When white radiation is passed through a sample hydrogen gas at room temperature, absorption lines an observed in Lyman series only. Explain.

We know, according to Bohr’s Model, the energy ∆E released, when electrons move from n₂ energy level to n₁ energy level is given by,


At room temperature, all electrons in a hydrogen atom are in ground state. In order to excite them to n=2 level a minimum of 10.2 eV energy is needed. This is because,



White light contains radiations of energy around 10.2eV. So, it excites electrons to n=2 level. During de-excitation, electrons move from n=2 level to n=1 level. This corresponds to the Lyman Series.


Thus, absorption lines are only observed in Lyman Series.


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