Concept:Because the forward I-V characteristic is exponential, the slope (conductance \( g_d \)) increases with current, meaning dynamic resistance \( r_d = 1/g_d \) is inversely proportional to forward current.
Formula:$$r_d = \frac{\eta V_T}{I_F} \propto \frac{1}{I_F}$$
Solution:- At \( I_F = 1\text{ mA} \), \( r_d \approx \frac{26\text{ mV}}{1\text{ mA}} = 26\ \Omega \).
- At \( I_F = 100\text{ mA} \), \( r_d \approx \frac{26\text{ mV}}{100\text{ mA}} = 0.26\ \Omega \) (plus contact/bulk resistance).
- Therefore, dynamic resistance decreases inversely as forward current increases.
Why other options are incorrect:- Option A: Dynamic resistance decreases with current; it does not increase.
- Option B: Constant resistance is characteristic of linear ohmic resistors, not non-linear diodes.
- Option C: Dynamic resistance is inversely related to \( I_F \), not proportional to \( I_F^2 \).
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