Independent current and voltage network analysis

[qizzlestick]

Homework Statement

there's two current sources and three voltages sources the problem wants to know the power supplied by each current source

Homework Equations

according to the book the problem can be solved using Kirchoffs current law and kirchhoffs voltage law

The answers according to the textbook the 2mA current source supplies 6mW and the 1 mA current source supplies -7mW

The Attempt at a Solution

I can only guess that they subtract the 5v by the 8v then multiply the result by the 2mA.
Also subtract the 15v by the 8v and multiply the result by the 1mA source to get the -7mW answer.

 

[vela]

The Attempt at a Solution

I can only guess that they subtract the 5v by the 8v then multiply the result by the 2mA.
Also subtract the 15v by the 8v and multiply the result by the 1mA source to get the -7mW answer.

This is correct, but can you explain why? (I'm not sure about the signs though. I think they should be -6 mW and +7 mW, but I could be wrong.)

 

[NascentOxygen]

The +8v source sets the voltage between the far left and far right nodes to be 8v, with the left node positive. No IF's or BUT's about it.

 

[crixus]

Best way to approach such ckt problems is to assume a reference node and assign a zero potential to it.Next move across the branches and assign voltages to other nodes by appropriately adding or subtracting voltages keeping in mind you assign movin from lower potential to higher potential a PLUS sign. Then you would have got voltages at all nodes then evaluate power using V*I . Power is being supplied or is positive if current is flowin from higher potential to lower potential and dissipated if vice versa.

Hope its clear now