Question

For the given circuit, if current amplification factor $\beta=90$ and $V_{B E}=0.7 \, V$

Then, base resistance $R_{B}$ is

• A. $180 \, k \Omega$
• B. $185 \,k \Omega$
• C. $82 \, k \Omega$
• D. $190 \,k \Omega$

Answer 1

Answer: (C)

From Kirchhoff's loop rule in output loop,
$9-4 =I_{C} R_{C} $
As, $ R_{C} =2 k \,\Omega, $
$\Rightarrow I_{C} =\frac{5}{2 \times 10^{3}}=2.5\, mA $
$ \Rightarrow I_{B}=\frac{I_{C}}{\beta}=\frac{2.5}{90}=27.8\, \mu A$
$V_{B E} =0.7\, V$
From Kirchhoff, loop rule in input loop,
$I_{B} R_{B}=3-0.7$
$ \Rightarrow R_{B}=\frac{2.3}{27.8} \times 10^{6}=82 \,k \Omega$