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In the following schematic, if

  • R1 = 42ohm,
  • R3 = 33ohm,
  • VT = 220V, and
  • IR2 = 1A

How do I find R2?

schematic

simulate this circuit – Schematic created using CircuitLab

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  • 5
    \$\begingroup\$ Algebra. Let 'I1' be the current through R2. Ohms law. parallel resistances 1/RP=1/R1+1/R2 etc. Now do your homework:) \$\endgroup\$ – Martin James Jun 3 '14 at 15:34
  • \$\begingroup\$ I do not understand by Let"I1" be the current through R2 \$\endgroup\$ – user2463158 Jun 3 '14 at 15:38
  • \$\begingroup\$ Asking us to solve what looks like a homework problem is off-topic for this site as it doesn't help anyone: you or us. If you have a specific question about some aspect of the problem, then please update your question. Otherwise I expect this question will likely be closed soon. \$\endgroup\$ – Adam Head Jun 3 '14 at 15:58
  • \$\begingroup\$ This is not a homework problem, I took it from a electronic book which i unable to solve \$\endgroup\$ – user2463158 Jun 3 '14 at 16:14
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\$ I_{R2} = 1 \text{ amp}\$, \$ R1 = 47 \Omega \$, \$ R3 = 33 \Omega \$, \$VT = 220 \text{ volt} \$

Now since R1 and R2 are in parallel

$$ I_{R1} \cdot R1 = I_{R2} \cdot R2 $$

Solve to find \$I_{R1}\$ then substitute in

$$ I_{R2} \cdot R2 + \left( I_{R1} + I_{R2} \right) \cdot R_3 = VT $$

The rest is basic arithmetic. If your having problems post what you have tried but you won't learn if one of us does it for you.

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  • \$\begingroup\$ u mean IR1 = (1*R2)/47 but idk r2 \$\endgroup\$ – user2463158 Jun 3 '14 at 16:03
  • \$\begingroup\$ When you put that into the second equation you have only R2 unknown and should be able to calculate it from there. \$\endgroup\$ – Warren Hill Jun 3 '14 at 16:15

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