
#1
Jan2009, 07:09 PM

P: 2

1. The problem statement, all variables and given/known data
Find the power absorbed by element X, if it is 4000 Ohms. (See attached picture for circuit) 2. Relevant equations KCL: Sum of Currents into Node Must = 0 3. The attempt at a solution I've already worked through a bunch of these type of problems, but I always mess up on which currents are positive and which ones are negative...which ultimately leads to the wrong answer. I know on this specific problem, the whole idea is to apply KCL in order to obtain a Voltage. That voltage will then be multiplied by 40 Ohms to give you the power absorbed by the resistive element. I think my lack of understanding of KCL is keeping from getting these ideas. I guess as I run this problem through my head I use a reference location at the node above the 1000 Ohm resistor. And from my thinking I would come up with the following equation... 0=(.08)A  (v/1000[ohms])A  (.03)A  (v/4000[ohms])A Then I would solve for V, but it ends up giving me the wrong answer. I'm assuming one of my values should be negative? 



#2
Jan2009, 08:51 PM

P: 2

Nevermind! Figured it out. The equation above is correct, it's when I was adding and subtracting to the opposing sides, I kept seeing .08A as .08A.
It computes out to 40V on the Resistor. Then I use P=V2/R to obtain .4 Watts. 


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