Discussion
Its input resistance at the base with \( \beta = 200 \) is about
Answer: C
The emitter resistance is reflected to the base multiplied by the gain:
\[ \begin{aligned} r_{\pi} &= \beta r_{e} \\ &= 200 \times 52 \\ &= 10.4 \ \mathrm{k\Omega} \end{aligned} \]
so about 10.4 kilohms, and the bias divider will usually be in parallel with it and may well dominate. Two quantities multiply here, one of which is unreliable, which is why input impedance is a far less predictable specification than gain. Most errors on this topic come from carrying a result across from a neighbouring scheme where it does not hold. Most errors on this topic come from carrying a result across from a neighbouring scheme where it does not hold.
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