# Millikan oil drop experiment charge determination

• Jacob Pilawa
In summary, the conversation discusses a physics problem involving a charged oil droplet suspended between two parallel plates at different voltages. The table of voltage values is given and the task is to determine the charge on the droplet in one of the cases. A hint is given to find integer values that satisfy the given equations. After some discussion, the solution of 7e=1.12x10^-18 coulumbs is determined, with the other three integers being 7, 6, and 5. The calculations were almost exact and the participants were ecstatic to have solved the problem.
Jacob Pilawa
Howdy y'all!

If you could help with the following question, my physics class and I would be extremely grateful.

A charged oil droplet is suspended motionless between two parallel plates (d=0.01m) that are held at a potential difference V. Periodically, the charge on the droplet changes as in the original oil drop experiment. Each time the charge changes, V is adjusted so that the droplet remains motionless. Here is a table of recorded values of the voltage:

i. 350 V

ii. 408.3 V

iii. 490 V

iv. 612.5 V

From the data above, determine the charge on the dorplet for case (i) above. What assumptions do you need to make? (Hint: the ratio of voltages = ?)

Thanks a ton, we've been stumped.

I'm going to be honest here, me and 2 friends have been working on this for about 4 hours, and we don't really have any substantial work to show. Any help would be great. Thanks.

I can give you a hint, but I haven't solved it myself yet: ## 350* \, Q_1=408.3* \, Q_2=490* \, Q_3=612.5* \, Q_4 ##. ## Q_4<Q_3<Q_2<Q_1 ##. Find some ## Q_o ## so that ## Q_4=n_4 \, Q_o ##, ## Q_3=n_3 \, Q_o ##, etc., ## n_4, n_3,... ## integers (hopefully small ones). Sorry, I edited a couple of times because I read it incorrectly.

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I can give you a hint, but I haven't solved it myself yet: ## 350 \, Q_1=408.3 \, Q2=490 \, Q_3=612.5 Q_4 ##. ## Q_4<Q_3<Q_2<Q_1 ##. Find some ## Q_o ## so that ## Q_4=n_4 \, Q_o ##, ## Q_3=n_3 \, Q_o ##, etc., ## n_4, n_3,... ## integers (hopefully small ones).
Okay, this makes sense. However, where can we go from here? Is there anyway to solve for the integers?

I have it, but I'm not allowed to give the solution. I can give you a hint though. The smallest number, ## Q_4 ## is greater than 3. Another hint is the numbers are exact enough, that I think the data is probably simply constructed by the professor as a good learning exercise. One additional hint=let ## Q_4=n_4 ## (Ignore the ## Q_o ## part mentioned previously.) Please let us know if you figured out the answer.

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I have it, but I'm not allowed to give the solution. I can give you a hint though. The smallest number, ## Q_4 ## is greater than 3.

Okay, so we talked it out a little bit. So does this mean that the answer is 7e=1.12x10^-18 coulumbs?

Jacob Pilawa said:
Okay, so we talked it out a little bit. So does this mean that the answer is 7e=1.12x10^-18 coulumbs?
Yes. One additional question for you=what did you get for the other 3 integers? And were the calculations almost exact?

Yes. One additional question for you=what did you get for the other 3 integers?

We got all the integers as 7,6,5, and 4. Thank you so much! We just screamed in excitement and relief.

## 1. What is the Millikan oil drop experiment?

The Millikan oil drop experiment is a famous physics experiment conducted in 1909 by Robert Millikan to determine the charge of an electron. It involved observing and measuring the motion of tiny oil droplets in an electric field.

## 2. How did Millikan determine the charge of an electron?

Millikan used the oil drop experiment to measure the charge of an electron by balancing the gravitational force and the electric force acting on the oil droplets. He then calculated the charge using the known values of the electric field and the viscosity of air.

## 3. What is the significance of the Millikan oil drop experiment?

The Millikan oil drop experiment is significant because it provided the first direct measurement of the charge of an electron, which was a constant value independent of the material and size of the oil droplets. This experiment also helped confirm the atomic structure of matter and the existence of indivisible particles like electrons.

## 4. Were there any limitations or controversies surrounding the Millikan oil drop experiment?

There were some controversies surrounding the Millikan oil drop experiment, particularly regarding the accuracy of Millikan's data and the possibility of systematic errors. However, subsequent experiments and advancements in technology have confirmed the validity of Millikan's findings.

## 5. How did the Millikan oil drop experiment contribute to the development of modern physics?

The Millikan oil drop experiment was a crucial step in the development of modern physics as it provided evidence for the quantization of electric charge and helped establish the concept of the electron as a fundamental particle. It also paved the way for further research in the field of subatomic particles and their properties.

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