Question

The frequency of radiation absorbed or emitted when transition occurs between two stationary states that differ in energy by:$\Delta E$, is given by:
$v=\frac{\Delta E}{h}=\frac{E_2-E_1}{h}$Where $E_1$ and $E_2$ are the energies of the lower and higher allowed energy states respectively. This expression is?

Answer 1

According to bohr when an atom makes a transition from one energy level to a lower level it emits a photon with energy equal to the energy difference between initial and final levels. If $E_1$ is the initial energy of the atom before such a transition, $E_2$ is it's final energy after the transition, and the photons energy is $hf=\frac{hc}{\lambda }$, then conservation of energy gives, $E_1-E_2=\frac{hc}{\lambda }$.