# Phase and group speeds

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• ### Principles of Modern Physics

This book is intended as a general introduction to modern physics for science and engineering students. It is written at a level which presurnes a prior tull year’s course in classical physics, and a knowledge of elementary differential and integral calculus. The material discussed here includes probability, relativity, quantum mechanics, atomic physics, statistical mechanics, nuclear physics and elementary particles.

• ### HARMONICS AND POWER SYSTEMS by Taylor & Francis Group

In a normal alternating current power system, the voltage varies sinusoidally at a specific frequency, usually 50 or 60 hertz. When a linear electrical load is connected to the system, it draws a sinusoidal current at the same frequency as the voltage (though usually not in phase with the voltage). When a non-linear load, such as a rectifier, is connected to the system, it draws a current that is not necessarily sinusoidal. The current waveform can become quite complex, depending on the type of load and its interaction with other components of the system.