Physics Electronics PMDC Conceptual Practice
PMDC Verified Question 47 of 494
When testing a healthy, functioning silicon \(\text{p-n}\) junction diode using the diode-test mode of a digital multimeter (DMM):
A
It reads approximately \(0.6\text{ to }0.7\text{ V}\) in forward bias and indicates 'OL' (overload/open) in reverse bias
B
It reads zero ohms in both forward and reverse bias directions
C
It reads 'OL' (open circuit) in both forward and reverse bias directions
D
It reads approximately \(0.6\text{ to }0.7\text{ V}\) in reverse bias and \(0\text{ V}\) in forward bias
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: It reads approximately \(0.6\text{ to }0.7\text{ V}\) in forward bias and indicates 'OL' (overload/open) in reverse bias
Concept:

A digital multimeter in diode-test mode applies a small constant current. In forward bias, it measures the forward junction voltage drop (approx. \(0.6-0.7\text{ V}\) for Si, \(0.2-0.3\text{ V}\) for Ge). In reverse bias, the diode blocks current, prompting the meter to display 'OL' (over-limit/open circuit).

Formula:

Qualitative concept / No formula required.

Solution:

  • Forward Bias: Anode connected to positive probe, cathode to negative probe \(\implies\) measures knee drop \(\approx 0.6\text{ to }0.7\text{ V}\).


  • Reverse Bias: Anode connected to negative probe, cathode to positive probe \(\implies\) high resistance / blocks current \(\implies\) meter reads 'OL'.


Why other options are incorrect:

  • Option B: Reading zero in both directions indicates a damaged, short-circuited diode.
  • Option C: Reading 'OL' in both directions indicates a damaged, open-circuited diode.
  • Option D: Reverses the physical forward and reverse conduction characteristics.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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