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Table Of Contents  CertiGuide to A+ (Core Hardware)
 9  Chapter 0000:  The Start of the PC
      9  V  Electricity

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Cycles Per Second (CPS)

So far, we know that electricity can flow as AC or DC. Who said the flow must be continuous? It doesn't have to be. Further, there is no law of nature that demands that voltage remain constant. It is technically possible to vary the number of oscillations between positive and negative sweeps in AC, and to vary the amount of DC current or even turn it on and off to create pulses.

When you have an AC current the number of sweeps between positive and negative is measured in Cycles Per Second (CPS). Electricity in North America is delivered at 60 CPS, with the pressure of 120 volts. Sometimes this is expressed as 120VAC. In Europe, the standard is 50 CPS and 240VAC. In computers, we describe CPS using Hertz, or Hz. A device that operates at 1000 CPS is running at 1KHz.

[spacer]Intelligent Life

Vary either voltage or the CPS, a process known as modulation occurs. This is how radio and TV work. The stream is more or less continuous and is considered an analog signal.


Taking DC and turning it on and off, or, pulsing the voltage is the basis for a digital signal. For example, 5VDC could be a one, and 1VDC or even a negative voltage could signify a zero.

With the basics of electrical properties complete, let's look at a few electronic components.

[spacer]The Numerous Wonders of Electricity

The above example does not cover how AC and DC can co-exist on the same wire, or other more advanced topics, such as saw tooth waveforms. This book will not cover more esoteric concepts such as skew (which can be a real challenge in SCSI devices). The intent of this book is to prepare the reader for A+ certification. We have more than covered electricity as a testable concept in this chapter. However we encourage any reader who wishes to know more to start with Getting Started in Electronics. Forrest M Mims III, available at Radio Shack.



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Multimeters
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Resistor
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