What is the Charge on a Suspended Oil Drop in Millikan's Experiment?

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SUMMARY

The discussion centers on Robert Millikan's experiment to determine the charge of an electron using suspended oil drops. The key parameters include a potential difference creating an electric field of 10,000 N/C and an oil drop mass of 3.27 x 10^-16 kg. The charge on the drop is calculated using the equation qE = mg, leading to a charge magnitude of approximately 3.2 x 10^-19 C. Participants emphasize understanding the balance of electric force and gravitational force acting on the oil drop.

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  • Study the derivation of the equation qE = mg in the context of electric forces
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Homework Statement


Robert Millikan received a Nobel Prize for determining the charge on the electron. To do this he set up a potential difference between two horizontal parallel metal plates. He then sprayed a drops of oil between the plates and adjusted the potential difference until drops of a certain size remained suspended at rest between the plates. Suppose that when the potential difference between the plates is adjusted until the electric field is 10,000 N/C downward, a certain drop with a mass of 3.27 x 10^-16 kg remains suspended. what is the magnitude of the charge on this drop?

Homework Equations


umm... i suppose E = Kc x (q/r^2) and f = Kc x (q1)(q2)/r^2 would apply. I'm not sure if i need anything else though.

The Attempt at a Solution



i have got the right answer i think, but i have no idea how what is going on.

(3.27 x 10^-16)(9.8) = 3.2046 x 10^-15 = qE
E = 3.2 x 10^-19

i understand that here, mass is being multiplied by free fall acceleration, and then set equal to charge x electric field, but i don't know where this came from. does it have anything to do with the unit of electric force being Newtons, or kg x m/s^2. some explanation would be greatly appreciated.
 
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Draw a free body diagram of the oil drop and work out the conditions for it to remain suspended.
 
yeah thanks. i figured it out minutes after. it's basically just electric field against gravity. thank you.
 

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