Transitions between three energy levels in a particular atom give rise to three spectral lines of wavelengths, in increasing magnitudes, ${\mathrm{\lambda }}_1, {\mathrm{\lambda }}_2 \mathrm{and} {\mathrm{\lambda }}_3$. Which one of the following equations correctly relates ${\mathrm{\lambda }}_1, {\mathrm{\lambda }}_2 \mathrm{and} {\mathrm{\lambda }}_3$?

• A

  ${\mathrm{\lambda }}_1= {\mathrm{\lambda }}_2-{\mathrm{\lambda }}_3$

• B

  ${\mathrm{\lambda }}_1= {\mathrm{\lambda }}_3-{\mathrm{\lambda }}_2$

• C

  $\frac{1}{{\mathrm{\lambda }}_1}= \frac{1}{{\mathrm{\lambda }}_2}+\frac{1}{{\mathrm{\lambda }}_3}$

• D

  $\frac{1}{{\mathrm{\lambda }}_1}= \frac{1}{{\mathrm{\lambda }}_3}+\frac{1}{{\mathrm{\lambda }}_2}$