Problem 3.391

A beam of non-relativistic charged particles moves without deviation through the region of space $A$ (Fig. 3.103 ) where there are transverse mutually perpendicular electric and magnetic fields with strength $E$ and induction $B$. When the magnetic field is switched off, the trace of the beam on the screen $S$ shifts by $\Delta x .$ Knowing the distances $a$ and $b,$ find the specific charge $q / m$ of the particles.