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Current Electricity question

2022 · 24 Jun · Shift 2 · Q51
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Current Electricity question

2022 · 24 Jun · Shift 2 · Q51

JEE MainPhysicsCurrent ElectricityMCQ+4 / −1
What will be the most suitable combination of three resistors A = 2 Ω\OmegaΩ, B = 4 Ω\OmegaΩ, C = 6 Ω\OmegaΩ so that (223)\left( {{{22} \over 3}} \right)(322​) Ω\OmegaΩ is equivalent resistance of combination?
  1. A
    Parallel combination of A and C connected in series with B.
  2. B
    Parallel combination of A and B connected in series with C.
  3. C
    Series combination of A and C connected in parallel with B.
  4. D
    Series combination of B and C connected in parallel with A.
View written solutionFree

Correct answer: B

  1. We are given three resistors: A=2 Ω,B=4 Ω,C=6 ΩA=2\,\Omega,\quad B=4\,\Omega,\quad C=6\,\OmegaA=2Ω,B=4Ω,C=6Ω We need the combination whose equivalent resistance is 223 Ω\frac{22}{3}\,\Omega322​Ω

  2. Check each option one by one.


Option A

Parallel combination of AAA and CCC, connected in series with BBB.

First, equivalent of A∥CA \parallel CA∥C: RAC=A⋅CA+C=2⋅62+6=128=32 ΩR_{AC}=\frac{A\cdot C}{A+C}=\frac{2\cdot 6}{2+6}=\frac{12}{8}=\frac{3}{2}\,\OmegaRAC​=A+CA⋅C​=2+62⋅6​=812​=23​Ω

Now add B=4 ΩB=4\,\OmegaB=4Ω in series: Req=32+4=32+82=112 ΩR_{eq}=\frac{3}{2}+4=\frac{3}{2}+\frac{8}{2}=\frac{11}{2}\,\OmegaReq​=23​+4=23​+28​=211​Ω

112=5.5 Ω≠223 Ω\frac{11}{2}=5.5\,\Omega \neq \frac{22}{3}\,\Omega211​=5.5Ω=322​Ω So, Option A is incorrect.


Option B

Parallel combination of AAA and BBB, connected in series with CCC.

First, equivalent of A∥BA \parallel BA∥B: RAB=A⋅BA+B=2⋅42+4=86=43 ΩR_{AB}=\frac{A\cdot B}{A+B}=\frac{2\cdot 4}{2+4}=\frac{8}{6}=\frac{4}{3}\,\OmegaRAB​=A+BA⋅B​=2+42⋅4​=68​=34​Ω

Now add C=6 ΩC=6\,\OmegaC=6Ω in series: Req=43+6=43+183=223 ΩR_{eq}=\frac{4}{3}+6=\frac{4}{3}+\frac{18}{3}=\frac{22}{3}\,\OmegaReq​=34​+6=34​+318​=322​Ω

This matches the required value. So, Option B is correct.


Option C

Series combination of AAA and CCC, connected in parallel with BBB.

First, equivalent of AAA and CCC in series: RAC=2+6=8 ΩR_{AC}=2+6=8\,\OmegaRAC​=2+6=8Ω

Now this is in parallel with B=4 ΩB=4\,\OmegaB=4Ω: Req=8⋅48+4=3212=83 ΩR_{eq}=\frac{8\cdot 4}{8+4}=\frac{32}{12}=\frac{8}{3}\,\OmegaReq​=8+48⋅4​=1232​=38​Ω

83 Ω≠223 Ω\frac{8}{3}\,\Omega \neq \frac{22}{3}\,\Omega38​Ω=322​Ω So, Option C is incorrect.


Option D

Series combination of BBB and CCC, connected in parallel with AAA.

First, equivalent of BBB and CCC in series: RBC=4+6=10 ΩR_{BC}=4+6=10\,\OmegaRBC​=4+6=10Ω

Now this is in parallel with A=2 ΩA=2\,\OmegaA=2Ω: Req=10⋅210+2=2012=53 ΩR_{eq}=\frac{10\cdot 2}{10+2}=\frac{20}{12}=\frac{5}{3}\,\OmegaReq​=10+210⋅2​=1220​=35​Ω

53 Ω≠223 Ω\frac{5}{3}\,\Omega \neq \frac{22}{3}\,\Omega35​Ω=322​Ω So, Option D is incorrect.


  1. Therefore, the only suitable combination is: Option B\boxed{\text{Option B}}Option B​

  2. Comparison with stored correct answer:

  • Stored correct answer: B
  • Derived answer: B

So, the derived answer agrees with the stored correct answer.

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