Discussion
That amplifier's input impedance was \( 2 \ \mathrm{k\Omega} \) open loop. With voltage series feedback it becomes
Answer: B
Series feedback multiplies the input impedance by one plus the loop gain:
\[ Z_{if} = 2\mathrm{k} \times 11 = 22 \ \mathrm{k\Omega} \]
giving 22 kilohms. Two hundred ohms would be the result of dividing, which is what shunt feedback does. The same factor of eleven appears in the gain reduction, the impedance rise and the distortion improvement, which is why computing the loop gain first answers every question about the circuit. A limit that survives making every external component ideal is an intrinsic one, and worth knowing for that reason.
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