specify the term equivalent resistance calculation the tantamount resistance of resistors associated in collection Calculate the tantamount resistance the resistors associated in parallel

In Current and also Resistance, we explained the term ‘resistance’ and explained the simple design of a resistor. Basically, a resistor limits the circulation of fee in a circuit and is an ohmic maker where (V = IR). Many circuits have an ext than one resistor. If numerous resistors are connected together and also connected come a battery, the present supplied by the battery depends on the equivalent resistance of the circuit.

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The indistinguishable resistance that a mix of resistors counts on both their individual values and how they space connected. The simplest combinations of resistors are series and parallel relations (Figure (PageIndex1)). In a series circuit, the output current of the an initial resistor flows into the input of the second resistor; therefore, the present is the same in each resistor. In a parallel circuit, every one of the resistor leader on one side of the resistors are associated together and also all the leader on the various other side are associated together. In the situation of a parallel configuration, every resistor has the very same potential drop across it, and also the currents with each resistor might be different, relying on the resistor. The sum of the separation, personal, instance currents amounts to the existing that flows into the parallel connections.

Figure (PageIndex1): (a) for a collection connection of resistors, the present is the exact same in every resistor. (b) because that a parallel link of resistors, the voltage is the same across each resistor.

Resistors in Series

Resistors are stated to be in series whenever the existing flows v the resistors sequentially. Consider Figure (PageIndex2), which shows three resistors in series with an used voltage equal to (V_ab). Because there is just one path for the dues to circulation through, the present is the very same through each resistor. The identical resistance of a set of resistors in a series connection is equal to the algebraic sum of the individual resistances.

Figure (PageIndex2): (a) three resistors connected in collection to a voltage source. (b) The original circuit is diminished to an tantamount resistance and a voltage source.

In number (PageIndex2), the existing coming indigenous the voltage source flows v each resistor, so the present through each resistor is the same. The current through the circuit depends on the voltage offered by the voltage source and the resistance that the resistors. Because that each resistor, a potential drop occurs that is same to the lose of electrical potential energy as a current travels with each resistor. According to Ohm’s law, the potential fall (V) throughout a resistor as soon as a current flows with it is calculated using the equation (V = IR), wherein (I) is the existing in amps ((A)) and also (R) is the resistance in ohms ((Omega)). Because energy is conserved, and the voltage is equal to the potential energy per charge, the sum of the voltage applied to the circuit by the resource and the potential drops throughout the separation, personal, instance resistors approximately a loop have to be same to zero:

This equation is often referred to as Kirchhoff’s loop law, which we will look in ~ in an ext detail later in this chapter. For number (PageIndex2), the sum of the potential autumn of each resistor and the voltage gave by the voltage resource should equal zero:

<eginalign* V - V_1 - V_2 - V_3 &= 0, \<4pt>V &= V_1 + V_2 + V_3, \<4pt> &= IR_1 + IR_2 + IR_3, endalign*>

Solving because that (I)

<eginalign* i &= fracVR_1 + R_2 + R_3 \<4pt> &= fracVR_S. endalign*>

Since the current through each component is the same, the equality can be streamlined to an indistinguishable resistance ((R_S)), i beg your pardon is simply the sum of the resistances the the individual resistors.

One an outcome of components associated in a series circuit is the if something wake up to one component, it affects all the various other components. Because that example, if number of lamps are associated in collection and one bulb burns out, all the various other lamps go dark.

Example (PageIndex1): equivalent Resistance, Current, and Power in a series Circuit

A battery through a terminal voltage the 9 V is associated to a circuit consists of four (20 , Omega) and one (10 , Omega) resistors all in series (Figure (PageIndex3)). I think the battery has negligible interior resistance.

calculation the identical resistance that the circuit. Calculation the existing through each resistor. Calculate the potential drop across each resistor. Recognize the total power dissipated by the resistors and also the power offered by the battery.
api/deki/files/8225/CNX_Ukeolistravelservices.comics_27_01_ResPara.jpg?revision=1" />Figure (PageIndex4): Two resistors linked in parallel come a voltage source. (b) The initial circuit is reduced to an identical resistance and a voltage source.

The existing flowing from the voltage resource in number (PageIndex4) relies on the voltage supplied by the voltage resource and the equivalent resistance of the circuit. In this case, the current flows native the voltage source and start a junction, or node, whereby the circuit splits flowing through resistors (R_1) and also (R_2). As the charges flow from the battery, some go through resistor (R_1) and also some circulation through resistor (R_2). The amount of the currents flowing into a junction need to be equal to the sum of the currents flowing out of the junction:

This equation is referred to as Kirchhoff’s junction rule and also will be disputed in detail in the next section. In figure (PageIndex4), the junction ascendancy gives (I = I_1 + I_2). There room two loops in this circuit, which leads to the equations (V = I_1R_1) and (I_1R_1 = I_2R_2). Keep in mind the voltage across the resistors in parallel are the same ( (V = V_1 = V_2)) and the present is additive:

< eginalign* i &= I_1 + I_2 \<4pt> &= fracV_1R_1 + fracV_2R_2 \<4pt> &= fracVR_1 + fracVR_2\<4pt> &= V left( frac1R_1 + frac1R_2 ight) = fracVR_Pendalign*>

Solving for the (R_P)

This connection results in an equivalent resistance (R_P) that is less than the the smallest of the individual resistances. Once resistors are linked in parallel, more current operation from the source than would circulation for any kind of of castle individually, for this reason the total resistance is lower.

Example (PageIndex2): analysis of a parallel circuit

Three resistors (R_1 = 1.00 , Omega), (R_2 = 2.00 , Omega), and also (R_3 = 2.00 , Omega), are associated in parallel. The parallel connection is attached to a (V = 3.00 , V) voltage source.

What is the identical resistance? uncover the existing supplied by the source to the parallel circuit. Calculate the currents in each resistor and also show the these add together to equal the present output that the source. Calculation the power dissipated by each resistor. Find the strength output of the resource and present that it amounts to the complete power dissipated by the resistors.


(a) The full resistance because that a parallel combination of resistors is discovered using Equation ef10.3.(Note the in this calculations, each intermediate prize is presented with an extra digit.)

(b) The current supplied by the source can be uncovered from Ohm’s law, substituting (R_P) for the complete resistance (I = fracVR_P).

(c) The individual currents are conveniently calculated indigenous Ohm’s regulation (left(I_i = fracV_iR_i ight)), since each resistor it s okay the complete voltage. The total current is the amount of the individual currents:

(d) The power dissipated by every resistor deserve to be uncovered using any of the equations relating strength to current, voltage, and also resistance, due to the fact that all three room known. Let us use (P_i = V^2 /R_i), since each resistor gets complete voltage.

(e) The total power can likewise be calculated in several ways, usage (P = IV).


The full resistance for a parallel combination of resistors is uncovered using Equation ef10.3. Entering known values provides The total resistance with the exactly number of far-ranging digits is (R_eq = 0.50 , Omega). Together predicted, (R_P) is much less than the smallest individual resistance. The total current have the right to be uncovered from Ohm’s law, substituting (R_P) for the total resistance. This provides present I for each device is much larger than for the very same devices connected in series (see the vault example). A circuit through parallel connections has actually a smaller full resistance 보다 the resistors connected in series. The separation, personal, instance currents are easily calculated indigenous Ohm’s law, since each resistor gets the complete voltage. Thus, Similarly, and The full current is the amount of the separation, personal, instance currents: The strength dissipated by each resistor have the right to be uncovered using any of the equations relating power to current, voltage, and resistance, because all three space known. Let united state use (P = V^2 /R), because each resistor gets full voltage. Thus, Similarly, and The total power can additionally be calculate in numerous ways. Choosing (P = IV) and also entering the full current yields


Total power dissipated through the resistors is likewise 18.00 W:

Notice the the total power dissipated through the resistors equals the power provided by the source.

Exercise (PageIndex2A)

Consider the very same potential difference ((V = 3.00 , V)) applied to the exact same three resistors associated in series. Would certainly the identical resistance of the series circuit be higher, lower, or equal to the 3 resistor in parallel? would the existing through the series circuit it is in higher, lower, or same to the current listed by the exact same voltage applied to the parallel circuit? exactly how would the power dissipated through the resistor in series compare to the strength dissipated through the resistors in parallel?


The tantamount of the series circuit would certainly be (R_eq = 1.00 , Omega + 2.00 , Omega + 2.00 , Omega = 5.00 , Omega), which is higher than the equivalent resistance that the parallel circuit (R_eq = 0.50 , Omega). The indistinguishable resistor the any number of resistors is always higher than the identical resistance that the very same resistors linked in parallel. The existing through because that the series circuit would certainly be (I = frac3.00 , V5.00 , Omega = 0.60 , A), which is reduced than the sum of the currents through each resistor in the parallel circuit, (I = 6.00 , A). This is not surprising due to the fact that the tantamount resistance the the collection circuit is higher. The present through a collection connection that any number of resistors will constantly be reduced than the present into a parallel connection of the exact same resistors, since the indistinguishable resistance that the collection circuit will be higher than the parallel circuit. The strength dissipated by the resistors in collection would it is in (P = 1.800 , W), i m sorry is lower than the strength dissipated in the parallel circuit (P = 18.00 , W).

Let united state summarize the significant features of resistors in parallel:

indistinguishable resistance is found from Equation ef10.3and is smaller sized than any individual resistance in the combination. The potential drop across each resistor in parallel is the same. Parallel resistors do not each obtain the full current; they divide it. The present entering a parallel mix of resistors is same to the amount of the existing through each resistor in parallel.

In this chapter, we presented the tantamount resistance the resistors connect in series and resistors connected in parallel. You may recall indigenous the ar onCapacitance, we presented the equivalent capacitance that capacitors connected in series and parallel. Circuits often contain both capacitors and also resistors. Table (PageIndex1) summarizes the equations used for the equivalent resistance and also equivalent capacitance for series and parallel connections.

Table (PageIndex1): an overview for identical Resistance and Capacitance in series and Parallel combine Series combination Parallel combination
Equivalent capacitance
Equivalent resistance

Combinations of series and Parallel

More complicated connections that resistors are regularly just combinations of series and parallel connections. Together combinations are common, specifically when cable resistance is considered. In the case, cable resistance is in collection with other resistances that space in parallel.

Combinations of series and parallel can be decreased to a solitary equivalent resistance using the an approach illustrated in figure (PageIndex5). Miscellaneous parts can be determined as either collection or parallel connections, lessened to their tantamount resistances, and also then further lessened until a single equivalent resistance is left. The procedure is more time consuming than difficult. Here, we note the tantamount resistance together (R_eq).

Figure (PageIndex5): (a) The initial circuit of four resistors. (b) action 1: The resistors (R_3) and also (R_4) space in series and the identical resistance is (R_34 = 10 , Omega) (c) action 2: The diminished circuit mirrors resistors (R_2) and also (R_34) room in parallel, with an equivalent resistance the (R_234 = 5 , Omega). (d) step 3: The reduced circuit mirrors that (R_1) and also (R_234) room in collection with an indistinguishable resistance of (R_1234 = 12 , Omega) i beg your pardon is the equivalent resistance (R_eq). (e) The decreased circuit through a voltage source of (V = 24 , V) with an identical resistance the (R_eq = 12 , Omega). This outcomes in a present of (I = 2 , A) indigenous the voltage source.

Notice that resistors (R_3) and also (R_4) are in series. They deserve to be merged into a single equivalent resistance. One method of maintaining track of the process is to encompass the resistors together subscripts. Right here the indistinguishable resistance that (R_3) and also (R_4) is

The circuit currently reduces to 3 resistors, presented in number (PageIndex5c). Redrawing, we currently see that resistors (R_2) and also (R_34) constitute a parallel circuit. Those 2 resistors can be decreased to an equivalent resistance:

This action of the process reduces the circuit to two resistors, displayed in in figure (PageIndex5d). Here, the circuit reduce to two resistors, i m sorry in this case are in series. These 2 resistors have the right to be reduced to an equivalent resistance, i m sorry is the tantamount resistance the the circuit:

The key goal of this circuit evaluation is reached, and the circuit is now diminished to a single resistor and solitary voltage source.

Now we have the right to analyze the circuit. The current provided by the voltage source is (I = fracVR_eq = frac24 , V12 , Omega = 2 , A). This current runs with resistor (R_1) and also is designated as (I_1). The potential drop across (R_1) can be discovered using Ohm’s law:

Looking at number (PageIndex5c), this pipeline (24 , V - 14 , V = 10 , V) to be dropped across the parallel mix of (R_2) and also (R_34). The present through (R_2) deserve to be uncovered using Ohm’s law:

The resistors (R_3) and (R_4) space in collection so the currents (I_3) and (I_4) are equal to

Using Ohm’s law, us can find the potential drop throughout the last two resistors. The potential drops room (V_3 = I_3R_3 = 6 , V) and also (V_4 = I_4R_4 = 4 , V). The final analysis is come look in ~ the power provided by the voltage source and the power dissipated by the resistors. The power dissipated through the resistors is

<eginalign*P_1 &= I_1^2R_1 = (2 , A)^2 (7 , Omega) = 28 , W, \<4pt>P_2&= I_2^2R_2 = (1 , A)^2 (10 , Omega) = 10 , W,\<4pt>P_3 &= I_3^2R_3 = (1 , A)^2 (6 , Omega) = 6 , W,\<4pt>P_4 &= I_4^2R_4 = (1 , A)^2 (4 , Omega) = 4 , W,\<4pt>P_dissipated &= P_1 + P_2 + P_3 + P_4 = 48 , W. endalign*>

The total energy is consistent in any kind of process. Therefore, the power offered by the voltage source is

<eginalign* P_s&= IV \<4pt> &= (2 , A)(24 , V) = 48 , W endalign*>

Analyzing the power supplied to the circuit and also the strength dissipated by the resistors is a great check for the validity of the analysis; they have to be equal.

Example (PageIndex3): Combining series and parallel circuits

Figure (PageIndex6) shows resistors wired in a mix of collection and parallel. We can take into consideration (R_1) to it is in the resistance the wires causing (R_2) and also (R_3).

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uncover the identical resistance the the circuit. What is the potential fall (V_1) across resistor (R_1)? find the current (I_2) through resistor (R_2). What power is dissipated by (R_2)?

Example (PageIndex4): Combining collection and Parallel circuits

Two resistors connected in series ((R_1, , R_2)) are associated to two resistors the are associated in parallel ((R_3, , R_4)). The series-parallel combination is connected to a battery. Each resistor has actually a resistance the 10.00 Ohms. The wires connecting the resistors and also battery have negligible resistance. A present of 2.00 Amps runs through resistor (R_1). What is the voltage supplied by the voltage source?


Use the procedures in the coming before problem-solving strategy to discover the solution for this example.