# A monoenergetic electron beam with speed of $5.2 \times 10^6\: m/s$ is subjected to a magnetic field of $1.3 \times 10^{-4}T$ normal to the beam velocity. What is the radius of the circle traced by the beam, given $\large\frac{e}{m}$ for electron equals $1.76 \times 10^{11}C /kg$?
$\begin {array} {1 1} (a)\;22.7\: m & \quad (b)\;2.27\: cm \\ (c)\;22.7\: cm & \quad (d)\;2.27\: m \end {array}$