# Series and Parallel Circuit

In the following schematic, if

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

How do I find R2?

simulate this circuit – Schematic created using CircuitLab

• Algebra. Let 'I1' be the current through R2. Ohms law. parallel resistances 1/RP=1/R1+1/R2 etc. Now do your homework:) – Martin James Jun 3 '14 at 15:34
• I do not understand by Let"I1" be the current through R2 – user2463158 Jun 3 '14 at 15:38
• 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. – Adam Head Jun 3 '14 at 15:58
• This is not a homework problem, I took it from a electronic book which i unable to solve – user2463158 Jun 3 '14 at 16:14

## 1 Answer

$I_{R2} = 1 \text{ amp}$, $R1 = 47 \Omega$, $R3 = 33 \Omega$, $VT = 220 \text{ volt}$

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.

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