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enter image description here

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

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  • \$\begingroup\$ Is node B is connected to +5V ? \$\endgroup\$ – nidhin Apr 4 '15 at 17:39
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    \$\begingroup\$ Such homework questions with no attempt at a solution are closed. \$\endgroup\$ – Leon Heller Apr 4 '15 at 17:45
  • \$\begingroup\$ I don't really get how Vab becomes 0.2V!! \$\endgroup\$ – nidhin Apr 4 '15 at 17:54
  • \$\begingroup\$ @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. \$\endgroup\$ – Roger C. Apr 4 '15 at 18:13
  • \$\begingroup\$ @RogerC. yup. got it. read something in schematic in a wrong way :) \$\endgroup\$ – nidhin Apr 4 '15 at 19:04
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The answer is 200 ohm... Check the image below enter image description here

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    \$\begingroup\$ If it is not possible to type the answer please rotate the image. \$\endgroup\$ – nidhin Apr 4 '15 at 18:54
  • \$\begingroup\$ Rotated now... Tell if you can understand now ;) \$\endgroup\$ – pfxr Apr 4 '15 at 19:43
  • \$\begingroup\$ 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\$. \$\endgroup\$ – Roger C. Apr 4 '15 at 19:56
  • \$\begingroup\$ oh... right, I'll fix it and edit the comment later. Thanks Roger \$\endgroup\$ – pfxr Apr 4 '15 at 20:15
  • \$\begingroup\$ Fixed it... Again, sorry for the bad answer and thanks @RogerC. \$\endgroup\$ – pfxr Apr 4 '15 at 21:46

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