What is the value of \( V_{o} \) if the silicon diode starts conducting at 0.7 V while the germanium starts conducting at 0.3 V?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 11.7 V
A diode conducts only when the forward voltage across it reaches its cut-in voltage, after which the voltage across it stays at about that value.
The Si and Ge diodes are in parallel, both forward biased by the 12 V cell, so they always have the same voltage across them. As the voltage rises, the Ge diode reaches 0.3 V first and starts conducting. It then holds the voltage across the pair at 0.3 V, so the Si diode never reaches 0.7 V and stays off (\( I_1 = 0 \)).
The rest of the cell voltage appears across the \( 5\,\mathrm{k}\Omega \) resistor:
\( V_{o} = 12\,\mathrm{V} - 0.3\,\mathrm{V} = 11.7\,\mathrm{V} \)