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hkhandrika
#1
Mar23-05, 10:17 PM
P: 15
The problem is:

The current I through the 4.0 k-ohm resistor in Fig. 26-42 is 6.50 mA. What is the terminal voltage Vba of the "unknown" battery? (There are two answers.)

The two answers depend on the direction of the current. Here is the picture:

http://home.san.rr.com/hkhandrika/26-42.gif

First I looked at the 4.0 k-ohm resistor and said that the 8.0 k-ohm resistor had 1/2 the current flowing thru it, then I added up the parallel resistors to get one that was (8/3)k-ohm with 9.75 mA of current going thru it.

I thought I could use this current and then say that the voltage at point B (if you go left) would be 9.75mA * the 8/3 resistor + 9.75 * the 5 k-ohm resistor. But then how would you figure out the voltage at point A? If you go right, could you then do 9.75mA * 8/3 resistor - 12V and set that equal to Va, and then add 9.75 mA * the 5 k-ohm resistor and say that's the voltage at B? I tried this, and my answer is incorrect. I am doing this on webassign so I can see whether my answer is wrong or not, but I dont have the solutions to this problem.

Am I doing the process correctly in the first place? Any help would be greatly appreciated.

Thank you for your time and effort.
Attached Thumbnails
26-42.gif  
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