A mono energetic $(18\;kev)$ electron beam initially in the horizontal direction is subjected to a horizontal magnetic field of $0.4\;G$ normal to the initial direction . Estimate the up or down deflection of the beam over a distance of $30\;cm(m_e=9.11 \times 10^{-19}\;c)$

Question

$\begin{array}{1 1} 4\;mm \\ 4\;cm \\ 4\;m \\ \text{none of the above} \end{array}$