[Korokian]

wow, this was a problem from my homework i can't figure it out

A chemist on another planet performed the Milikan oil-drop experiment and measured the following charges on in his planet’s unit for charge, the grok: 3.62 x 10-15 groks; 5.93 x 10-15; 9.05 x 10-15 groks. What is the electron’s charge in groks? What is the conversion factor between coulombs and groks?

[Borek]

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[Donaldson Tan]

Please read Forum Rules.

See Clause 4 under Red Violations.

[Korokian]

to be completely honest, i have no idea. 
i'm thinking divide the 3 groks by a common factor and that would be the factor of one grok but i can't find it . and then when you get the charge of a grok you can convert it into coulombs by using dimensional analysis

[Donaldson Tan]

You are to determine the elementary charge (charge of an electron) from the grok data, then equate it to the charge of an electron in columbs.

[Borek]

Korokian: all charges are (more or less) multiples of one value. Find this value.

[Korokian]

borek: i don't know what the value is thats why i need all of your help.  i tried to find the value for about half and hour and gave up ... oh well i handed in my homework already but just out of curiosity you guys can figure it out if you want

[Borek]

borek: i don't know what the value is thats why i need all of your help.  i tried to find the value for about half and hour and gave up ... oh well i handed in my homework already but just out of curiosity you guys can figure it out if you want

Don't forget that values given are experimental results, so they are not exact, but modified by random errors. Divide second and third value by the first one.

[Korokian]

i got 2.5 and 1.63 where do i go from there?

[Borek]

i got 2.5 and 1.63 where do i go from there?

Hmmm, at first sight ratio looked better... These values are not the best starting point.

No idea how to point you in the right direction, so I will just tell you what I did. Look at these numbers rounded down. There are 3.6, 6.0 and 9.0. 3.6 is slightly too large, but both 6 and 9 are multiplies of 3. That suggests that correct value is about 3 and oil drops had the charge of 1 electron, 2 electrons and 3 electrons respectively. Using this assumption you have to calculate average charge of electron (in groks).

3.6, 6.0 and 9.0 can be also - much more precisely - multiplies of 0.6 (times 6, 10 and 15). But I doubt these values are correct, as trick is to select oil droplets with as small charge as possible, 15 is a huge number.

[Korokian]

hmmm wow i never thought of rounding down it would be so much easier, so i guess an estimated answer is the best thing to do .. but yeah this problem is hard lol .

[Korokian]

borek, i got it.
divide all 3 groks by 3.62, you get 1,1.64, and 2.5
then multiply by 2 so its 2, 3.3, and 5
then multiply by 3 so its 6, 10, and 15
then divide 3.62/6 electrons, 5.93/10, 9.05/15
you get the approximate charge of one grok to be 6.00 x10^-16 groks

[Borek]

then divide 3.62/6 electrons, 5.93/10, 9.05/15

IMHO you should assume 3.62 is close to 1 electron, 5.93 to two electrons and 9.05 to three electrons.  6, 10 & 15 are just too large numbers for this experiment.

you get the approximate charge of one grok to be 6.00 x10^-16 groks

If you measure groks in groks you should have 1 as a result

[Korokian]

no, its like using an empircal formula what you said is not precise
i didnt measure groks in groks
i divided the three beginning charges by the number of electrons : 6, 10, and 15 

[Borek]

no, its like using an empircal formula what you said is not precise

Experimental data are never absolutely precise, they are always more or less inaccurate. You have to use not only numbers, but also knowledge about the experiment.

i didnt measure groks in groks

Perhaps it was a mistake, but these are your words: charge of a grok is 6x10^-16 groks. That's measuring groks in groks

i divided the three beginning charges by the number of electrons : 6, 10, and 15

Why do you assume there were 6/10/15 electrons? Becasue these numbers fit data with higher precision? As I already wrote - in the Millikan experiment droplets selected for measurements were those with as small charge as possible. This means several electrons at most, not 15. Thus I suppose the real charges of the droplets to be 1, 2 and 3 electrons - even if it gives larger error. 2, 3 and 5 also look reasonable. IMHO having such experimental results you can't give definite answer about the electron charge, but that's another story.

Note, that going for large numbers of electrons you may find results that will look accurate, but it will be just accidental. Going to the extreme - 362, 593 and 905 electrons (each one with the charge 10^-17 groks) fit data perfectly.