Unit 2                                                       

1270                              PRACTICE EXAM SOLUTION Prob 2                                     

 

2.     

                             

 

         Find the Thevenin's equivalent circuit at terminals a-b. Hint: Use node voltage method to find VTh.

 

Solution:

 

            

 

        

         First, we find VTh by node-V method (with nothing connected at a-b). We have one node, v1, to write an equation for: (VTh = v1 no load)

 

                                            

 

         We have ix = . Substitute this into our equation

 

                                            

 

         or

 

                                            

 

         Multiply both sides by R1R2:

 

                                            

 

                                                       

 

 

         To find RTh, we have two possible approaches:

 

         1.      Find current in wire shorting a to b. Then use RTh = .

         2.      Connect V source to ab with independent source vs = 0.

                  Then use RTh = where i = current flowing into "a" terminal.

         We'll use the second approach. Set vs = 0V. Connect 1 V source to a-b. Then

 

                  =