The only electron in the hydrogen atom resides under ordinary conditions on the first orbit. When energy is supplied, the electron moves to higher energy orbit depending on the amount of energy absorbed. When this electron returns to any of the lower orbits, it emits energy. Lyman series is formed when the electron returns the lowest orbit while Balmer series is formed when the electron returns to the second orbit. Similarly, Paschen, Brackett, and Pfund series are formed when an electron returns to the third, fourth, and fifth from higher orbits, respectively.
A maximum number of lines produced when an electron jumps from nth level to ground level is equal to n(n−1)2.
If the electron comes back from the energy level having energy E2 to the energy level having energy E1, then difference may be expressed in terms of energy of photon as :
E2−E1 = ΔE, λ=hcΔE.
Since h and c are constant, ΔE corresponds to definite energy thus, each transition from one energy level to another will produce a light of definite wavelength. This is actually observed as a line in the spectrum of a hydrogen atom.
Wave number of line is given by the formula :
v = RZ2(1n21−1n22)
Where R is a Rydberg constant.
In a single isolated atom, an electron makes transition from a fifth excited state to second state then maximum number of different types of photons observed is :