An electron gun with its collector at a potential of $100 \;V$ fires out electrons in a spherical bulb 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 electrons in a circular orbit of radius $12\; cm$. Find e/m of the electron.

Question

$\begin {array} {1 1} (a)\;0.173 \times 10^8C \ kg & \quad (b)\;1.73 \times 10^{11}C \ kg \\ (c)\;17.3 \times 10^{11}C \ kg & \quad (d)\;17.3 \times 10^8C \ kg \end {array}$