Answer :
Answer:
400nm
Explanation:
Energy of a photon is inversely proportional to it's wavelength
[tex]E\propto \frac{1}{\lambda}[/tex] -(1)
Since the energy of the absorbed photon ([tex]E_a[/tex]) is equal to the sum of energies emitted ([tex]E_1+E_2[/tex])
[tex]E_a=E_1+E_2[/tex]
Using the relation of [tex]E[/tex] and [tex]\lambda[/tex],
[tex]\frac{1}{\lambda_a}=\frac{1}{\lambda_1}+\frac{1}{\lambda_2}[/tex]
[tex]\frac{1}{\lambda_a}=\frac{1}{600\times 10^-^9}+\frac{1}{1200\times 10^-^9}[/tex]
[tex]\lambda_a=400\text{nm}[/tex]