Hydrogen atom is bombarded with electrons accelerated through a potential difference of V, which causes excitation of hydrogen atoms. If the…

Hydrogen atom is bombarded with electrons accelerated through a potential difference of $\displaystyle V$, which causes excitation of hydrogen atoms. If the experiment is being performed at $\displaystyle \mathrm{T}=0 \mathrm{~K}$, the minimum potential difference needed to observe any Balmer series lines in the emission spectra will be $\displaystyle \frac{\alpha}{10} \mathrm{~V}$, where $\displaystyle \alpha=$ $\displaystyle \_\_\_\_$.