Intensity of the Signal:

The intensity of a signal depends on the population of the energy level from within that the transition is originating and the prospect of such a transition. According to the Boltzmann statistical distribution, the population of the ground state that is the number of species in the ground state is highest and it keeps on decreasing as we go to higher energy levels. Within case of the atoms the population of any excited state associative to that of the ground state is given through the following formula.

N*/N₀ =g*/g₀e^-ΔE/kT

Or N* =N₀ (g*/g₀)e^-ΔE/kT

Where,

N* and N₀ = Number of atoms in excited state and ground state, correspondingly,

ΔE = Energy difference among ground and excited state (in J),

g* and g₀ = Statistical factors which depend on the degeneracies of the levels involved,

k = Boltzmann constant (= 1.28 × 10^-23 J k^-1), and

T = Absolute temperature.

According to Eq, after the ground state, a lowest energy excited state will be most populated and the population of the higher excited states would decrease progressively. Eq. could be used to determine the population of an excited state along with respect to the ground state.