An LED is constructed from a p-n junction diode using GaAsP. The...

The energy of light of wavelength $\lambda$ is given by $\mathrm{E}=\mathrm{hv}=\frac{\mathrm{hc}}{\lambda} \Rightarrow \lambda=\frac{\mathrm{hc}}{\mathrm{E}}$Here, $\mathrm{h}=$ Planck's constant $=6.63 \times 10^{-34} \mathrm{~J}-\mathrm{s}\mathrm{c}=$ speed of light $=3 \times 10^8 \mathrm{~m} / \mathrm{s}\mathrm{E}=$ energy gap $=1.9 \mathrm{eV}=1.9 \times 1.6 \times 10^{-19} \mathrm{~J}$ Substituting the given values in Eq. (i), we get $$\begin{aligned} \Rightarrow \quad \lambda& =\frac{6.63 \times 10^{-34} \times 3 \times 10^8}{1.9 \times 1.6 \times 10^{-19}}\\ & =6.54 \times10^{-7} \mathrm{~m} \approx654 \mathrm{~nm} \end{aligned}$$Thus, the wavelength of light emitted from LED will be $654 \mathrm{~nm}$.