P 3.5-1 Determine the power supplied by each source in the circuit shown in Figure P 3.5-1.

 

Figure P 3.5-1

To find the power supplied by each source we need the current through and the voltage across each one.  First we simplify the circuit by combining the two voltage sources and combining the two current sources.  Then we can get the voltage across the two current sources as they are in parallel and we can get the current through the two voltage sources as they are in series.  So the new combined circuit looks like:

We have one junction equation

And we have one loop equation, starting at lower left and going clockwise around the outer loop.

 

Multiply first equation by 2 Ω and rearrange the second one and we can add the two equations

 

Adding them we get

Solve for

 

Solving for

 

- sign means current goes other way then drawn.

 

So use the  current for the current going through the two voltage sources.   can be used with the 2 Ω resistor to determine the voltage across the two current sources.  The fact that the current is going up through the resistor means the bottom side of the circuit is more positive than the top side.

 

 

Now we just have to watch polarity to determine if power is being supplied (> 0) by the source or being absorbed (< 0) by the source.

 

 

 

 

 

 

 

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This page last updated on January 19, 2019