Physics Electronics PMDC Conceptual Practice
PMDC Verified Question 195 of 494
When inspecting a discrete through-hole Light Emitting Diode (LED), how can the positive terminal (anode) be physically identified before connecting it into a circuit?
A
It has the longer metallic lead and is adjacent to the rounded edge of the plastic casing
B
It has the shorter metallic lead and is adjacent to the flat notch on the casing
C
It is internally attached to the larger anvil-shaped electrode
D
Its lead is coated with a red insulating stripe
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 has the longer metallic lead and is adjacent to the rounded edge of the plastic casing
Concept:

Discrete LEDs use standardized physical packaging cues to distinguish the anode (positive) from the cathode (negative).

Formula:

$$\text{Anode } (+) \longleftrightarrow \text{Longer Lead / Rounded Rim}, \quad \text{Cathode } (-) \longleftrightarrow \text{Shorter Lead / Flat Notch}$$

Solution:

  • The longer terminal lead corresponds to the anode (P-region, positive).


  • The shorter terminal lead corresponds to the cathode (N-region, negative), which is also marked by a flat notch on the rim of the plastic casing.


Why other options are incorrect:

  • Option B: The shorter lead and flat notch identify the cathode, not the anode.
  • Option C: The larger internal anvil electrode is the cathode; the smaller post electrode is the anode.
  • Option D: Standard LED leads are uninsulated tinned copper without colored stripes.

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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