In a direct current (DC) circuit, or in an alternating current (AC) circuit whose impedance
is a pure resistance, the voltage and current
are in phase, and the following formula holds:
P = ErmsIrms
where P is the power in watts, Erms is the root-mean-square (rms) voltage in volts, and Irms
is the rms current in amperes. But in an AC circuit whose impedance consists of reactance
as well as resistance, the voltage and current are not in phase. This complicates the
determination of power.
In the absence of reactance, the product ErmsIrms
represents true power because it is
manifested in tangible form (radiation, dissipation, and/or mechanical motion). But when there is reactance in an AC circuit, the product ErmsIrms
is greater than the true power. The excess is called reactive power, and represents energy
alternately stored and released by inductors and/or capacitors. The vector sum of the true and reactive power is known as apparent power.
This was last updated in September 2005
Email Alerts
Register now to receive SearchCIO-MidMarket.com-related news, tips and more, delivered to your inbox.
By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States.
Privacy
More News and Tutorials
-
Backing up to local disk or tape can protect against the accidental destruction of a file but will do nothing to protect you when your facility suffers fire or flooding. Remote backup provides a better solution. This tip looks at two possibilities for remote backup: Choosing an outsourced remote backup service, or using software to do your own backups to an offsite facility.
-
Learn how attackers are using the widespread deployment of low-cost VoIP to leverage phishing attacks.
-
Is the government listening to your VoIP traffic? Can other companies spy on your WAN? It may sound like a paranoid conspiracy theory, but it's not that far out, technologically speaking. In this tip, Tom Lancaster looks at just how exposed your WAN traffic may be.
