Physics Electronics PMDC Conceptual Practice
PMDC Verified Question 275 of 494
A forward-biased ideal silicon PN junction diode carries a steady forward current of \( I_F = 26.0\text{ mA} \) at room temperature (\( V_T = 26.0\text{ mV} \)). Assuming an ideality factor of \( \eta = 1.0 \), what is its dynamic (AC) resistance \( r_d \)?
A
26.0 Ω
B
0.10 Ω
C
1.00 Ω
D
10.0 Ω
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: 1.00 Ω
Concept:

The dynamic (AC) resistance of a conducting diode is given by \( r_d = \frac{\eta V_T}{I_F} \).

Formula:

$$r_d = \frac{\eta V_T}{I_F}$$

Solution:

  • Given: \( \eta = 1.0 \), \( V_T = 26.0\text{ mV} = 0.026\text{ V} \), and \( I_F = 26.0\text{ mA} = 0.026\text{ A} \).


  • Dynamic resistance: \( r_d = \frac{0.026\text{ V}}{0.026\text{ A}} = 1.00\ \Omega \).


Why other options are incorrect:

  • Option A: 26.0 Ω would be the dynamic resistance at \( I_F = 1.0\text{ mA} \).
  • Option B: 0.10 Ω corresponds to a forward current of 260 mA.
  • Option D: 10.0 Ω corresponds to a forward current of 2.6 mA.

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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