$A$ rectangular region of dimensions $(\omega \times l)$ where $\omega \ll l$ has a constant magnetic field $B$ directed into the plane of the paper as shown in the figure. On one side,the region is bounded by a screen. On the other side,positive ions of mass $m$ and charge $q$ are accelerated from rest by a parallel plate capacitor at a constant potential difference $V$ and enter the magnetic field region through a small hole. Which one of the following statements is correct regarding the charge $q$ on the ions that hit the screen?

  • A
    Ions with $q > \frac{2mV}{B^2\omega^2}$ will hit the screen
  • B
    Ions with $q < \frac{2mV}{B^2\omega^2}$ will hit the screen
  • C
    All ions will hit the screen
  • D
    Only ions with $q = \frac{2mV}{B^2\omega^2}$ will hit the screen

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