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GATE 2019 EC – Question 14

Networks, Signals and Systems · Two-Port Networks and Wye-Delta Transformation · 1 mark · Multiple choice

Consider the two-port resistive network shown in the figure. When an excitation of 5 V is applied across Port 1, and Port 2 is shorted, the current through the short circuit at Port 2 is measured to be 1 A (see (a) in the figure).

Now, if an excitation of 5 V is applied across Port 2, and Port 1 is shorted (see (b) in the figure), what is the current through the short circuit at Port 1?

Diagram for GATE 2019 EC question 14
  1. 0.5 A
  2. 1 A
  3. 2 A
  4. 2.5 A

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Show answer and explanation

Correct answer: (B) 1 A

Explanation

The network is made of resistors only, so it is reciprocal. For a reciprocal network, $\frac{I_2}{V_1}\Big|_{V_2=0}=\frac{I_1}{V_2}\Big|_{V_1=0}$, so the same 5 V at Port 2 gives the same 1 A at Port 1.