VINAY RAO
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@Alexander: Thank you for your reply. I repeat here again, the problem which i posted is not a home work problem. Getting to know the procedure to solve these type of problems only helps me to strengthen my basic understandings. Still my doubts are not cleared yet.
part a) When Rsig changes: If Rsig changes then surely vi also changes then CURRENTin also changes. Do you feel like, the changes in vi and the current (which is flowing into the two port) is same hence Rin doesn't change or bcz of any other reason?
part b) When RL changes: When this happens, vo changes hence similarly Av (But Avo is constant) and also vi. As vi changes and also the current (into two port)and hence Rin has to be changed. But the problem here is that, neither i know vo nor vi or the current flowing in to the two port => unknowns are vi,vo,Rin,current (into two port) when load is connected. How can i find Rin with these many unknowns (only known thing is Av which can be calculated from Avo, Ro and RL)?
Note: if i assume Rin to be constant (As you told to keep every parameter constant)then it doesn't match the answers given. In part (b) & (c) of exercise 4.31, Rin also changed by changing RL.
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