Resistors In Parallel Formula: Definition And Features

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Jasmine Grover

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Resistors can be termed as the universal components in the electronic industry. In circuits analysis, the values of two or more resistors are required known, hence we use resistors in the parallel formula.

Key Terms: Electric, Circuit, Resistance, Formula, Network, Current, Reciprocal, Components, Resistor, complex network


What Is Resistors In The Parallel?

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Resistors are either connected as a series or in a parallel pattern when both of their terminals are respectively connected to each terminal of the other resistor or resistors to create a more complex network. 

Resistors In Parallel

Resistors In Parallel

The voltage across the resistors for each resistor in a parallel pattern will be the same whereas the current will be in proportion to the resistance of each individual resistor. When resistors are connected in parallel, then the supply current is equal to the sum of the currents through each resistor.

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Formula Of Resistors In Parallel

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To find the equivalent resistance of a number of resistors in parallel, the reciprocal of resistance i.e. 1/R is used. The reciprocal of the equivalent resistance is equal to the sum of the reciprocals of each resistance.

\(\frac{1}{R_{Total}} =\frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}.......\frac{1}{R_n}\)

The unit of resistance is the Ohm, which is equal to a Volt per Ampere. Larger resistors with kilo-Ohm or mega-Ohm resistances are common, as well.

RTotal = R1 + R2 + R3………. + Rn

Resistors In Series


Features Of Resistors In Parallel

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The major features of the resistors in parallel are: 

  • Parallel resistance is smaller than any individual resistance in the combination.
  • Each parallel resistor has an equal amount of voltage of the source which is applied to it.
  • Each of the parallel resistors does not get the full current hence they divide it.

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Things To Remember

  • Resistors can be termed as the universal components in the electronic industry.
  • The reciprocal of resistance i.e. 1/R is used. 
  • Parallel resistance is smaller than any individual resistance in the combination.
  • Larger resistors with kilo-Ohm or mega-Ohm resistances are common.
  • The reciprocal of the equivalent resistance is equal to the sum of the reciprocals of each resistance.

Previous Year Questions

  1. A Circuit Contain Two Resistors R1 And R2 In Series…. [JIPMER 2019]
  2. Twelve Resistors Each Of Resistance 16 Are Connect…  [BITSAT 2019]
  3. Three Resistors 1 2 And 3 Are Connected To Form A… [VITSAT 2012]
  4. Three Equal Resistors Connected In Series Across A…. [NEET 1998]
  5. A Set Of N Equal Resistors Of Value R Each Are Con…  [NEET 2018]
  6. 13 Resistors Each Of Resistance R Are Connected In… [KCET 2003]
  7. Four Resistors Of 100 Each Are Connected In The Fo… [KCET 1996]
  8. Two Resistors Of Resistances 200 K And 1 M Respect… [KEAM]
  9. Four Resistors 100 Omega 200 Omega 300 Omega And 4…
  10. You Are Given N Resistors Each Of Resistance R The…  [GUJCET 2006]
  11. An Inductor Of Inductance L 400 Mh And Resistors…
  12. N Resistors Each Of Resistance R First Combine To…
  13. Two Resistors Of Resistances R 1 300 And R 2 500 A…
  14. All The Resistors Are Equal In Value Each Being 2…
  15. Wire Bound Resistors Are Made By…
  16. A Current Of 5a Is Passing Through A Metallic Wire… [VITEEE 2006]
  17. A 2 V Battery A 15 Resistor And A Potentiometer O… [JCECE 2011]
  18. Three Resistances Each Of 4 Are Connected To Form… [NEET 1993]
  19. Charge Passing Through A Conductor Of Cross Sectio… [VITEEE 2012]

Sample Questions

Ques 1. Define resistors in parallel. (2 Marks)

Ans. Resistors are either connected as a series or in a parallel pattern when both of their terminals are respectively connected to each terminal of the other resistor or resistors to create a more complex network. 

The voltage across the resistors for each resistor in a parallel pattern will be the same whereas the current will be in proportion to the resistance of each individual resistor. When resistors are connected in parallel, then the supply current is equal to the sum of the currents through each resistor.

Ques 2. Calculate the resultant resistance of a parallel circuit containing three resistors; R1 = 4Ω, R2 = 6Ω and R3 = 2Ω. (2 Marks)

Ans. Given value of resistors are,

R1 = 4Ω,

R2 = 6Ω,

R3 = 2Ω

\(\frac{1}{R_{Total}} =\frac{1}{R_1} + \frac{1}{R_2} + \frac{1}{R_3}.......\frac{1}{R_n}\)

1/Rp =(1/4) +(1/6)+(1/2)

1/Rp =11/12

Rp=12/11

Rp = 1.0909 Ω

Ques 3. State three features of resistors in parallel. (2 Marks)

Ans. The major features of the resistors in parallel are: 

  • Parallel resistance is smaller than any individual resistance in the combination.
  • Each parallel resistor has an equal amount of voltage of the source which is applied to it.
  • Each of the parallel resistors does not get the full current hence they divide it.

Ques 4. What is the equivalent resistance of a 1000 kilo-ohm and a 250 kilo-ohm resistor connected in parallel? (2 Marks)

Ans.  1/ 1eq = 1/R1 + 1/R2 

1/ 1eq = 1/1000 + 1/250

= 5/1000

Req

= 200 kilo−Ω

Ques 5. Mention a difference between the minimum and maximum effective resistance. (1 Mark)

Ans. Differences between the minimum and maximum effective resistance are: 

Minimum effective resistance is the least possible resistance of the circuit whereas maximum effective resistance is the total possible resistance of the circuit 

Ques 6. What is the series connection of resistors? (1 Mark)

Ans. The resistors are connected across the two points in the circuit in a structure that the current flowing through each resistor is the same and only one path is available for it to flow hence the resistors are said to be connected in series.

Ques 7. Is there any advantage of connecting electrical devices in parallel with the battery instead of connecting them in series? (1.5 Marks)

Ans. Yes, connecting electrical devices in parallel with the battery instead of connecting them in series has an advantage. A parallel circuit divides the current through electrical gadgets and total resistance in a parallel circuit is decreased. Therefore, it is helpful particularly when each gadget has different resistance and requires different current to operate properly.

Ques 8. Define electric resistivity material and do mention its SI Unit. (1.5 Marks)

Ans. The resistivity material is a resistance of a unit length of the conductor with the unit area of cross-section. SI Unit is ohm meter. 

Ques 9. what is the reciprocal resistance used to evaluate the equivalent resistance of a number of resistors in parallel? (1 Mark)

Ans. To find the equivalent resistance of a number of resistors in parallel, the reciprocal of resistance i.e. 1/R is used. 

Ques 10. What is a mixed combination of resistances? (1.5 Marks)

Ans. A mixed combination of resistance is a circuit including both series and parallel combinations.

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CBSE CLASS XII Related Questions

  • 1.
    A charged particle $+q$ in an electric field $\vec{E}$ experiences a force in the direction of the electric field. As a result, its kinetic energy changes. Similarly, the charged particle also experiences a force when it moves in a magnetic field $\vec{B}$. But this magnetic force is perpendicular to both velocity $\vec{v}$ of the charged particle and the magnetic field $\vec{B}$, so it cannot change the kinetic energy of the charged particle. Consider two charged particles 1 and 2 of masses $m$ and $\frac{m}{2}$ having charges $-q$ and $+2q$ respectively. They are accelerated from rest through the same potential difference $V$ and acquire kinetic energy $K_1$ and $K_2$. Then they enter in a region of uniform magnetic field $\vec{B}$ perpendicular to their velocities.


      • 2.
        This ‘average velocity’ is found be few mm/s for currents in range of a few amperes. How then is current established almost the instant a circuit is closed ?


          • 3.
            Read the following paragraph and answer the questions that follow.
            A p-type or n-type semiconductor can be converted into a p-n junction by doping it with suitable impurity. The motion of majority charge carriers causes diffusion current across the junction while the barrier electric field causes motion of minority carriers for drift current. In case of unbiased diode, the diffusion and drift currents are equal. This equilibrium is disturbed by the biasing batteries. Diodes, therefore, allow currents in one direction. This property of diode is used in making rectifiers.


              • 4.
                An electric field $\vec{E}$ is established across the ends of a cylindrical conductor of length L and area of cross-section A. Discuss how electrons attain an average velocity, independent of time. Hence, obtain a relation between current in the conductor and this ‘average velocity’ of electrons.


                  • 5.
                    Capacitors are manufactured with certain standard capacitances and working voltages. However, these standard values may not be the ones that are actually needed in a particular application. Two or more capacitors can be grouped in series or in parallel to achieve desired capacitance and voltage. When connected in series, the total capacitance decreases while the voltage rating increases, whereas in parallel connections, the total capacitance increases and maintains the same voltage rating. A capacitor stores energy in the electric field between its plates and stored energy is proportional to the square of the voltage and capacitance $U = \frac{1}{2}CV^2$, where symbols have their usual meanings.
                    Two capacitors, one of $3 \ \mu$F and the other of $6 \ \mu$F, are connected in series in the circuit as shown in the figure, for a long time. }


                      • 6.
                        Derive an expression for the capacitance of a parallel plate capacitor of plate area A and plate separation d with air present between the plates.

                          CBSE CLASS XII Previous Year Papers

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