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 Kelvin 2.1 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.
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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.
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No signifi cant recorded scientifi c progress was made in electricity 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.
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