Answer:
[tex]4.8\cdot 10^{-19} C[/tex]
Explanation:
For a drop in equilibrium, the weight is equal to the electric force (in magnitude):
[tex]W = F_e[/tex]
where here we have
[tex]W=1.00\cdot 10^{-14}N[/tex] is the weight of the drop
[tex]F_e[/tex] is the magnitude of the electric force, which can be rewritten as
[tex]F_e = qE[/tex]
where
q is the charge of the oil drop
[tex]E=2.08 \cdot 10^4 N/C[/tex] is the magnitude of the electric field
Substituting into the equation and solving for q, we find the charge of the oil drop:
[tex]q=\frac{W}{F_e}=\frac{1.00\cdot 10^{-14}N}{2.08\cdot 10^4 N/C}=4.8\cdot 10^{-19} C[/tex]