Question:

Which of the following statements is true?

Updated On: Sep 3, 2024
  • The wavelength of light emitted by LED depends on the applied voltage across the LED.
  • LED emits light when it is reverse biased
  • The V-I characteristics of an LED is similar to that of a silicon p-n junction diode
  • LED is made of a thin layer of lightly doped semiconductor material
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The Correct Option is D

Solution and Explanation

Let's examine each statement:
1. The wavelength of light emitted by LED depends on the applied voltage across the LED. - This statement is true to a certain extent. The color (or wavelength) of the light emitted by an LED is primarily determined by the energy bandgap of the semiconducting material it's made from. However, there can be slight variations in the emitted wavelength based on the current (which is related to the applied voltage) through the LED. At high current levels, the wavelength can shift slightly. But in common usage, the color of an LED is generally determined by its material, not the voltage applied. 
2. LED emits light when it is reverse biased.- This statement is false. LEDs emit light when they are forward biased. In reverse bias, they don't emit light and can get damaged if the reverse voltage exceeds the breakdown voltage. 
3. The V-I characteristics of an LED is similar to that of a silicon p-n junction diode.- This statement is not completely accurate. While both LED and a silicon p-n junction diode show a knee voltage and begin conducting in forward bias, an LED starts emitting light after its threshold voltage. Furthermore, the "knee" or threshold voltage for an LED is typically higher than that for a silicon diode. 
4. LED is made of a thin layer of lightly doped semiconductor material. - This statement is not entirely accurate. An LED is made from a p-n junction of semiconducting materials. The doping levels can vary, but to say it's just a "thin layer of lightly doped semiconductor material" oversimplifies the structure. 
Of the given options, the closest to being accurate is the first statement, but it's not completely true without qualifications. So, strictly speaking: None of the given statements are unequivocally true without reservations.
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