In the above systems in each ease A B C 2 arbitrary terminal

In the above systems, in each ease (A, B, C) 2 arbitrary terminals 1 and 2 have been pulled out from the boxes. Thevenin\'s Theorem says that (provided certain conditions are fulfilled), between the terminals 1 and 2, the circuit inside the box A can be replaced by an equivalent circuit consisting of a single voltage source V, in series with a single resistance R, where V is the open circuit voltage across 1 and 2, and R is the resistance seen at terminals 1 and 2 with all the voltage sources inside the box short circuited and all the current sources open circuited. For the circuits in B and C tell if the Thevenin\'s Theorem holds or not, and very briefly give your reasoning why or why not. For C assume that ambient temperature T is held constant while trying to find Thevenin\'s equivalent circuit. Suppose while measuring the open circuit voltage and short circuit current (at terminals 1 and 2 in the systems A, B, or C above) if you see both the open circuit voltage and the short circuit current arc equal to zero, what will that imply and what kind of things do you think are inside that box in that case?

Solution

Thevenin\'s theorem states that any combination of volatge sources and resistances can be represented as a single voltage and current source. If the short circuit current is zero ideally the resistance has to be infinite, and open circuit voltage can be zero when ideally the resistance is along the voltage source. For B and C, thevenins theorem holds good.