If the electrons that lose energy to a mercury atom continue to accelerate, they can acquire enough kinetic energy to excite another atom, leading to a drop in current. At what voltage does the drop in current begin? If the electrons that lose energy to a mercury atom continue to accelerate, they can acquire enough kinetic energy to excite another atom, leading to a drop in current. At what voltage does the drop in current begin? 7.4 V 4.9 V 9.8 V 14.7 V