Question

If the energy gap of a semiconductor used for the fabrication of an LED is nearly 1.9 eV, then the color of the light emitted by the LED is

• A. White
• B. Red
• C. Green
• D. Blue

Hint:

For LED color problems, remember that energy and wavelength are inversely proportional. Higher energy gaps (like for blue or violet LEDs) correspond to shorter wavelengths, while lower energy gaps (like for red or infrared LEDs) correspond to longer wavelengths.

Answer 1

The Correct Option is B

Step 1: Relation between Energy and Wavelength: The wavelength of light emitted is given by: \[ \lambda = \frac{hc}{E_g} \] Or using the shortcut: \[ \lambda (\text{nm}) \approx \frac{1240}{E_g (\text{eV})} \]
Step 2: Calculation: Given \( E_g = 1.9 \, \text{eV} \). \[ \lambda \approx \frac{1240}{1.9} \approx 652 \, \text{nm} \]
Step 3: Identify the Color: The visible spectrum ranges roughly from 400 nm (Violet) to 700 nm (Red). - Red: \(\sim 620-750\) nm - Green: \(\sim 495-570\) nm - Blue: \(\sim 450-495\) nm Since 652 nm falls in the red region, the LED emits red light.