Unit 2                                                       

1270                              PRACTICE EXAM SOLUTION Prob 3                                     

 

3.     

                              

 

         Calculate the power furnished or absorbed by the 30V voltage source, and state whether it is furnished or absorbed.

 

Solution:

 

         Because there are several current sources, the node-V method is a good choice here. For node v1:

 

                                         

 

 

         Our constraint equation: . Substitute this into the node v1 equation:

 

                                         

 

         or

                                         

 

         or

                                         

 

         or

                                         

 

         Current i flowing from + to - in 30 V source:

 

                                         

 

                                          Power = furnished

 

                                          Power 120 W furnished (or delivered)

 

         Check: Calculate all i's and v's and verify Kirchhoff's laws.

 

                      

 

                                           All sums of currents out of nodes = 0 A

 

                                          All sums of V-drops around loops = 0 V