Electric Circuits 8th Edition 38

# Electric Circuits 8th Edition 38 - tion. Recall from basic...

This preview shows page 1. Sign up to view the full content.

14 1.6 Power and Energy Power and energy calculations also are important in circuit analysis. One reason is that although voltage and current are useful variables in the analysis and design of electrically based systems, the useful output of the system often is nonelectrical, and this output is conveniently expressed in terms of power or energy. Another reason is that all practical devices have Iimitations on the amount of power that they can handle. In the design process, therefore, voltage and current calculations by tlemselves are not sufficient. We now relate power and ene.gy to voltage and curent and at the same time use the power calculation to illustrate ttre passive sEn conven-
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: tion. Recall from basic physics that power is the time rate of expending or absorbing energy. (A water pump rated 75 kW can deliver more lite\$ per secord than ore rated 7.5 kW.) Mathematically, energy per unit time is er-Dressed in the form of a derivative. or (1.3) ,:'H,., Definition of power > Power equation > the power rn watts, the energy in joules, the time in sconds. Thus 1W is equivalent to 1 J/s. The powei associated with the flow of charge follows directly from the definition of voltage and current in Eqs.1.1and 1.2,or (1.4) aw / aw\( aq\ dt \ dq l\dt J' p : t}le power in watts, 1) = the voltage in volts, i : the curent in amperes,...
View Full Document

## This note was uploaded on 07/05/2010 for the course EE 100 taught by Professor Boser during the Spring '07 term at University of California, Berkeley.

Ask a homework question - tutors are online