LED Intensity vs. Voltage – Rankers Physics

Photoelectric Effects and deBroglie Equation: Practice Problem & Solution

Assertion (A): As we increase applied voltage on LED intensity of emitted light first increases then decreases. Reason (R): We use LED in forward bias.  
Both (A) & (R) are true and the (R) is the correct explanation of the (A)
Both (A) & (R) are true but the (R) is not the correct explanation of the (A)
(A) is true but (R) is false
Both (A) and (R) are false

Solution Explained:

To solve this problem, we apply the core principles of Photoelectric Effects and deBroglie Equation. Understanding the underlying formula is key to arriving at the correct answer below:

Assertion (A) is true in a nuanced sense; while intensity generally increases with voltage/current, at very high currents, efficiency can decrease due to thermal effects or Auger recombination (LED droop), leading to a peak and subsequent decrease in intensity. Reason (R) is true; LEDs are operated in forward bias. However, (R) does not explain the intensity variation described in (A).

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