# help solving circuit [closed]

I'm looking for help solving this circuit. what is the value of the resitor R4, knowing the Voltage between points A and B ( Vab=0,2V). thanks

• Is node B is connected to +5V ? – nidhin Apr 4 '15 at 17:39
• Such homework questions with no attempt at a solution are closed. – Leon Heller Apr 4 '15 at 17:45
• I don't really get how Vab becomes 0.2V!! – nidhin Apr 4 '15 at 17:54
• @nidhin there is a voltage drop in R3. Therefore the potential of B (relative to ground) is below 5V. Actually it will be below the potential in A by 0.2 V for some R4 value. – Roger C. Apr 4 '15 at 18:13
• @RogerC. yup. got it. read something in schematic in a wrong way :) – nidhin Apr 4 '15 at 19:04

• In your equation you have $V_{AB}=V_A-V_B=0.2 V$ which is correct, but then you have a sign error isolating $V_B$ because $V_B=-0.2+0.6 V$ and not $0.2+0.6$. – Roger C. Apr 4 '15 at 19:56