Question

A change of $400mV$ in base-emitter voltage causes a change of $200$$\mu A$ in the base current. The input resistance of the transistor is

• A. $1K$$\Omega$
• B. $6K$$\Omega$
• C. $2K$$\Omega$
• D. $8K$$\Omega$

Answer 1

The correct option is C $2K$$\Omega$

Given that:
$V_{BE}=400mV=4\times {10}^{-1}V$

$I_B=200\mu A=2\times {10}^{-4}A$

The input resistance of the transistor is
$r_i=\frac{V_{BE}}{I_B}$

$r_i=\frac{4\times {10}^{-1}}{2\times {10}^{-4}}$

$r_i=2\times {10}^3=2K\Omega$