An electron gun with its anode at a potential $100\;v$ fires out electrons in a spherical bulls containing hydrogen gas at low pressure $(10^{-2}\;mm\;of\;Hg)$ . A magnetic field of $2.83 \times 10^{-4}\;T$ curves the path of the electron in a circular orbit of radius 12.0 cm (The path can be viewed because the gas ions in the path focus the beam by attracting electrons and emitting light by electron capture. this method is known as "fine beam tube " method. Determine e/m from the data .

Question

$\begin{array}{1 1} 1.73 \times 10^{11} \;Cg^{-1} \\ 1.73 \times 10^{12} \;Cg^{-1} \\ 1.73 \times 10^{11} \;Ckg^{-1} \\ 1.73 \times 10^{11} \;Ckg^{-1}\end{array} $