Concept:The dynamic resistance of a diode is proportional to the thermal voltage \( V_T = k T / q \), meaning it varies directly with absolute temperature \( T \) at a constant forward current.
Formula:$$r_d = \frac{\eta V_T}{I_F} = \frac{\eta k T}{q I_F} \implies r_d \propto T$$
Solution:- Because thermal voltage is \( V_T = \frac{k T}{q} \), the dynamic resistance at a fixed current \( I_F \) is \( r_d = \frac{\eta k T}{q I_F} \).
- Therefore, \( r_d \) increases linearly with absolute temperature \( T \).
Why other options are incorrect:- Option A: Dynamic resistance is directly proportional to temperature, not inversely proportional.
- Option C: Dynamic resistance depends on thermal voltage, which is temperature-dependent.
- Option D: The relationship is linear with \( T \), not proportional to \( T^4 \).
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