In a Millikan oil drop experiment using a setup like that in
Figure 28.6(b), a 500 V potential difference is applied to plates
separated by 2.00 cm.
Figure 28.6(b)

(a) What is the mass of an oil drop having two extra electrons
that is suspended motionless by the field between the plates?
Answer: ____ kg

(b) What is the diameter of the drop, assuming it is a sphere
with the density of olive oil?
Answer: ____ m