Multiple choice

An amplifier without feedback has a voltage gain of 50, input resistance of 1 K$\Omega$ and output resistance of 2.5 K$\Omega$. The input resistance of the current-shunt negative feedback amplifier using the above amplifier with a feedback factor of 0.2, is

  1. $\dfrac{1}{11}$ K$\Omega$
  2. $\dfrac{1}{5}$ K$\Omega$
  3. 5 K$\Omega$
  4. 11 K$\Omega$
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A Correct answer
Explanation

$$ \text{We have} R_i = 1K\Omega, \beta = 0.2, A =50 \\

Thus, \qquad R_{if} = \dfrac{R_i}{{(1+A\beta)}} = \dfrac{1}{11} K \Omega $$-

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