1.

A 12.5 eV electron beam is used to bombard gaseous hydrogen at room temperature. What series of wavelengths will be emitted?

Answer»

The first, second and third excited energies for hydrogen atom are
E’1 = E2 – E1 = -3.4 – [-13.6] = 10.2 eV,
E’2 = E3 – E1 = -1.51 – [-13.6] = 12.09 eV,
and E’3 = E4 – E1 = -0.85 – [-13.6] = 12.75 eV
It follows that when a 12.5 eV electron beam is used to bombard gaseous hydrogen at room temperature, the H – atoms at the most will be raised to n = 3 level. The H – atoms may come to ground state directly or via n = 2 level. Therefore, the wavelengths emitted will lie in Balmer series [for de-excitation from n = 3 level to n = 2 and 1 level] and Lyman series [for de­excitation from n = 2 level to n = 1 level].


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