# LED is constructed from Ga-As-P semiconducting material. The energy

Question:

LED is constructed from Ga-As-P semiconducting material. The energy

gap of this LED is $1.9 \mathrm{eV}$. Calculate the wavelength of light emitted and its

colour. $\left[\mathrm{h}=6.63 \times 10^{-34} \mathrm{Js}\right.$ and $\left.\mathrm{c}=3 \times 10^{8} \mathrm{~ms}^{-1}\right]$

1. $654 \mathrm{~nm}$ and red colour

2. $1046 \mathrm{~nm}$ and blue colour

3. $1046 \mathrm{~nm}$ and red colour

4. $654 \mathrm{~nm}$ and orange colour

Correct Option: 1

Solution:

(1)

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

$=\frac{h c}{E} \Rightarrow \frac{1240(i n e V)}{E(i n e V)}$

$=\frac{1240}{1.9}$

$=652.63 \mathrm{~nm} \approx 654 \mathrm{~nm}$

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

So, answer is $1 .$