Answer:

Explanation:
For a drop in equilibrium, the weight is equal to the electric force (in magnitude):

where here we have
is the weight of the drop
is the magnitude of the electric force, which can be rewritten as

where
q is the charge of the oil drop
is the magnitude of the electric field
Substituting into the equation and solving for q, we find the charge of the oil drop:

Answer:
The metric system was originally devised so that water would have a density of 1 g/cm3, equivalent to 103 kg/m3.