Editing Series and parallel circuits (section)

==Applications==
A common application of series circuit in consumer electronics is in batteries, where several cells connected in series are used to obtain a convenient operating voltage. Two disposable zinc cells in series might power a flashlight or remote control at 3 volts; the battery pack for a hand-held power tool might contain a dozen lithium-ion cells wired in series to provide 48 volts.

Series circuits were formerly used for lighting in [[electric multiple units]] trains.  For example, if the supply voltage was 600 volts there might be eight 70-volt bulbs in series (total 560 volts) plus a [[resistor]] to drop the remaining 40 volts.  Series circuits for train lighting were superseded, first by [[motor-generator]]s, then by [[Solid state (electronics)|solid state]] devices.

Series resistance can also be applied to the arrangement of blood vessels within a given organ.  Each organ is supplied by a large artery, smaller arteries, arterioles, capillaries, and veins arranged in series. The total resistance is the sum of the individual resistances, as expressed by the following equation: {{math|1=''R''<sub>total</sub> = ''R''<sub>artery</sub> + ''R''<sub>arterioles</sub> + ''R''<sub>capillaries</sub>}}. The largest proportion of resistance in this series is contributed by the arterioles.<ref name="BRS"/>

Parallel resistance is illustrated by the [[circulatory system]]. Each organ is supplied by an artery that branches off the [[aorta]]. The total resistance of this parallel arrangement is expressed by the following equation: {{math|1=1/''R''<sub>total</sub> = 1/''R''<sub>a</sub> + 1/''R''<sub>b</sub> + ... + 1/''R''<sub>n</sub>}}. {{math|''R''<sub>a</sub>}}, {{math|''R''<sub>b</sub>}}, and {{math|''R''<sub>n</sub>}} are the resistances of the renal, hepatic, and other arteries respectively. The total resistance is less than the resistance of any of the individual arteries.<ref name="BRS"/>