# Homework Help: Electrical Circuits - Find the power and Voltage

1. Sep 10, 2011

### VitaX

1. The problem statement, all variables and given/known data

[PLAIN]http://img143.imageshack.us/img143/3746/electriccircuits.png [Broken]

2. Relevant equations

3. The attempt at a solution

Can someone help me with part B of this? I understand that in part a it says the 5 A source is delivering 10 W of power, so that would in turn make the positive terminal of the source at the top, since its delivering power. X1 is absorbing power which would mean it takes in through the positive terminal and leaves through the negative. For part b I get that the 2 V is constant throughout the circuit since its closed so the Power at the 3 A source is 6 W. But I'm having a hard time understanding why the Power at the element X1 is 4 W according to the books answer. My main concern is following the current flow here, I mean isn't the 2 Volts going through the element X1? I'm just having a hard time understanding the diagram.

Last edited by a moderator: May 5, 2017
2. Sep 10, 2011

### phinds

voltage does go through X1, current does.

I the 3A source delivering power or absorbing power? How can you tell?

3. Sep 10, 2011

### VitaX

Well you could only tell if the polarities were in place, but that's also what I'm having trouble discerning. How do I break down the circuit just to analyze part b of the problem? The book's answer for part b is Power in the 3 A source = 6 W (absorbed), Power in the element X1 = 4 W (absorbed). One of my main problems are the two sources. Isn't there 5 Amps and 3 Amps running through the element X1 at the same time?

Edit: I just overlooked the loop equation to find the polarity of the 3 Amp source. So in using that I get the positive terminal on the top and negative terminal on the bottom of the 3 Amp source. And judging by the current flow in the 3 Amp source, it will be absorbing 6 W of power. Main problem now is finding the power going through X1.

Edit 2: Nevermind, it's just sum of power absorbed = sum of power released ; 6 + p1 = 10

Last edited: Sep 10, 2011
4. Sep 10, 2011

### phinds

My original statement should have been (as you no doubt figured out) "voltage does NOT go through ... "

Why is it a problem for there to be 5 amps in one supply and 3 amps in the other with something different than 8 amps going through X1? Do you understand the clearly shown direction of the current flows? As for the polarity, you have aleady figured that out and there is nothing more to figure out except how to divide up the currents as they enter/exit the 3 lines coming into the top of X1