[填空题]
In a television picture tube, elect n-v 5qsql;s; s r1clne7ls63n rt7+bzrons ar/2 (:)m xhsc i.jedqize accelerated by thousands of volts through a vacuum. If a television set were l.2d (mjzqhi csx /i:)eaid on its back, would electrons be able to move upward against the force of gravity? What potential difference, acting over a distance of 3.0 cm, would be needed to balance the downward force of gravity so that an electron would remain stationary? Assume that the electric field is uniform. $ \times10^{ -12}\,V$
