[填空题]
In a photocell, ultraviolet tbi m9u)f 9 kms 6i+hi:1u/a5t4ui hyl(Uzkf b+qc5-/z eV) light provides enough energy to some electrons in barium metal to eject them from a surface at high speed. See Fig. 17–33. To measure the maximum energy of the electrons, another plate above the barium surface is kept at a negative enough potential that the emittz-k5/zcf bq+eed electrons are slowed down and stopped, and return to the barium surface. If the plate voltage is $-3.02V$ (compared to the barium) when the fastest electrons are stopped, what was the speed of these electrons when they were emitted? $ \times10^{6 }\,m/s$
