# Resistors in Series and in Parallel

• Ordinary circuits contain many elements; it often simplifies analysis to reduce the circuit to a simpler state with fewer elements.
• Connecting elements in series forces all current to pass through each element.
• Connecting elements in parallel permits current to pass through only one element.
• Several resistors connected in series have equivalent resistance
```            R(eq) = R1 + R2 + R3 +  ....             (in series)
```
The equivalent resistance is larger than each individual resistance.
• Several resistors connected in parallel have equivalent resistance
```              1      1     1     1
----    --- + --- + --- + ...            (in parallel)
R(eq) =  R1    R2    R3
```
The equivalent resistance is smaller than each individual resistance.
• We can use these rules to build resistances of almost any value we need from just a few different types of resistors.

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