Silicon diode conduction check: If the external polarity matches the diode orientation and the measured potential difference across a silicon diode exceeds about 0.7 V, the diode is considered:

Introduction / Context:
Technicians often assess diode orientation and bias using quick multimeter checks. For silicon PN diodes, forward conduction typically begins around 0.6–0.7 V at room temperature. Recognizing this threshold allows rapid fault isolation in rectifiers, clamp circuits, and logic protection paths.

Given Data / Assumptions:

• Silicon diode (not Schottky or germanium).
• Polarity applied in the forward direction.
• Observed potential difference (PD) > 0.7 V.

Concept / Approach:
Forward bias reduces the depletion region, allowing majority carriers to cross the junction. The diode’s I–V curve shows an exponential rise in current beyond approximately 0.7 V (silicon), with exact value depending on temperature and current level. Therefore, a PD above ~0.7 V with matching polarity indicates forward bias and conduction.

Step-by-Step Solution:
Check polarity: anode at higher potential than cathode.Measure PD: if around or above ~0.7 V, carriers are injected; current flows.Conclude operational state: diode is forward biased.Expect some temperature dependence: hotter junction → slightly lower forward voltage.

Verification / Alternative check:
Most DMMs have a diode-test mode; a good silicon junction typically reads 0.6–0.7 V in forward direction, and OL (open) in reverse for low test currents.

Why Other Options Are Wrong:
Not working / open switch: contradicts evidence of forward conduction.Reverse biased: would show near-zero current and high resistance at low voltage.

Common Pitfalls:
Confusing Schottky diodes (forward drop ~0.2–0.4 V) and germanium (~0.3 V) with silicon. Always consider device type and temperature.

Final Answer:
forward biased