In a CE transistor when the base current increases by 60 $\mu \mathrm{A}$, change in base-emitter voltage is…

In a CE transistor when the base current increases by 60 $\mu \mathrm{A}$, change in base-emitter voltage is $1.2 \mathrm{~V}$. Then the input resistance is
  1. $1000 \Omega$
  2. $5000 \Omega$
  3. $2000 \Omega$
  4. $20000 \Omega$

Solution

$\begin{aligned} & \text { } \mathrm{I}_{\mathrm{b}}=60 \mu \mathrm{A}=60 \times 10^{-6} \mathrm{~A} \\ & V_{\mathrm{BE}}=1.2 \mathrm{~V} \\ & \mathrm{~V}_{\mathrm{BE}}=\mathrm{I}_{\mathrm{b}} \mathrm{R}_{\text {in }} \\ & \Rightarrow \mathrm{R}_{\text {in }}=\frac{\mathrm{V}_{\mathrm{BE}}}{\mathrm{I}_{\mathrm{b}}}=\frac{1.2}{60 \times 10^{-6}}=20000 \Omega\end{aligned}$

Asked in: AP EAMCET 2023 (19 May Shift 1)

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