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Sinusoids and Phasors

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Sinusoids and Phasors

He who knows not, and knows not that he knows not, is a fool—shun him. He who knows not, and knows that he knows not, is a c hild—teach him. He who knows, and knows not that he knows, is asleep—wake him up. He who knows, and knows that he knows, is wise—follow him.

—Persian Proverb

Enhancing Your Skills and Your Career

ABET EC 2000 criteria (3.d), “an ability to function on multi‑disciplinary teams.”

The “ability to function on multidisciplinary teams” is inherently critical for the working engineer. Engineers rarely, if ever, work by themselves. Engineers will always be part of some team. One of the things I lik e to remind students is that you do not ha ve to like everyone on a team; you just have to be a successful part of that team.

Most frequently, these teams include indi viduals from a v ariety of engineering disciplines, as well as individuals from nonengineering disciplines such as marketing and finance.

Students can easily de velop and enhance this skill by w orking in study groups in every course they take. Clearly, working in study groups in nonengineering courses, as well as engineering courses outside your discipline, will also give you experience with multidisciplinary teams.

Photo by Charles Alexander

Historical

George Westinghouse. Photo © Bettmann/Corbis

Nikola Tesla (1856–1943) and George Westinghouse (1846–1914) helped establish alternating current as the primary mode of electricity transmission and distribution.

Today it is obvious that ac generation is well established as the form of electric power that makes widespread distribution of electric power efficient and economical. However, at the end of the 19th century, which was the better—ac or dc—w as hotly debated and had e xtremely outspoken supporters on both sides. The dc side was led by Thomas Edison, who had earned a lot of respect for his many contributions. Power generation using ac really be gan to b uild after the successful contrib utions of Tesla. The real commercial success in ac came from Geor ge Westinghouse and the outstanding team, including Tesla, he assembled. In addition, tw o other big names were C. F. Scott and B. G. Lamme.

The most significant contribution to the early success of ac w as the patenting of the polyphase ac motor by Tesla in 1888. The induction motor and polyphase generation and distrib ution systems doomed the use of dc as the prime energy source.

Learning Objectives

By using the information and exercises in this chapter you will be able to:

    1. Better understand sinusoids.
    1. Understand phasors.
    1. Understand the phasor relationships for circuit elements.
    1. Know and understand the concepts of impedance and admittance.
    1. Understand Kirchhoff’s laws in the frequency domain.
    1. Comprehend the concept of phase-shift.
    1. Understand the concept of AC bridges.