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Solution


Q.

A 12.5 eV electron beam is used to bombard gaseous hydrogen at room temperature. The number of spectral lines emitted will be             [2023]
1 2  
2 1  
3 3  
4 4  

Ans.

(3)

According to Bohr's postulates, an electron makes jump to higher energy orbital if it absorbs a photon of energy equal to difference between the energies of an excited state and the ground state. Assuming that collided electron takes energy equal to 10.2 eV or 12.09 eV from the incoming electron beam (some part lost due to collision). The maximum excited state is n=3. So, number of spectral lines =3(3-1)2=3