Atoms & Nuclei

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47 of 239

Question 47 of 239

A 12.5eV12.5eV electron beam is used to bombard gaseous hydrogen at room temperature. The number of spectral lines emitted will be:

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Answer: (D) 33

According to Bohr's postulates, if an electron absorbs a photon with energy equal to the difference between the energies of an excited state and the ground state, it will jump to a higher energy orbital.
Considering that the energy of the colliding electron is 10.2eV10.2eV or 12.09eV12.09eV, depending on how much energy is lost during the collision. n=3n=3 is the maximum excited state. Hence, there are spectral lines in a total of
C23=3!2!1!=3\begin{matrix}C23 & = & \dfrac{3!}{2!1!} \\ & = & 3\end{matrix}

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