546 BC), a famous philosopher and mathematician who lived on the west coast
of Asia Minor. Years later, the Chinese military commanders, during the Hun dynasty
(AD 206–220) are believed to have used the magnet’s properties to implement the fi rst
compass to indicate direction. It took about 900 years for the Europeans to incorporate the
compass in navigation. No signifi cant recorded scientifi c progress was made in electric-
ity and magnetism until the 1600s, when William Gilbert (1540–1603), Queen Elizabeth’s
physician, recorded experiments he performed with magnetic materials. He thought that
magnetism could have healing effects on the human body.
Probably the fi rst major modern scientifi c contribution was the Leyden jar developed by
Pieter van Musschenbrock and Benjamin Franklin. The jar was a device capable of storing
an electric charge (static electricity), which could be discharged producing an electric arc
or spark, thus emulating lighting.
Years later, it was discovered that lightning was in essence an electric discharge. The
most important scientifi c contributions occurred during the late 1700s through the late
1800s, when the effects of electricity and magnetism were observed, recorded, and seri-
ously studied. Concepts and principles once understood, tested, and proven became rules,
laws, and theories.
A number of electric units bear the name of those early pioneers, such as
Coulomb. After Charles Coulomb (1736–1806), Frenchman; observed, measured,
and quantized the amount of electricity (electric charge)
Ampere. After Andres Maria Ampere (1775–1836), Frenchman; studied the current
induced by a magnetic fi eld