An oil drop (m = 1.6 x 10-16 kg) is suspended between plates separated by 1.8 cm. The voltage across the plates is 125 V. Is this possible?

E = V / d       125 V / .018 m = 6940 V/m     electric field

F = E Q       force on Q due to E

F = E n e     where n is the number of electrons in Q

m g = E n e

n = m g / E e     where n is the number of electrons e needed to support drop

n = 1.6 * 10E-16 * 9.8 / (6940 * 1.6 * 10E-19)

n = 1.41

Since n needs to be an integral number of charges, the drop would

not be suspended (motionless under these conditions).

i think it would be 5