Answer:[tex]\lambda _3=\frac{\lambda }{3}[/tex]
Explanation:
Given
[tex]E_3-E_2=\frac{hc}{\lambda }[/tex]
also [tex]E_2-E_1=2\left ( E_3-E_2\right )[/tex]
Let wavelength produce during transition from 2 to 1 is [tex]\lambda_0[/tex]
[tex]\frac{hc}{\lambda _0}=2\frac{hc}{\lambda }[/tex]
[tex]\lambda _0=\frac{\lambda }{2}[/tex]
For [tex]E_3 to E_1 transition [/tex]
[tex]E_3-E_1=E_3-E_2+E_2-E_1[/tex]
[tex]E_3-E_1=\frac{hc}{\lambda }+2\frac{hc}{\lambda }[/tex]
[tex]\frac{hc}{\lambda _3}=3\frac{hc}{\lambda }[/tex]
[tex]\lambda _3=\frac{\lambda }{3}[/tex]