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Resistors in Series

Suppose in a section of a circuit we encounter a combination of two resistors as in Fig. 17.4:
  
Figure 17.4: Two resistors in series
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These resistors are said to be in series, and as indicated, it is possible to consider them as one single equivalent resistor R eq . To find this equivalent resistor, we exploit the fact from energy conservation that Vac = Vab + Vbc , which using Ohm's law (17.3) becomes

 
IR eq = IR1 + IR2 $\displaystyle\rightarrow$ R eq = R1 + R2. (7)

This is readily extended to the case of multiple resistors R1,R2,...,RN in series:

Req = R1 + R2 +...+ RN. (8)


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10/9/1997