Explanation:
From figure,
\(\frac{{hc}}{\lambda } = 3E - E = 2E\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(1)\)
\(\frac{{{\rm{hc}}}}{{{\lambda ^1}}} = \frac{{5E}}{3} - E = \frac{2}{3}E\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,(2)\)
Divide (1) by (2), we get
\(\frac{{\lambda '}}{\lambda } = 3\,\) or \(\lambda ' = 3\lambda \,\)
