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jekch85
11-20-2006, 09:53 PM
Hi all. I'm new here and I'd appreciate any help I can get!

1) In a trial of Millikan's oil drop experiment, we find that the electric field required to suspend a tiny oil particle with mas s 1.46x10^014 kg is 2.98x10^5 N/C upward. We can infer that the

a) is missing three electrons
b) is missing two electrons
c) has three extra electrons
d) has two extra electrons

I determined that the particle has a charge of 4.8x10^-19 instead of 1.6x10^-14. I just can't figure out if they are missing or extra. I assumed extra, but I think I'm missing something. Any help is very much appreciated!!

OfficeShredder
11-20-2006, 10:50 PM
First, if the electric field points upwards, and the force on the oil drop is upwards (to fight gravity), does that mean the oil drop has a positive or negative charge?

jekch85
11-20-2006, 11:21 PM
Well, the electrons have a negative charge, but I guess the oil droplet would have a positive charge because the electric field has a positive charge. Since the number increases in negative charge, would this mean there are extra electrons pulling it downward?

OfficeShredder
11-21-2006, 12:31 AM
Well, the electrons have a negative charge, but I guess the oil droplet would have a positive charge because the electric field has a positive charge. Since the number increases in negative charge, would this mean there are extra electrons pulling it downward?

Electrons have a negative charge. So if you have a neutral oil droplet, and remove an electron, does the new oil droplet have a positive or negative charge?

I don't understand the second half of your post at all

jekch85
11-21-2006, 12:41 AM
I don't really think I understand it either.

If you remove an electron from the oil droplet, it now has a positive charge. So..that would mean that there are extra electrons, making the oil droplet more positive?

OfficeShredder
11-21-2006, 12:44 AM
I don't understand this idea about removing an electron giving extra electrons. Here's how it works

You have an oil droplet. It has an even number of protons and electrons, say 10 of each. You then remove 2 electrons. It has 8 electrons, and 10 protons, so its electric charge is equivalent to having 2 protons. Where the other 2 electrons went is irrelevant for the problem

jekch85
11-21-2006, 12:47 AM
I don't think it's irrelevant, the question is asking if there are missing or extra electrons. What I am trying to figure out is which one it is.

OfficeShredder
11-21-2006, 02:30 PM
We already answered the question. The oil drop has a positive charge. Hence, it is missing electrons. If it had extra electrons, it would have a negative charge