Electric Circuits 8th Edition 53

Electric Circuits 8th Edition 53 - diagram symbol for an B...

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2.2 ELectricat Resktance (ohmt Law) 29 the direction of the voltage drop across the resistor or in the direction of the voltage rise across the resistor, as shown in Fig. 2.6. If we choose the former, the rclationship between the voltage and current is ?r - iR, (2.1) .{ 0hm's taw r : the voltage in volts, i = the curent in amperes, R : the resistance in ohms, If we choose the second method, we must wnte where r,, j, and R are, as before, measured in volts, amperes, and ohms, respectively. The algebmic signs used iII Eqs. 2.1 and 2.2 are a direct conse- querce of the passive sign convention, which we introduced in Chapter 1. Equations 2.1 and 2.2 are known as Ohm's law after Georg Simon Ohm, a German physicist who established its validity early
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Unformatted text preview: diagram symbol for an B O resistor is shown in Fig.2.7. Ohm's law expresses the voltage as a function of the current. However, expressing the curcnt as a function of the voltage also is convenient. Thus, frcm Eo.2.1. u = -iR, \2.2) (2.3) 12.4) " = * " \2.5) i l ^ ' l r = i R r = , R Figure 2.6.q Two possibte r€ference choices forthe drrent and vottage atthe ternrinals of a resistor, and 8r} Flgure 2.7 d. The circuit symboLfor an 8 O rcsjstor. :1 or,fromEq.2.2, The reciprocal of the resistance is rcferred to as conductance, is sym-bolized by the letter G, and is measured in siemens (S).Thus An 8 O resjstor has a conductance value of 0.125 S In much of tie profes sional iiterature, the ur t used for conductance is the mho (ohm spelled back-ward), which is symbolized by an inverted omega ((J). Therefore we may also descdbe an 8 O resistor as having a conductance of 0.125 nho, ((')....
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