Q.
The electric field strength in NC−1 that is required to just prevent a water drop carrying a charge 1.6×10−19C from falling under gravity is (g=9.8ms−2, mass of water drop = 0.0016g)
Charge on drop =1.6×10−19C
Mass of the drop =0.0016g =16×10−4g =16×10−7kg g=9.8m/s−2
In balance position, mg=qE
where, E is electric field strength. E=qmg=1.6×10−1916×10−7×9.8 =9.8×1013N/C