Question

6) The adjacent graph shows the current-voltage characteristics for a Light Emitting Diode. a. Estimate the wavelength of the light it produces. b. Estimate the energy per photon in eV. Red LED 1.8 1.6 14 1.2 y=5.9228x + 1.6872 0.8 0.6 0.4 0.2 0.01 0.02 0.03 Current (A)

Answer 1

Ans: From the graph, the threshold voltage for the given LED is , Vo = 1.6872 V

We know for an LED,

                                         Band Gap = Eg = eVo = hf = hc/$\lambda$

a) So, We got

                                                  $\lambda=\frac{hc}{eV_{o}}$

                                   

6.626 1043 10 1.602 10-19 1.6872

          =>The wavelength of the light produced $\large \lambda =734.85 \ nm$

b)   E = e Vo = e x 1.6872 V$\large \lambda =734.85\ nm$

= 1.6872 eV

             The energy per photon is 1.6872 eV.