= Electrostatic deflection by finite parallel plates
{title2=$x=V_d\ell D/(2dU_a)$}
An <electron> accelerated through <voltage> $U_a$ crosses deflecting plates of length $\ell$ and separation $d$. If their <electric field> is uniform and their centre is distance $D$ from a screen, constant transverse <acceleration> inside the plates followed by free drift gives the displayed screen displacement. It includes the displacement accumulated inside the plates. The plate-exit displacement is $x\ell/(2D)$, which must be smaller than the half-gap for a centrally injected beam to pass.
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