Question

LED is constructed from $Ga-As-P$ semiconducting material. The energy gap of this LED is $1.9\text{eV}$. Calculate the wavelength of light emitted and its colour.
$[h=6.63\times {10}^{34}\text{J s}\text{and}c=3\times {10}^8{\text{ms}}^{-1}]$

• A. $654\text{nm}$ and red colour
• B. $1046\text{nm}$ and blue colour
• C. $1046\text{nm}$ and red colour
• D. $654\text{nm}$ and orange colour

Answer 1

The correct option is A $654\text{nm}$ and red colour

We know that $E=\frac{hc}{\lambda }$

$\lambda =\frac{hc}{E}\Rightarrow \lambda \left(\text{in nm}\right)=\frac{1240}{E\left(\text{in eV}\right)}$

$\lambda =\frac{1240}{1.9}=652.63\text{nm}=654\text{nm}$

Wavelength of red light is $620\text{nm}$ to $750\text{nm}$

So, option (a) is the correct answer .