Node Voltage Method: Find Voltage Across 6A Current Source

[Marcin H]

Homework Statement

Find the voltage, V, across the 6A current source

Homework Equations

V=IR
Node Voltage Method

The Attempt at a Solution

Did I set this up correctly to find my voltage?

 

[gneill]

Almost. Be careful of the signs of the terms.

Judging by the sign you gave to the 6A supply term you're summing currents leaving the node. So why are your last two terms negative?

 

[Marcin H]

Almost. Be careful of the signs of the terms.

Judging by the sign you gave to the 6A supply term you're summing currents leaving the node. So why are your last two terms negative?

Oh, woops. Read the polarities incorrectly. So if I change the last 2 to positive, it's good?

 

[gneill]

Yes, that would be a correct expression. Make it an equation by setting it equal to zero

 

[Marcin H]

Yes, that would be a correct expression. Make it an equation by setting it equal to zero

Thanks!

 

[Marcin H]

Yes, that would be a correct expression. Make it an equation by setting it equal to zero

Got stuck again! The next question asks "What is the power associated with the 10V source?" I can find it using P=IV=I^2R=V^2/r, but how do I find the current through the 10V source?

 

[gneill]

Each term in the node equation represents a branch current. One of the terms corresponds to that current. Pick it out and use it now that you've found the node voltage.

 

[Marcin H]

Each term in the node equation represents a branch current. One of the terms corresponds to that current. Pick it out and use it now that you've found the node voltage.

Ohh. So I use (Vx-10)/20= (36-10)/10 = 2.6A And then using P=IV I can do (2.6A)(10V)= 26W***?

 

[gneill]

That would be the idea, yes.

 

[Marcin H]

That would be the idea, yes.

Ok thanks! 13W***

 

[gneill]

Check your calculation for the current. (36 - 10)/10 = ?

 

[Marcin H]

Ohh. So I use (Vx-10)/20= (36-10)/10 = 1.3A And then using P=IV I can do (1.3A)(10V)= 13W***?

Check your calculation for the current. (36 - 10)/10 = ?

Woops! 26 watts.

 

[gneill]

Woops! 26 watts.

Try again. Show your calculations.

 

[Marcin H]

Try again. Show your calculations.

What? Where did I go wrong? I = (36-10)/10 = 26/10 = 2.6A. Using that current and P=IV I can find the power in the 10V source. P = (2.6A)(10V) = 26 Watts

 

[Marcin H]

What? Where did I go wrong? I = (36-10)/10 = 26/10 = 2.6A. Using that current and P=IV I can find the power in the 10V source. P = (2.6A)(10V) = 26 Watts

ORIGINAL QUESTION: what is the power associated with the 10V source?

 

[gneill]

ORIGINAL QUESTION: what is the power associated with the 10V source?

Ah. My mistake. Sorry. I was thinking of the power associated with the branch as a whole. You have the correct result.