Milikan drop experiment questions

[SaintJude]

Could someone please offer some insight into the Millikan experiment by answering the following questions?

1.What are the most important assumptions of the Millikan experiment?
2. What will happen to a beam of neutrons passing through an E field?
3. How do you explain an atypical value of q (a value not of a multiple of e- charge)?

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[Ssina]

Could someone please offer some insight into the Millikan experiment by answering the following questions?

1.What are the most important assumptions of the Millikan experiment?

as implied by the third question, that the particles are singly ionized
Edit: also that no air resistance most likely... since that would change the results, and for MCAT we don't usually take that into account unless they give us some crazy formula.

2. What will happen to a beam of neutrons passing through an E field?

since not charged, then no force from the electric field, so nothing.. just falls through the apparatus.

3. How do you explain an atypical value of q (a value not of a multiple of e- charge)?

idk what besides errors in reading/calculations (like measuring the mass of the particle) can account for it, since the charge is quantized

nevertheless, good questions, requires more info that I know... so just guessing here
sure someone else can elaborate extensively

 

[MedPR]

I agree, good questions. Makes me realize that I don't know the experiment as well as I thought.

Could someone please offer some insight into the Millikan experiment by answering the following questions?

1.What are the most important assumptions of the Millikan experiment?
2. What will happen to a beam of neutrons passing through an E field?
3. How do you explain an atypical value of q (a value not of a multiple of e- charge)?

1. The experiment demonstrated that electric charge is quantized, that is, always in multiples of the charge of an electron. And of course, it determined that the charge of an electron is 1.6E-19. I'm not sure of the assumptions made during the experiment though, and I think that's what you are asking. Sorry.

2. Nothing, the neutrons wouldn't "feel" any attractive force so they would pass right on through assuming no other forces besides electromagnetic.

3. If you mean during the experiment, I think the charge wouldn't have been measured to be exactly 1.6E-19 if the electron didn't penetrate and settle in the exact center of mass of the drop. Not really sure otherwise though.

 

[BerkReviewTeach]

1. What are the most important assumptions of the Millikan experiment?

(a) You assume that the only two forces acting on the suspended oil drop are gravitational pull downward and the electrostatic force. That's a reasonable one.
(b) You also assume that all oil drops are equally massive (identical in size), which cannot be true. There's no way to isolate the oil drop in the apparatus, so we make the assumption that all oil drops are equal in size to some average oil drop.

2. What will happen to a beam of neutrons passing through an E field?

As both previous posters have already pointed out, nothing. If q = 0, then qE = 0.

3. How do you explain an atypical value of q (a value not of a multiple of e- charge)?

In different trials, the mass of the suspended oil drop may be slightly different, which would require a slightly different E field to keep it suspended. We don't know the exact value for the mass of the oil drop in the experiment, so we use an average value in our calculations. In our calculation where qE = mg, the E varies from trial to trial. Although the m also varies from trial to trial as well, we don't know how, so we must plug in a fixed value for m and solve for a value for q that varies from trial to trial. The thought is that if you do enough trials, the average value for q will fall out of the data.

 

[SaintJude]

Thank you! Thank you!

 

[dranet]

The other important assumption is that the force opposing that of the Electric Field is that associated with gravity.