# Can someone help me with 2 circuit problems...please

by supermenscher
 Sci Advisor HW Helper P: 2,586 I would suggest using [ code ] and [ / code ] tags:  55 Ohms _____\/\/\/\/_____ | | 12 Ohms | | A | | .____/\/\/\_______ | |______. B | | | | |____\/\/\/\/_____| R V1=9.0V R1 --+B--/\/\/\------- | | | R2 | .-----/\/\/\/-------. | | | | |----------B+------| V2=6.0V EDIT: Well, it looks best in the editor window, slightly better (but not great) in the code tags, and unreadable without those tags. SECOND EDIT: looks fine now ------------------------------------------------------------ For the first question, you should know how to calculate net resistances when you have resistors in series and parallel. To find the total resistance between A and B, it is: $$R_{total} = 12 \Omega + (55 \Omega || R)$$ $$38 \Omega = 12 \Omega + (\frac{1}{55 \Omega} + \frac{1}{R})^{-1}$$ $$26 \Omega = (\frac{1}{55 \Omega} + \frac{1}{R})^{-1}$$ $$(\frac{1}{26 \Omega} - \frac{1}{55 \Omega})^{-1} = R$$ $$R \approx 49.310 \Omega$$ $$R = 49 \Omega$$ ----------------------------------------------------------- Solve question 2 using the principle of superposition. That is, find the voltages and currents with the circuit first by replacing the top battery with a short circuit, then find the voltages and currents with the top battery, replacing the bottom with a short circuit. Add the numbers from the first calculations to the second calculations, and make sure you take direction/sign into account.