# Millikan's Experiment- Oil drop containing an even number of charges

What error could occur if only a few oil drops were used, or if all the oil drops contained an even number of charges?

• -1 What do you think? We expect you to show the results of your own thinking, and to explain what difficulty you are having with the question. – sammy gerbil Dec 21 '17 at 2:35

## 1 Answer

If all the drops contained an even number of electrons (e.g. 2,6,22, and 100), you might look at the charges you measured and determine that the fundamental unit of charge was $2e$ (rather than $e$ which would be the correct answer).

If you only did a few drops, you might have bad luck and get ones that are all divisible by numbers larger than $e$. (maybe you got charges of roughly $7e$, $49e$, and $98e$, all of which are divisible by $7e$).

• I did the experiment back in 1966, and can only vaguely recall how it went. But I don't think I got charges larger than maybe 5e, and got several of 1e (out of maybe 10 total runs). – Hot Licks Dec 21 '17 at 1:26
• I just did it a couple days ago for a class I'm preparing to teach for, and seeing drops up to $~25e$ was not uncommon. Depends on the oil used and the sprayer. (I may have been exaggerating with 98 though!) – Bunji Dec 21 '17 at 5:14