Series and parallel circuits: Difference between revisions

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[[File:Series circuit.svg|thumb|A series circuit with a [[voltage source]] (such as a battery, or in this case a cell) and three resistance units]]

[[Terminal (electronics)|Two-terminal]] components and [[electrical networks]] can be connected in '''series''' or '''parallel'''. The resulting electrical network will have two terminals, and itself can participate in a series or parallel [[Topology (electrical circuits)|topology]]. Whether a two-terminal "object" is an electrical component (e.g. a [[resistor]]) or an electrical network (e.g. resistors in series) is a matter of perspective. This article will use "component" to refer to a two-terminal "object" that participateparticipates in the series/parallel networks.

Components connected in series are connected along a single "electrical path", and each component has the same [[electric current|current]] through it, equal to the current through the network. The voltage across the network is equal to the sum of the voltages across each component.<ref name="Resnick_1966"/><ref name="Smith_1966"/>

Components connected in parallel are connected along multiple paths, and each component has the same [[voltage]] across it, equal to the voltage across the network. The current through the network is equal to the sum of the currents through each component.

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A circuit composed solely of components connected in series is known as a '''series circuit'''; likewise, one connected completely in parallel is known as a '''parallel circuit'''. Many circuits can be analyzed as a combination of series and parallel circuits, along with [[Topology (electrical circuits)|other configurations]].

In a series circuit, the current that flows through each of the components is the same, and the [[voltage]] across the circuit is the sum of the individual [[voltage drop]]s across each component.<ref name="Resnick_1966"/> In a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents flowing through each component.<ref name="Resnick_1966"/>

Consider a very simple circuit consisting of four light bulbs and a 12-volt [[automotive battery]]. If a wire joins the battery to one bulb, to the next bulb, to the next bulb, to the next bulb, then back to the battery in one continuous loop, the bulbs are said to be in series. If each bulb is wired to the battery in a separate loop, the bulbs are said to be in parallel. If the four light bulbs are connected in series, the same current flows through all of them and the voltage drop is 3 volts across each bulb, which may not be sufficient to make them glow. If the light bulbs are connected in parallel, the currents through the light bulbs combine to form the current in the battery, while the voltage drop is 12 volts across each bulb and they all glow.

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{{Electromagnetism|Network}}

'''Series circuits''' are sometimes referred to as current-coupled or [[Daisy chain (electrical engineering)|daisy chain]]-coupled. The [[electric current]] in a series circuit goes through every component in the circuit. Therefore, all of the components in a series connection carry the same current.

A series circuit has only one path through which its current can flow. Opening or breaking a series circuit at any [[Single point of failure|point]] causes the entire circuit to "open" or stop operating. For example, if even one of the light bulbs in an older-style string of [[Christmas tree lights]] burns out or is removed, the entire string becomes inoperable until the faulty bulb is replaced.

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===Voltage===

In a series circuit, the voltage is the sum of the voltage drops of the individual components (resistance units).

<math display="block">V = V_1 + V_2 + \dotssum_{i=1}^n + V_nV_i = I \left(sum_{i=1}^n R_1 + R_2 + \dots + R_n \right)R_i</math>

===Resistance units<span class="anchor" id="Rseries"></span>===

The total resistance of two or more resistors connected in series is equal to the sum of their individual resistances:

[[File:Resistors in seriesResistors_in_series.svg|alt=This is a diagram of several resistors, connected end to end, with the same amount of current through each.|border|center|x100px]]

<math display="block">R_\text{total}R = R_\textsum_{si=1}^n R_i = R_1 + R_2 + R_3 \cdots + R_n.</math>

[[File:Resistors in series.svg|This is a diagram of several resistors, connected end to end, with the same amount of current through each.]]

<math display="block">R_\text{total} = R_\text{s} = R_1 + R_2 + \cdots + R_n.</math>

{{anchor|Lseries}}

Here, the subscript ''s'' in {{math|''R''_s}} denotes "series", and {{math|''R''_s}} denotes resistance in a series.

==== Conductance ====

[[Electrical conductance]] presents a reciprocal quantity to resistance. Total conductance of a series circuits of pure resistances, therefore, can be calculated from the following expression:

<math display="block">G = \fracleft(\sum_{i=1}^n{G_1\text{totalover G_i}\right)^{-1} = \fracleft({1}{\over G_1} + \frac{1}{\over G_2} + {1\cdotsover G_3} + \fracdots + {1\over G_n}\right)^{G_n-1}.</math>

For a special case of two conductances in series, the total conductance is equal to:

<math display="block">G_\text{total}G = \frac{G_1 G_2}{G_1 + G_2}.</math>

===Inductors <span class="anchor" id="Lseries"></span>===

[[Inductor]]s follow the same law, in that the total [[inductance]] of non-coupled inductors in series is equal to the sum of their individual inductances:

[[File:Inductors in series.svg|A diagram of several inductors, connected end to end, with the same amount of current going through each.|border|center|x100px]]

<math display="block">L_L = \mathrmsum_{totali=1}^n L_i = L_1 + L_2 + L_3 \cdots + L_n.</math>

However, in some situations, it is difficult to prevent adjacent inductors from influencing each other as the magnetic field of one device couples with the windings of its neighbors. This influence is defined by the mutual inductance M. For example, if two inductors are in series, there are two possible equivalent inductances depending on how the magnetic fields of both inductors influence each other.

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Therefore

<math display="block">L_\text{total}L = \left(M_{11} + M_{22} + M_{33}\right) + \left(M_{12} + M_{13} + M_{23}\right) + \left(M_{21} + M_{31} + M_{32}\right)</math>

By reciprocity, <math>M_{ij}</math> = <math>M_{ji}</math> so that the last two groups can be combined. The first three terms represent the sum of the self-inductances of the various coils. The formula is easily extended to any number of series coils with mutual coupling. The method can be used to find the self-inductance of large coils of wire of any cross-sectional shape by computing the sum of the mutual inductance of each turn of wire in the coil with every other turn since in such a coil all turns are in series.

===Capacitors<span class="anchor" id="Cseries"></span>===

{{seeSee also|Capacitor#Networks}}

[[Capacitor]]s follow the same law using the reciprocals. The total [[capacitance]] of capacitors in series is equal to the reciprocal of the sum of the [[Multiplicative inverse|reciprocals]] of their individual capacitances:

[[File:Capacitors in seriesCapacitors_in_series.svg|alt=A diagram of several capacitors, connected end to end, with the same amount of current going through each.|border|center|x100px]]

<math display="block">C = \fracleft(\sum_{i=1}^n{C_1\text{totalover C_i}\right)^{-1} = \fracleft({1}{\over C_1} + \frac{1}{\over C_2} + {1\cdotsover C_3} + \fracdots + {1\over C_n}\right)^{C_n-1}.</math>

[[File:Capacitors in series.svg|A diagram of several capacitors, connected end to end, with the same amount of current going through each.]]

<math display="block">\frac{1}{C_\text{total}} = \frac{1}{C_1} + \frac{1}{C_2} + \cdots + \frac{1}{C_n}.</math>

Equivalently using [[elastance]] (the reciprocal of capacitance), the total series elastance equals the sum of each capacitor's elastance.

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===Cells and batteries===

A [[Battery (electricity)|battery]] is a collection of [[electrochemical cell]]s. If the cells are connected in series, the [[voltage]] of the battery will be the sum of the cell voltages. For example, a 12 volt [[car battery]] contains six 2-volt cells connected in series. Some vehicles, such as trucks, have two 12 volt batteries in series to feed the 24-volt system.

==Parallel circuits<span class="anchor" id="Zparallel"></span><span class="anchor" id="Xparallel"></span><span class="anchor" id="Yparallel"></span><span class="anchor" id="Bparallel"></span><span class="anchor" id="Parallel_circuit_anchor"></span>Parallel circuits==

<!-- "Parallel circuit" redirects here. -->

{{resistors inductors capacitors in series and parallel.svg}}

If two or more components are connected in parallel, they have the same difference of potential ([[voltage]]) across their ends. The potential differences across the components are the same in magnitude, and they also have identical polarities. The same voltage is applied to all circuit components connected in parallel. The total current is the sum of the currents through the individual components, in accordance with [[Kirchhoff's circuit laws#Kirchhoff's current law (KCL)|Kirchhoff's current law]].

===Voltage<span class="anchor" id="Rparallel"></span>===

In a '''parallel circuit''', the voltage is the same for all elements.

<math display="block">V = V_1 = V_2 = \dots = V_n</math>

===Current===

The current in each individual resistor is found by [[Ohm's law]]. Factoring out the voltage gives

<math display="block">I_\text{total}I = I_1 + I_2 + \cdotssum_{i=1}^n + I_nI_i = V\left(\fracsum_{i=1}{R_1} + \frac^n{1}{R_2} + \cdotsover + \frac{1R_i}{R_n}\right).</math>

===Resistance units===

To find the total [[Electrical resistance|resistance]] of all components, add the [[multiplicativeMultiplicative inverse|reciprocals]] of the resistances <math>R_i</math> of each component and take the reciprocal of the sum. Total resistance will always be less than the value of the smallest resistance:

[[File:Resistors in parallelResistors_in_parallel.svg|alt=A diagram of several resistors, side by side, both leads of each connected to the same wires.|border|center|x120px]]

<math display="block">R = \fracleft(\sum_{i=1}^n{R_1\text{totalover R_i}\right)^{-1} = \fracleft({1}{\over R_1} + \frac{1}{\over R_2} + {1\cdotsover R_3} + \fracdots + {1\over R_n}\right)^{R_n-1}.</math>

[[File:Resistors in parallel.svg|A diagram of several resistors, side by side, both leads of each connected to the same wires.]]

<math display="block">\frac{1}{R_\text{total}} = \frac{1}{R_1} + \frac{1}{R_2} + \cdots + \frac{1}{R_n}.</math>

For only two resistances, the unreciprocated expression is reasonably simple:

<math display="block">R_\text{total}R = \frac{R_1 R_2}{R_1 + R_2} .</math>

This sometimes goes by the mnemonic ''product over sum''.

For ''N'' equal resistances in parallel, the reciprocal sum expression simplifies to:

<math display="block">\frac{1}{R_\text{total}R} = N \frac{1}{R}.</math>

and therefore to:

<math display="block">R_\text{total}R = \frac{R}{N}.</math>

To find the [[current (electricity)|current]] in a component with resistance <math>R_i</math>, use Ohm's law again:

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An old term for devices connected in parallel is ''multiple'', such as multiple connections for [[arc lamp]]s.

==== Conductance ====

Since electrical conductance <math>G</math> is reciprocal to resistance, the expression for total conductance of a parallel circuit of resistors readsis simply:

<math display="block">G_G = \textsum_{totali=1}^n G_i = G_1 + G_2 + G_3 \cdots + G_n.</math>

The relations for total conductance and resistance stand in a complementary relationship: the expression for a series connection of resistances is the same as for parallel connection of conductances, and vice versa.

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===Inductors<span class="anchor" id="Lparallel"></span>===

[[Inductor]]s follow the same law, in that the total [[inductance]] of non-coupled inductors in parallel is equal to the reciprocal of the sum of the reciprocals of their individual inductances:

[[File:Inductors in parallelInductors_in_parallel.svg|alt=A diagram of several inductors, side by side, both leads of each connected to the same wires.|border|center|x120px]]

<math display="block">L = \fracleft(\sum_{i=1}^n{L_1\text{totalover L_i}\right)^{-1} = \fracleft({1}{\over L_1} + \frac{1}{\over L_2} + {1\cdotsover L_3} + \fracdots + {1\over L_n}\right)^{L_n-1}.</math>

[[File:Inductors in parallel.svg|A diagram of several inductors, side by side, both leads of each connected to the same wires.]]

<math display="block">\frac{1}{L_\text{total}} = \frac{1}{L_1} + \frac{1}{L_2} + \cdots + \frac{1}{L_n}.</math>

If the inductors are situated in each other's magnetic fields, this approach is invalid due to mutual inductance. If the mutual inductance between two coils in parallel is {{mvar|M}}, the equivalent inductor is:

<math display="block">\frac{1}{L_\text{total}}L = \frac{L_1L_2 - M^2}{L_1 + L_2 - 2M}{L_1L_2 - M^2}</math>

If <math>L_1 = L_2</math>

<math display="block"> L_\text{total}L = \frac{L + M}{2}</math>

The sign of <math>M</math> depends on how the magnetic fields influence each other. For two equal tightly coupled coils the total inductance is close to that of every single coil. If the polarity of one coil is reversed so that {{mvar|M}} is negative, then the parallel inductance is nearly zero or the combination is almost non-inductive. It is assumed in the "tightly coupled" case {{mvar|M}} is very nearly equal to {{mvar|L}}. However, if the inductances are not equal and the coils are tightly coupled there can be near short circuit conditions and high circulating currents for both positive and negative values of {{mvar|M}}, which can cause problems.

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===Capacitors<span class="anchor" id="Cparallel"></span>===

The total [[capacitance]] of [[capacitors]] in parallel is equal to the sum of their individual capacitances:

[[File:Capacitors in parallelCapacitors_in_parallel.svg|alt=A diagram of several capacitors, side by side, both leads of each connected to the same wires.|border|center|x120px]]

<math display="block">C_C = \textsum_{totali=1}^n C_i = C_1 + C_2 + C_3 \cdots + C_n.</math>

[[File:Capacitors in parallel.svg|A diagram of several capacitors, side by side, both leads of each connected to the same wires.]]

<math display="block">C_\text{total} = C_1 + C_2 + \cdots + C_n.</math>

The working voltage of a parallel combination of capacitors is always limited by the smallest working voltage of an individual capacitor.

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==Combining conductances<span class="anchor" id="Gparallel"></span><span class="anchor" id="Gseries"></span>==

From [[Kirchhoff's circuit laws]] the rules for combining conductance can be deducted. For two conductances <math>G_1</math> and <math>G_2</math> in ''parallel'', the voltage across them is the same and from Kirchhoff's current law (KCL) the total current is

<math display="block">I_\text{eq}I = I_1 + I_2.</math>

Substituting Ohm's law for conductances gives

<math display="block">G_\text{eq}G V = G_1 V + G_2 V</math>

and the equivalent conductance will be,

<math display="block">G_\text{eq}G = G_1 + G_2.</math>

For two conductances <math>G_1</math> and <math>G_2</math> in '''series''' the current through them will be the same and Kirchhoff's Voltage Law says that the voltage across them is the sum of the voltages across each conductance, that is,

<math display="block">V_\text{eq}V = V_1 + V_2.</math>

Substituting Ohm's law for conductance then gives,

<math display="block">\frac{I}{G_\text{eq}G} = \frac{I}{G_1} + \frac{I}{G_2}</math>

which in turn gives the formula for the equivalent conductance,

<math display="block">\frac{1}{G_\text{eq}G} = \frac{1}{G_1} + \frac{1}{G_2}.</math>

This equation can be rearranged slightly, though this is a special case that will only rearrange like this for two components.

<math display="block">G_\text{eq}G = \frac{G_1 G_2}{G_1 + G_2}.</math>

For three conductances in series,

<math display="block">G_\text{eq}G = \frac{G_1 G_2 G_3}{G_1 G_2 + G_1 G_3 + G_2 G_3}.</math>

==Notation==

The value of two components in parallel is often represented in equations by the [[parallel (operator)|parallel operator]], two vertical lines (∥), borrowing the [[Parallel (geometry)#Symbol|parallel lines notation from geometry]].

<math display="block">R_\mathrm{eq}R \equiv R_1 \parallel R_2 \equiv \left(R_1^{-1} + R_2^{-1}\right)^{-1} \equiv \frac{R_1 R_2}{R_1 + R_2}</math>

This simplifies expressions that would otherwise become complicated by expansion of the terms. For instance:

<math display="block">R_1 \parallel R_2 \parallel R_3 \equiv \frac{R_1 R_2 R_3}{R_1 R_2 + R_1 R_3 + R_2 R_3} . </math>

If {{math|''n''}} components are in parallel, then

<math display="block">R_\text{eq} = \left(\sum_i^n {R_i}^{-1}\right)^{-1}</math>

==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-generatormotor–generator]]s, then by [[Solid 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''_total = ''R''_artery + ''R''_arterioles + ''R''_capillaries}}. The largest proportion of resistance in this series is contributed by the arterioles.<ref name="BRS"/>

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==See also==

{{div col}}

* [[Anti-parallel (electronics)]]

* [[Electrical impedance#Combining impedances|Combining impedances]]

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* [[Wheatstone bridge]]

* [[Y-Δ transform]]

{{div col end}}

==References==

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<ref name="Smith_1966">{{cite book |author-last=Smith |author-first=R. J. |date=1966 |title=Circuits, Devices and Systems |publisher=[[Wiley (publisher)|Wiley]] |edition=International |___location=New York |lccn=66-17612 |page=21 }}</ref>

<ref name="BRS">{{cite book |series=Board Review Series |title=Physiology |author-first=Linda S. |author-last=Costanzo |page=74 }}</ref>

<ref name="Ellerman_1995">{{cite book |title=Intellectual Trespassing as a Way of Life: Essays in Philosophy, Economics, and Mathematics |chapter=Chapter 12: Parallel Addition, Series-Parallel Duality, and Financial Mathematics |series=G - Reference, Information and Interdisciplinary Subjects Series |work=The worldly philosophy: studies in intersection of philosophy and economics |author-first=David Patterson |author-last=Ellerman |author-link=David Patterson Ellerman |edition=illustrated |publisher=[[Rowman & Littlefield Publishers, Inc.]] |date=1995-03-21 |isbn=0-8476-7932-2 |pages=237–268 |url=http://www.ellerman.org/wp-content/uploads/2012/12/IntellectualTrespassingBook.pdf |chapter-url=https://books.google.com/books?id=NgJqXXk7zAAC&pg=PA237 |access-date=2019-08-09 |url-status=live |archive-url=https://web.archive.org/web/20160305012729/http://www.ellerman.org/wp-content/uploads/2012/12/IntellectualTrespassingBook.pdf |archive-date=2016-03-05 |quote=[…] When resistors with resistance a and b are placed in series, their compound resistance is the usual sum (hereafter the ''[[series sum]]'') of the resistances a&nbsp;+ b. If the resistances are placed in parallel, their compound resistance is the ''[[parallel sum]]'' of the resistances, which is denoted by the [[full colon]] […]}} [https://web.archive.org/web/20150917191423/http://www.ellerman.org/Davids-Stuff/Maths/sp_math.doc] (271 pages)</ref>

<ref name="Ellerman_2004">{{cite web |title=Introduction to Series-Parallel Duality |author-first=David Patterson |author-last=Ellerman |author-link=David Patterson Ellerman |publisher=[[University of California at Riverside]] |date=May 2004 |orig-year=1995-03-21 |citeseerx=10.1.1.90.3666 |url=http://www.ellerman.org/wp-content/uploads/2012/12/Series-Parallel-Duality.CV_.pdf |access-date=2019-08-09 |url-status=live |archive-url=https://web.archive.org/web/20190810011716/http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.90.3666&rep=rep1&type=pdf<!-- https://archive.today/20190810080659/http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.90.3666&rep=rep1&type=pdf --> |archive-date=2019-08-10 |quote=The [[parallel sum]] of two positive real numbers x:y&nbsp;= [(1/x)&nbsp;+ (1/y)]⁻¹ arises in electrical circuit theory as the resistance resulting from hooking two resistances x and y in parallel. There is a [[duality (mathematics)|duality]] between the usual [[series sum|(series) sum]] and the parallel sum. […]}} [http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.90.3666&rep=rep1&type=pdf] (24 pages)</ref>

}}

==Further reading==

* {{cite book |author-last=Williams |author-first=Tim |title=The Circuit Designer's Companion |publisher=[[Butterworth-Heinemann]] |date=2005 |isbn=0-7506-6370-7 }}

* {{cite magazine |url=http://www.edn.com/design/components-and-packaging/4421194/Resistor-combinations--How-many-values-using-1kohm-resistors-- |title=Resistor combinations: How many values using 1K ohm resistors? |magazine=[[EDN magazine]] }}

* {{cite book |chapter-url=https://www.grund-wissen.de/physik/mechanik/festkoerper-fluessigkeiten-gase/fluessigkeiten.html |title=Mechanik der Flüssigkeiten |chapter=Strömungswiderstand |language=de |date=2018-01-04 |author-first=Bernhard |author-last=Grotz }}<!-- analog parallel and serial circuits. Find English source and add to article -->

[[Category:Electrical circuits]]