Millikan Oil Drop Experiment - Online Tutor, Practice Problems & Exam Prep

The Millikan oil drop experiment, conducted by Robert Millikan and Harvey Fletcher in 1913, was pivotal in determining the fundamental charge of an electron. Utilizing oil droplets, charged plates, gravity, and X-rays, they were able to measure the electric force and suspend a charged oil droplet between two plates. By adjusting the voltage to counteract gravity, the droplet's suspension allowed them to calculate the electron's charge as:

$-1.60\times {10}^{-19}\text{coulombs}$

a critical value for understanding atomic structure. This experiment built upon J.J. Thomson's earlier work, providing a quantitative measure of the electron's negative charge and advancing the field of atomic physics.

Millikan Oil Drop Experiment

Hey everyone. So here we're going to say that in 1897, JJ Thompson's Capital Rate 2 experiments led to discovery of the negative charge of electrons. But what we can say further is that Thompson was unable to determine how much negative charge an electron possesses, and it wasn't until 1913 where Robert Milliken and Harvey Fletcher discovered the fundamental charge of an electron.

Now here we're going to talk about the Milliken oil drop experiment. Here we're going to say that Milliken and Fletcher used oil droplets, charged plates, gravity, and X-rays to determine the amount of charge. And here there are certain things that we need to remember. We have our atomizer. This is just the container used to disperse the individual oil droplets. Here in this drawing we can say that this is our atomizer and what we do here is we would basically drive this atomizer into this opening and basically squeeze on the nozzle and a mist of oil droplets will be sprayed within our apparatus.

Next we need to realize that we have something called electric force. This is basically the attractive and repulsive forces between particles based on electric charges. Remember in chemistry opposite charges attract. We're going to say same charge as repel. Now once we've stuck in this atomizer and basically dispersed our old droplets into the apparatus, Here we have our oil droplets. These little dots. What happens here is these oil droplets are going to fall through. Here, This plate, this plate here on top is our positively charged plate.

OK, now going back to the experiment, the oil droplets we say were introduced to the atomizer. They go through the positive plate here. This is our X-ray source. So it's basically going to ZAP our oil droplets. So the X-ray source zaps our oil droplets to give them a negative charge. Here we have our microscope, which basically looks at our charged oil droplet, which would be this little dot right here. So here that's our charged oil droplet and this blue plate here would just be our negatively charged plate.

Now this box here would be our voltmeter which will read the voltage or charge that could be produced within this experiment. Now here if we turn on the power of the charge plates, it's going to create an electric field. And what's important about this electric field is we're going to say that if the voltage is turned up and it becomes greater than the force of gravity, that the the droplet itself will rise. But if the voltage is not high enough and it's less than the force of gravity, then the old droplet will fall.

What we have to do here is we have to apply the right amount of voltage. That'll help if we can do it. Help the droplet be suspended in air. And if we could suspend that droplet in air between our positive and negative plates, it's through the suspension that we can figure out the charge of our electron. And that's what they were able to do with this experiment. See, through the suspension of the oil droplets, the charge of an electron is determined to be -1.60×10-19coulombs coulombs representing charge.

OK, so just realize that when it came to the Milliken oil drop experiment, it helped to further the experiment of Thompson. It helped us to figure out the amount of negative charge on any given electron, yeah.

Millikan Oil Drop Experiment Example 1

We're told that the fundamental charge of an electron is -1.60×10-19 Coulombs. If a scientist determines the charge to mass ratio of an electron is -1.76×108 Coulombs/gram, what will be the total mass of an electron?

All right, so for a question like this, they want us to determine the total Max. So that is what our end amount needs to be. So end amount here will be the grams of our electrons and our given amount. Remember our given amount is when we have a value that has only one unit connected to it and here that one unit by itself would be this charge of an electron. So that's our given amount 1.60×10-19 coulombs. Remember, don't forget the negative sign.

Now to go from the given amount to the end amount, we have to utilize conversion factors. Remember, conversion factor is when you have two units tied together. Our conversion factor here would be -1.76×108 coulombs/gram. Coulombs and grams are two different units that are being tied together. We need to cancel out Coulombs. So we put the -1.76×108 Coulombs on the bottom and that's for everyone Gram. So this would represent our conversion factor, and we'd see here that Coulombs would cancel out and have as my units at the end grams, which is what I'm looking for.

So all we have to say here is this question requires only one conversion factor. So then it's just going to be this value here divided by this value here and that'll give us our grams. Remember, when you have a number written in scientific notation, you need to put it in parentheses, otherwise you may get the incorrect answer. If you do this correctly, you'll get approximately 9.10×10-28 g as the total mass of your electron. So based on that answer, option B would be the correct choice.

Here’s what students ask on this topic:

What was the oil drop experiment?

The oil drop experiment, conducted by Robert A. Millikan and Harvey Fletcher in 1909, was a pivotal experiment designed to measure the electric charge of a single electron. The setup involved spraying tiny oil droplets into a chamber and allowing them to pass through a hole into an electrically charged area between two metal plates. By adjusting the voltage across the plates, Millikan and Fletcher were able to balance the gravitational force on an oil droplet with the electric force, causing the droplet to suspend in mid-air.

By carefully observing the behavior of the oil droplets and knowing the density of the oil, they could calculate the mass of a droplet. Combining this with the electric force allowed them to determine the charge on the droplet. Through repeated experiments with different droplets, they noticed that the charges were always multiples of a certain smallest value, which they determined to be the charge of a single electron. This experiment provided the first accurate value of the electron's charge, which is a fundamental constant in physics.

What scientist proposed the oil drop experiment?

The oil drop experiment was proposed and conducted by American physicist Robert A. Millikan, with the help of his graduate student Harvey Fletcher. This groundbreaking experiment took place in 1909 at the University of Chicago. Millikan's objective was to measure the electric charge of a single electron, which he achieved by carefully observing the behavior of tiny oil droplets suspended between two electrically charged plates. By adjusting the voltage across the plates and analyzing the rate of the droplets' rise or fall, Millikan was able to determine the charge on the droplets, which in turn led to the calculation of the fundamental charge of the electron. This experiment played a crucial role in the development of atomic physics by providing the first accurate value of the electron's charge, a fundamental constant in physics.

What did Robert Millikan's oil drop experiment prove?

Robert Millikan's oil drop experiment, conducted in 1909, was pivotal in proving the existence of electrically charged particles, which we now know as electrons. The experiment allowed Millikan to calculate the charge of a single electron with high precision. By carefully observing the behavior of tiny oil droplets between two electrically charged plates, Millikan was able to determine how the droplets were suspended in the electric field. By adjusting the strength of the electric field, he could measure the amount of charge needed to counteract the gravitational force on the droplets. This groundbreaking work provided the first accurate value of the electron's charge, which is approximately:

$-1.602\times {10}^{-19}\text{coulombs}$

Millikan's findings supported and quantified the atomic theory of matter, confirming that electric charge is quantized, meaning it exists in discrete packets rather than being continuous. This experiment was a significant step forward in the field of atomic physics.