[填空题]
A water droplet of radius 0.018 cgszn c))t1bi x53s o)mm remains statioo1-+ouovpl q ;ub.pk:i8 bes6 nary in the air. If the downward-directed electricuq-vbo sobl pei ;1oupk8+ 6:. field of the Earth is $150\,N/C$ how many excess electron charges must the water droplet have? $ \times10^{ 6}$ electrons
