Question

Ge and Si diodes conduct at 0.3 V and 0.7 V respectively. In the following figure if Ge diode connection are reversed, the valve of $V_0$ changes by

• A. 0.2 V
• B. 0.4 V
• C. 0.6 V
• D. 0.8 V

Answer 1

The correct option is B 0.4 V

Consider the case when Ge and Si diodes are connected as show in the given figure.
Equivalent voltage drop across the combination Ge and Si diode = 0.3 V
$\Rightarrow$ Current $i=\frac{12-0.3}{5k\Omega }=2.34mA$
$\therefore$ Out put voltage $V_0=Ri=5k\Omega \times 2.34mA=11.7V$
Now consider the case when diode connection are reversed. In this case voltage drop across the diode's combination = 0.7 V
$\Rightarrow$ current $i=\frac{12-0.7}{5k\Omega }=2.26mA$
$\therefore V_0=iR=2.26mA\times 5k\Omega =11.3V$
Hence charge in the value of $v_0$ = 11.7 - 11.3 = 0.4 V