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In the given network, \(Z_{11}\) is equal to

Two-port network: 2 ohm series resistor at the input, shunt branch of a 4 ohm resistor in series with a dependent source 10 E1 (plus at the bottom), and a series resistor at the output; E1, I1 at the input and E2, I2 at the output

  • A.\(\frac{-6}{11}\) Ohm
  • B.\(\frac{6}{11}\) Ohm
  • C.\(\frac{4}{11}\) Ohm
  • D.\(\frac{2}{11}\) Ohm

Answer: B

The input impedance with the output open (\(I_2 = 0\)) is \(Z_{11} = E_1/I_1\), which is \(\frac{6}{11}\) ohm (option B). With the output open, the loop holds the 2 ohm and 4 ohm resistors and the dependent source, whose plus terminal is at the bottom.

\[ E_1 - 2I_1 - 4I_1 + 10E_1 = 0 \]

\[ 11E_1 = 6I_1 \]

\[ Z_{11} = \frac{6}{11}\ \Omega \]

The value \(-\frac{6}{11}\) (A) comes from taking the source with the opposite polarity, which would give \(1 - 10 = -9\) in the denominator, not 11. The other two values do not follow from the loop.

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