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Millikan oil-drop experiment

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• PhysicsLAB - Millikan's Oil Drop Experiment

Millikan oil-drop experiment , first direct and compelling measurement of the electric charge of a single electron . It was performed originally in 1909 by the American physicist Robert A. Millikan , who devised a straightforward method of measuring the minute electric charge that is present on many of the droplets in an oil mist. The force on any electric charge in an electric field is equal to the product of the charge and the electric field. Millikan was able to measure both the amount of electric force and magnitude of electric field on the tiny charge of an isolated oil droplet and from the data determine the magnitude of the charge itself.

Millikan’s original experiment or any modified version, such as the following, is called the oil-drop experiment. A closed chamber with transparent sides is fitted with two parallel metal plates, which acquire a positive or negative charge when an electric current is applied. At the start of the experiment, an atomizer sprays a fine mist of oil droplets into the upper portion of the chamber. Under the influence of gravity and air resistance, some of the oil droplets fall through a small hole cut in the top metal plate. When the space between the metal plates is ionized by radiation (e.g., X-rays ), electrons from the air attach themselves to the falling oil droplets, causing them to acquire a negative charge. A light source, set at right angles to a viewing microscope , illuminates the oil droplets and makes them appear as bright stars while they fall. The mass of a single charged droplet can be calculated by observing how fast it falls. By adjusting the potential difference, or voltage, between the metal plates, the speed of the droplet’s motion can be increased or decreased; when the amount of upward electric force equals the known downward gravitational force, the charged droplet remains stationary. The amount of voltage needed to suspend a droplet is used along with its mass to determine the overall electric charge on the droplet. Through repeated application of this method, the values of the electric charge on individual oil drops are always whole-number multiples of a lowest value—that value being the elementary electric charge itself (about 1.602 × 10 −19 coulomb). From the time of Millikan’s original experiment, this method offered convincing proof that electric charge exists in basic natural units. All subsequent distinct methods of measuring the basic unit of electric charge point to its having the same fundamental value.

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Milliken's Oil Drop Experiment

The Millikens Oil Drop Experiment was an experiment performed by Robert A. Millikan and Harvey Fletcher  in 1909 to measure the charge of an electron. This experiment proved to be very crucial in the physics community.

Millikens Oil Drop Experiment Definition

In the experiment, Milliken allowed charged tiny oil droplets to pass through a hole into an electric field. By varying the strength of the electric field the charge over an oil droplet was calculated, which always came as an integral value of ‘e.’

Apparatus of the Milliken’s Oil Drop Experiment

The apparatus for the experiment was constructed by Milliken and Fletcher. It incorporated two metal plates held at a distance by an insulated rod. There were four holes in the plate, out of which three were there to allow light to pass through them and one was there to allow viewing through the microscope.

Ordinary oil wasn’t used for the experiment as it would evaporate by the heat of the light and so could cause an error in the Millikens Oil Drop Experiment. So, the oil that is generally used in a vacuum apparatus which is of low vapour pressure was used.

Milliken’s Oil Drop Experiment Procedure

• Oil is passed through the atomizer from where it came in the form of tiny droplets. They pass the droplets through the holes present in the upper plate of the apparatus.
• The downward motions of droplets are observed through a microscope and the mass of oil droplets, then measure their terminal velocity.
• The air inside the chamber is ionized by passing a beam of X-rays through it. The electrical charge on these oil droplets is acquired by collisions with gaseous ions produced by ionization of air.
• The electric field is set up between the two plates and so the motion of charged oil droplets can be affected by the electric field.
• Gravity attracts the oil in a downward direction and the electric field pushes the charge upward. The strength of the electric field is regulated so that the oil droplet reaches an equilibrium position with gravity.
• The charge over the droplet is calculated at equilibrium, which is dependent on the strength of the electric field and mass of droplet.

Milliken’s Oil Drop Experiment Calculation

F up = F down

F up = Q . E

F down = m.g

Q  is  an  electron’s  charge,  E  is  the  electric  field,  m  is  the  droplet’s  mass,  and  g  is  gravity.

One can see how an electron charge is measured by Millikan. Millikan found that all drops had charges that were 1.6x 10 -19 C multiples.

Milliken’s Oil Drop Experiment Conclusion

The charge over any oil droplet is always an integral value of e (1.6 x 10 -19 ). Hence, the conclusion of  Millikens Oil Drop Experiment is that the charge is said to be quantized, i.e. the charge on any particle will always be an integral multiple of e.

Frequently Asked Questions – FAQs

What did millikan’s oil drop experiment measure.

Millikan oil-drop test, the first simple and persuasive electrical charge calculation of a single electron. It was first conducted by the American physicist Robert A. in 1909. He discovered that all the drops had charges that were simple multiples of a single integer, the electron’s fundamental charge.

What is the importance of Millikan’s oil drop experiment?

The experiment with Millikan is important since it defined the charge on an electron. Millikan used a very basic, very simple system in which the behaviour of gravitational, electrical, and (air) drag forces were controlled.

What did Millikan conclude after performing his oil drop experiment?

An integral multiple of the charge on an electron is the charge on every oil decrease. About an electric force. In a relatively small amount, the charge and mass of the atom must be condensed.

Why charges are quantized?

Charges are quantized since every object’s charge (ion, atom, etc.) Charge quantization, therefore, implies that no random values can be taken from the charge, but only values that are integral multiples of the fundamental charge (proton / electron charge).

Can charge be created or destroyed?

The Charge Conservation Law does not suggest that it is difficult to generate or remove electrical charges. It also means that any time a negative electrical charge is produced, it is important to produce an equal amount of positive electrical charge at the same time so that a system’s overall charge does not shift.

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August, 1913: Robert Millikan Reports His Oil Drop Results

Robert Millikan’s famous oil drop experiment , reported in August 1913, elegantly measured the fundamental unit of electric charge. The experiment, a great improvement over previous attempts to measure the charge of an electron, has been called one of the most beautiful in physics history, but is also the source of allegations of scientific misconduct on Millikan’s part.

Robert Millikan was born in 1868 and grew up in rural Iowa, the second son of a minister. Millikan attended Oberlin College, earned his PhD from Columbia University, and then spent a year in Germany before taking a position at the University of Chicago.

By about 1906, Millikan had become a successful educator and textbook writer, but he knew that he hadn’t done any research of real scientific significance, and was eager to make his mark as a researcher.

J.J. Thomson had discovered the electron in 1897 and had measured its charge-to-mass ratio. The next step was to determine the electron’s charge separately. Thomson and others tried to measure the fundamental electric charge using clouds of charged water droplets by observing how fast they fell under the influence of gravity and an electric field. The method did give a crude estimate of the electron’s charge.

Millikan saw this opportunity to make a significant contribution by improving upon these measurements. He realized that trying to determine the charge on individual droplets might work better than measuring charge on whole clouds of water. In 1909 he began the experiments, but soon found that droplets of water evaporated too quickly for accurate measurement. He asked his graduate student, Harvey Fletcher, to figure out how to do the experiment using some substance that evaporated more slowly.

Fletcher quickly found that he could use droplets of oil, produced with a simple perfume atomizer. The oil droplets are injected into an air-filled chamber and pick up charge from the ionized air. The drops then fall or rise under the combined influence of gravity, viscosity of the air, and an electric field, which the experimenter can adjust. The experimenter could watch the drops through a specially designed telescope, and time how fast a drop falls or rises. After repeatedly timing the rise and fall of a drop, Millikan could calculate the charge on the drop.

In 1910 Millikan published the first results from these experiments, which clearly showed that charges on the drops were all integer multiples of a fundamental unit of charge. But after the publication of those results, Viennese physicist Felix Ehrenhaft claimed to have conducted a similar experiment, measuring a much smaller value for the elementary charge. Ehrenhaft claimed this supported the idea of the existence of “subelectrons.”

Ehrenhaft’s challenge prompted Millikan to improve on his experiment and collect more data to prove he was right. He published the new, more accurate results in August 1913 in the Physical Review . He stated that the new results had only a 0.2% uncertainty, a great improvement of over his previous results. Millikan’s reported value for the elementary charge, 1.592 x 10 -19 coulombs, is slightly lower than the currently accepted value of 1.602 x 10 -19 C, probably because Millikan used an incorrect value for the viscosity of air.

It appeared that it was a beautiful experiment that had determined quite precisely the fundamental unit of electric charge, and clearly and convincingly established that “subelectrons” did not exist. Millikan won the 1923 Nobel Prize for the work, as well as for his determination of the value of Plank’s constant in 1916.

But later inspection of Millikan’s lab notebooks by historians and scientists has revealed that between February and April 1912, he took data on many more oil drops than he reported in the paper. This is troubling, since the August 1913 paper explicitly states at one point, “It is to be remarked, too, that this is not a selected group of drops, but represents all the drops experimented upon during 60 consecutive days.” However, at another point in the paper he writes that the 58 drops reported are those “upon which a complete series of observations were made.” Furthermore, the margins of his notebook contain notes such as, “beauty publish” or “something wrong.”

Did Millikan deliberately disregard data that didn’t fit the results he wanted? Perhaps because he was under pressure from a rival and eager to make his mark as a scientist, Millikan misrepresented his data. Some have called this a clear case of scientific fraud. However, other scientists and historians have looked closely at his notebooks, and concluded that Millikan was striving for accuracy by reporting only his most reliable data, not trying to deliberately mislead others. For instance, he rejected drops that were too big, and thus fell too quickly to be measured accurately with his equipment, or too small, which meant they would have been overly influenced by Brownian motion. Some drops don’t have complete data sets, indicating they were aborted during the run.

It’s difficult to know today whether Millikan intended to misrepresent his results, though some scientists have examined Millikan’s data and calculated that even if he had included all the drops in his analysis, his measurement for the elementary charge would not have changed much at all.

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Who Did the Oil Drop Experiment?

The Oil Drop Experiment was performed by the American physicist Robert A Millikan in 1909 to measure the electric charge carried by an electron . Their original experiment, or any modifications thereof to reach the same goal, are termed as oil drop experiments, in general.

What is the Oil Drop Experiment?

In the original version, Millikan and one of his graduate students, Harvey Fletcher, took a pair of parallel horizontal metallic plates. A uniform electric field was created in the intermediate space by applying a potential difference between them. The plates were held apart by a ring of insulating material. The ring had four holes, three for allowing light to illuminate the setup, and the fourth one enabled a microscope for viewing. A closed chamber with transparent walls was fitted above the plates.

At the beginning of the experiment, a fine mist of oil droplets was sprayed into the chamber. In modern setups, an atomizer replaces the oil droplets. The oil was so chosen such that it had a low vapor pressure and capable of charging. Some of the oil drops became electrically charged by friction as they forced their way out of the nozzle. Alternatively, charging could also be induced by incorporating a source of ionizing radiation , such as an X-Ray tube, in the apparatus. The droplets entered the space between the plates and raised or fell, according to the requirement, by varying plate voltage.

In terms of the present-day arrangement, when the electric field is turned off, the oil drops fall between the plates under the action of gravity only. The friction with the oil molecules in the chamber makes them reach their terminal velocity fast. The terminal velocity is the constant speed that a freely falling object eventually reaches when the resistance of the medium through which it is falling prevents further acceleration . Once the field is turned on, the charged drops start to rise. This motion happens since the electric force directed upwards is stronger than the gravitational force acting downwards. One charged drop is selected and kept at the center of the field of view of the microscope after allowing all other drops to fall by alternately switching off the voltage source. The experiment is conducted with this drop.

Theory and Calculations

First, the oil drop is allowed to fall in the absence of an electric field, and its terminal velocity, say v 1 , is found out. Using Stokes’ law, the drag force acting on the drop is calculated using the following formula.

Here r is the radius of the drop and ɳ, the viscosity of air.

The weight of the drop, w’, which is the product of its mass and acceleration due to gravity g, is given by the equation,

where ρ is the density of the oil.

However, what we need here is the apparent weight w of the drop in the air given by the difference of the actual weight and the upthrust of the air. We can express w  by the following formula.

Here ρ air denotes the density of air.

When the drop attains terminal velocity, then it has no acceleration. Hence, the total force acting on it must be zero. That means,

The above equation can be used to find out the value of r. Once r is calculated, the value of w can easily be found out from equation (i) marked above.

Now after turning on the electric field between the plates, the electric force F E acting on the drop is,

Where E is the electric field and q the charge on the oil drop. For parallel plates, the formula for E is,

Here V is the potential difference and d the distance between the plates. That implies,

Now if we adjust V to make the oil drop remain steady at a point, then

Thus, the value of q can be calculated.  By repeatedly applying this method to multiple oil droplets, the electric charge values on individual drops were always found to be integer multiples of the smallest value. This lowest charge could be nothing but the charge on the elementary particle, electron. By this method, the electronic charge was calculated to be approximate, 1.5924×10 −19  C, making an error of 1% of the currently accepted value, 1.602176487×10 −19 C. All subsequent research pointed to the same value of charge on the fundamental particle.

Millikan was able to measure both the amount of electric force and magnitude of electric field on the tiny charge of an isolated oil droplet and from the data determine the magnitude of the charge itself. Millikan’s oil drop experiment proved that the electric charge is quantized in nature. The electric charge appears in quanta of magnitude 1.6 X 10 -19 C in oil droplets.

Robert Millikan’s Oil Drop Experiment Animation

Millikan’s oil drop experiment and the atomic theory.

Until the time of the Oil Drop Experiment, the world had little or no knowledge of what is present inside an atom . Earlier experiments by the English Physicist J.J. Thomson had shown that atoms contain some negatively charged particles of masses significantly smaller than that of the hydrogen atom. Nevertheless, the exact value of the charge carried by these subatomic particles remained in the dark. The very existence of these particles was not accepted by many due to a lack of concrete evidence. Thus, the atomic model was shrouded in mystery. In this scenario, with Millikan’s groundbreaking effort to quantify the charge on an electron, the atomic theory came of age in the early years of the twentieth century.

Controversy about the Oil Drop Experiment and Discovery

Robert Millikan was the sole recipient of the Nobel Prize in Physics in 1923 for both his work in this classic experiment and his research in the photoelectric effect . Fletcher’s work on the oil drop project, however, was not recognized. Many years later, the writings of Fletcher revealed that Millikan wished to take the sole credit for the discovery in exchange for granting him a Ph.D. and helping him secure a job after his graduation.

The beauty of the oil drop experiment lies in its simple and elegant demonstration of the quantization of charge along with measuring the elementary charge on an electron that finds widespread applications to this day. With the progress of time, considerable modifications have been made to the original setup resulting in obvious perfection in the results. Still, no substantial deviation from the results of the classical experiment could yet be found.

• Robert Millikan and Harvey Fletcher conducted the oil drop experiment to determine the charge of an electron. The experiment was the first direct and riveting measurement of the electric charge of a single electron.
• They suspended tiny charged droplets of oil between two metal electrodes by balancing downward gravitational force with upward drag and electric forces.
• They later used their findings to determine the mass of the electron.
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Article was last reviewed on Thursday, February 2, 2023

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The Millikan Oil Drop Experiment

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Robert Millikan's oil drop experiment measured the charge of the electron . The experiment was performed by spraying a mist of oil droplets into a chamber above the metal plates. The choice of oil was important because most oils would evaporate under the heat of the light source, causing the drop to change mass throughout the experiment. Oil for vacuum applications was a good choice because it had a very low vapor pressure. Oil droplets could become electrically charged through friction as they were sprayed through the nozzle or they could be charged by exposing them to ionizing radiation . Charged droplets would enter the space between the parallel plates. Controlling the electric potential across the plates would cause the droplets to rise or fall.

Calculations for the Experiment

F d = 6πrηv 1

where r is the drop radius, η is the viscosity of air and v 1 is the terminal velocity of the drop.

The weight W of the oil drop is the volume V multiplied by the density ρ and the acceleration due to gravity g.

The apparent weight of the drop in air is the true weight minus the upthrust (equal to the weight of air displaced by the oil drop). If the drop is assumed to be perfectly spherical then the apparent weight can be calculated:

W = 4/3 πr 3 g (ρ - ρ air )

The drop is not accelerating at terminal velocity so the total force acting on it must be zero such that F = W. Under this condition:

r 2 = 9ηv 1 / 2g(ρ - ρ air )

r is calculated so W can be solved. When the voltage is turned on the electric force on the drop is:

F E = qE

where q is the charge on the oil drop and E is the electric potential across the plates. For parallel plates:

E = V/d

where V is the voltage and d is the distance between the plates.

The charge on the drop is determined by increasing the voltage slightly so that the oil drop rises with velocity v 2 :

qE - W = 6πrηv 2

qE - W = Wv 2 /v 1

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The Millikan Oil Drop Experiment

Introduction To The Millikan Oil Drop Experiment

In this article, you will learn all you need to know (and more) about the Millikan Oil Drop Experiment. If you like this article, check out our other articles!

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Who was Robert A. Millikan?

Robert A. Millikan was born on the 22nd of March, 1868 in Illinois, (U.S.A.). Growing up, Millikan spent most of his childhood living in a rural town called Morrison. Then, in 1875, his family relocated to Maquoketa, Iowa where Millikan started attending Maquoketa high school. Millikan excelled in his learning and decided to further his studies by attending Oberlin College in Ohio. During this time, Millikan started teaching a physics class and decided to pursue the subject as a career. He later obtained his Ph.D. in physics from Columbia University.

After graduating from Columbia, Millikan traveled to the universities of Berlin and Göttingen. There, he furthered his knowledge within his field before returning to the United States to be an assistant at Chicago University’s Ryerson Laboratory. During his time there, Millikan authored (and co-authored) several physics textbooks. Eventually, in 1907, a research project of Millikan’s led to the development of the Oil Drop Experiment .

The Experiment

Devised by Robert A. Millikan and Harvey Fletcher, the Millikan Oil Drop Experiment is conducted in a chamber and is a method of measuring the electric charge of a single electron .

To elaborate, this chamber contains an atomizer, a microscope, a light source, and two parallel metal plates. These metal plates obtain a negative and a positive charge when an electric current would pass through them.

The Procedure

First, the atomizer was to release a fine mist of oil that would drift within the chamber. While drifting, the droplets of oil would make their way into the bottom half of the chamber (between the metal plates) due to a gravitational pull. Here, the oil droplets would be ionized into being negatively charged. Thereafter, while these negatively charged droplets are being pulled down by gravity, the external power-dial would be used to add a charge to the two metal plates (above and below the droplets). Specifically speaking, the  top  plate would cultivate a  positive  charge, and a  negative  charge would be cultivated on the  bottom  plate.

This creates a situation in which the oppositely charged (positive) metal plate is pulling the negatively charged droplet upwards , while gravity is pulling the droplet downwards . Or in other words, the electrostatic and gravitational forces are now controlling the direction in which the droplet is flowing. Now, if the electrostatic force is greater, then the droplet would rise towards the positively charged plate. Likewise, if the gravitational force is greater than the electrostatic force, then the droplet would be pulled down.

Observations and Conclusion

The purpose of this experiment was to balance these two electrostatic and gravitational forces – which would cause the droplets to halt midair. By doing this, the droplet’s mass, gravitational force, and electrostatic force could be measured, revealing the charge of the electron. Furthermore, by doing these final calculations, Millikan was able to reveal that the charge of an electron would be multiples of  1.602×10−19 Coulombs .

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Key Questions

Millikan suspended oil droplets between two electric plates and determined their charges.

He used an apparatus like that below:

Oil droplets from a fine mist fell through a hole in the upper floor. From their terminal velocity, he could calculate the mass of each drop.

Millikan then used x-rays to ionize the air in the chamber. Electrons attached themselves to the oil drops.

He adjusted the voltage between two plates above and below the chamber, so that the drop would hang suspended in mid-air.

Millikan calculated the mass and the force of gravity on one drop and calculated the charge on a drop. The charge was always a multiple of -1.6 x 10⁻¹⁹ C. He proposed that this was the charge on an electron.

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Landmarks —Millikan Measures the Electron’s Charge

Landmarks articles feature important papers from the archives of the Physical Review journals.

Researchers now routinely isolate single electrons in quantum dots, but a century ago the state-of-the-art charge-trapping device was a droplet of clock oil. Robert Millikan’s oil drop experiment provided the first clear measurement of the fundamental electric charge and thus helped cement the notion that nature is “grainy” at the smallest level. The first results came out in 1910, but the seminal work was a 1913 paper in the Physical Review . Millikan reported a value for the fundamental electric charge that was within half a percent of today’s accepted value. The experiment helped earn Millikan a Nobel prize in 1923 but has been a source of some controversy over the years.

J. J. Thomson discovered the electron in 1897 when he measured the charge-to-mass ratio for electrons in a beam. But the value of the charge and whether it was fundamental remained open questions. Thomson and others tried to measure an irreducible electric charge by looking at clouds of water droplets. Using various techniques, they estimated the smallest charge that a droplet could hold, but the results were not entirely convincing because they relied on averages over many particles of various sizes. “The evidence for a unitary charge was at the time very ambiguous,” says science historian Gerald Holton of Harvard University.

At the University of Chicago in the 1900s, Millikan and his graduate students realized that ramping up the electric field would disperse a water cloud, so that only a few droplets remained. He decided to try isolating single droplets, but it soon became clear that single water droplets evaporated too quickly to make reliable measurements. One of his students, Harvey Fletcher, found that long-lasting droplets could be made with a light oil that was used for lubricating clocks.

The oil drop experiment that Millikan and Fletcher designed had two chambers. In the upper chamber, an atomizer (like that used in perfume bottles) dispersed a fine mist of micron-sized oil droplets. Individual droplets would fall through a pinhole into the lower chamber, which consisted of two horizontal plates, with one held 16 millimeters above the other. The air in this chamber was ionized with x rays , so that ions or free electrons could be captured on the falling droplets. A small window on the side allowed the scientists to observe the droplets through a telescope. The droplets fell slowly enough—due to atmospheric drag—that the researchers could measure their downward speed by eye, using horizontal lines in the telescope. From this speed, they could estimate the size and mass of each droplet.

They then applied a high voltage across the plates and measured the upward speed of the droplet, to determine the electric force and ultimately the charge. Multiple measurements on a single droplet could be performed by repeatedly turning the electric field on and off. The droplets had various amounts of charge on them (and they would often gain or lose charge during an observation), but the data showed that the charge was indeed quantized into integer multiples of a unit charge.

In 1910 Millikan published the first results of these experiments [1] (Fletcher was not included as an author, based on a deal the two struck [2] ). Millikan then made several improvements, including an empirical estimate of the drag forces. The culmination of this effort, reported in 1913, was a value of the fundamental charge with an error bar of just 0.2 percent. The precision acquired was so great that “other experiments did not improve on his result until a decade later,” Holton says.

But Felix Ehrenhaft of the University of Vienna repeatedly challenged Millikan’s results, based on his own measurements of “sub-electron” charges on small metal particles. The dispute lasted for many years—known as the “Battle over the Electron”—but eventually most physicists sided with Millikan.

In more recent years, historians who have examined Millikan’s lab notes have said that he discarded some of the measurements to boost the evidence of a fundamental charge. But David Goodstein of the California Institute of Technology in Pasadena believes these accusations of fraud are unwarranted. He has analyzed the notes and says that Millikan excluded droplets because their observations were incomplete, not because their implied charge didn’t match his expectations [3] . “Millikan’s oil drop experiment is a classic example of outstanding physics done by one of the giants of his era,” Goodstein says.

–Michael Schirber

Michael Schirber is a Corresponding Editor for  Physics Magazine based in Lyon, France.

• R. A. Millikan, “The Isolation of an Ion, a Precision Measurement of its Charge, and the Correction of Stokes’s Law,” Science 32 , 436 (1910) ; first reported at the American Physical Society meeting, 23 April 1910, Phys. Rev. (Series I) 30 , 656 (1910)
• H. Fletcher, “My work with Millikan on the oil‐drop experiment,” Phys. Today 35 , 43 (1982)
• D. Goodstein, “In Defense of Robert Andrews Millikan,” Am. Sci. 89 , 54 (2001)

More Information

Focus story on Millikan’s measurement of Planck’s constant

article by Gerald Holton on the Millikan-Ehrenhaft Dispute

article about the ethics of Millikan’s handling of data

Millikan Nobel Prize: Nobel lecture, biography, and other information

On the Elementary Electrical Charge and the Avogadro Constant

R. A. Millikan.

Phys. Rev. 2 , 109 (1913)

Published August 1, 1913

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Today in Science History – December 19 – Robert Millikan and Oil Drops

December 19 marks the passing of Robert Millikan. Millikan was an American physicist best known for his famous oil drop experiment.

The purpose of this experiment was to measure the charge of an electron . Millikan and Harvey Fletcher sprayed charged drops of oil between two horizontal charged plates. Gravity pulls the oil drops down while electrostatic forces between the drops and the charged plate pull the drops upwards. As the drops were suspended, they could measure their diameters and calculate their volume. They then used the density of the oil to determine the mass of each drop.

To account for air resistance as the drops fell, they applied Stokes Law to calculate the drag the drop encounters as it falls. This force changes the apparent weight of the drop as it falls through the air. Both forces could be balanced by applying a voltage to the parallel plates. The electrostatic force applied to balance these forces is directly proportional to the charge of the oil drop.

When this experiment is run against multiple oil drops the resulting charges all have a common factor of one unit of electrical charge or the charge of a single electron. Millikan and Fletcher’s value for the charge of an electron was 1.5924(17)×10 −19 Coulombs. Today, the accepted value for the charge of an electron is 1.602176487(40)×10 −19 Coulombs. The measurement of this fundamental constant earned Millikan the 1923 Nobel Prize in Physics and Harvey Fletcher his doctorate degree.

Notable Science History Events for December 19

2013 – esa launches gaia telescope..

The European Space Agency launched their Gaia spacecraft. Gaia was designed to create a 3D map of nearly one billion stellar objects. The equipment on board would take 70 different observations of each object to determine it’s position, velocity, and parallax over the course of its five-year run. The spacecraft’s instruments have managed to maintain their integrity better than hoped and plans are in place to increase the mission.

2004 – Herbert Charles Brown died.

Brown was an Anglo-American chemist who was awarded half the 1979 Nobel Prize in Chemistry for his development of organoborane chemistry. Organoboranes are organic compounds which have boron and hydrogen together and are used in many transformation reactions.

1961 – Eric Allin Cornell was born.

Cornell is an American physicist who shares the 2001 Nobel Prize in Physics with Carl Wieman and Wolfgang Ketterie for synthesizing the first Bose-Einstein condensate (BEC). A Bose-Einstein condensate is a state of matter where a dilute gas near absolute zero where all particles occupy the lowest quantum state and the quantum effects appear on a macroscopic level. This achievement verified the existence of BEC predicted by Satyendra Bose and Albert Einstein in 1924.

1953 – Robert Andrews Millikan died.

1936 – juan de la cierva died..

Cierva was a Spanish civil engineer who invented the autogyro. An autogyro is an aircraft that uses a rotary wing system to provide lift. The autogyro uses a conventional propeller to pull the aircraft forward which starts the gyro rotating and the aircraft begins to fly. This invention led directly to the invention of the helicopter.

1903 – George Davis Snell was born.

Snell was an American geneticist who discovered the genetic factors involved to determine whether or not a transplant of tissue from one organism to another is possible. This would earn him one-third of the 1980 Nobel Prize in Medicine.

1852 – Albert Abraham Michelson was born.

Michelson was an American physicist best known for his quest to accurately measure the speed of light. He was also the Michelson from the Michelson/Morley experiment to disprove the existence of the aether, the medium of space. He developed many new precision optical devices to refine his measurement of the speed of light and was awarded the 1909 Nobel Prize in Physics for his efforts.

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Dalton's Model of the Atom / J.J. Thomson / Millikan's Oil Drop Experiment / Rutherford / Niels Bohr / DeBroglie / Heisenberg / Planck / Schrödinger / Chadwick from- http://en.wikipedia.org/wiki/Oil_drop_experiment With this data and J.J. Thompsons charge to mass  ratio the mass of the electron could be calculated. 1.5924×10  C  x = 9.04 x 10 g or 9.04 x 10 kg  the accepted value is 9.109 x 10 kg   1.76 x 10 C Chemical Demonstration Videos Want to create or adapt books like this? Learn more about how Pressbooks supports open publishing practices. Chapter 2 Electric Charge and Electric Field 2.2 Discovery of the Parts of the Atom: Electrons and Nuclei – Millikan Oil Drop Experiment and Rutherford Scattering Describe how electrons were discovered. Explain the Millikan oil drop experiment. Describe Rutherford’s gold foil experiment. Describe Rutherford’s planetary model of the atom. Just as atoms are a substructure of matter, electrons and nuclei are substructures of the atom. The experiments that were used to discover electrons and nuclei reveal some of the basic properties of atoms and can be readily understood using ideas such as electrostatic and magnetic force, already covered in previous chapters. Charges and Electromagnetic Forces In previous discussions, we have noted that positive charge is associated with nuclei and negative charge with electrons. We have also covered many aspects of the electric and magnetic forces that affect charges. We will now explore the discovery of the electron and nucleus as substructures of the atom and examine their contributions to the properties of atoms. The Electron Gas discharge tubes, such as that shown in Figure 1 , consist of an evacuated glass tube containing two metal electrodes and a rarefied gas. When a high voltage is applied to the electrodes, the gas glows. These tubes were the precursors to today’s neon lights. They were first studied seriously by Heinrich Geissler, a German inventor and glassblower, starting in the 1860s. The English scientist William Crookes, among others, continued to study what for some time were called Crookes tubes, wherein electrons are freed from atoms and molecules in the rarefied gas inside the tube and are accelerated from the cathode (negative) to the anode (positive) by the high potential. These “ cathode rays ” collide with the gas atoms and molecules and excite them, resulting in the emission of electromagnetic (EM) radiation that makes the electrons’ path visible as a ray that spreads and fades as it moves away from the cathode. Gas discharge tubes today are most commonly called cathode-ray tubes , because the rays originate at the cathode. Crookes showed that the electrons carry momentum (they can make a small paddle wheel rotate). He also found that their normally straight path is bent by a magnet in the direction expected for a negative charge moving away from the cathode. These were the first direct indications of electrons and their charge. But the vertical deflection is also related to the electron’s mass, since the electron’s acceleration is The value of  the force F   is not known, since q e   was not yet known. Substituting the expression for electric force into the expression for acceleration yields Gathering terms, we have This is a huge number, as Thomson realized, and it implies that the electron has a very small mass. It was known from electroplating that about 10 8 C/kg  is needed to plate a material, a factor of about 1000 less than the charge per kilogram of electrons. Thomson went on to do the same experiment for positively charged hydrogen ions (now known to be bare protons) and found a charge per kilogram about 1000 times smaller than that for the electron, implying that the proton is about 1000 times more massive than the electron. Today, we know more precisely that Thomson performed a variety of experiments using differing gases in discharge tubes and employing other methods, such as the photoelectric effect, for freeing electrons from atoms. He always found the same properties for the electron, proving it to be an independent particle. For his work, the important pieces of which he began to publish in 1897, Thomson was awarded the 1906 Nobel Prize in Physics. In retrospect, it is difficult to appreciate how astonishing it was to find that the atom has a substructure. Thomson himself said, “It was only when I was convinced that the experiment left no escape from it that I published my belief in the existence of bodies smaller than atoms.” Thomson attempted to measure the charge of individual electrons, but his method could determine its charge only to the order of magnitude expected. In the Millikan oil drop experiment, fine drops of oil are sprayed from an atomizer. Some of these are charged by the process and can then be suspended between metal plates by a voltage between the plates. In this situation, the weight of the drop is balanced by the electric force: The electric field is produced by the applied voltage, hence,  E =V/d , and  V is adjusted to just balance the drop’s weight. The drops can be seen as points of reflected light using a microscope, but they are too small to directly measure their size and mass. The mass of the drop is determined by observing how fast it falls when the voltage is turned off. Since air resistance is very significant for these submicroscopic drops, the more massive drops fall faster than the less massive, and sophisticated sedimentation calculations can reveal their mass. Oil is used rather than water, because it does not readily evaporate, and so mass is nearly constant. Once the mass of the drop is known, the charge of the electron is given by rearranging the previous equation: where d is the separation of the plates and V  is the voltage that holds the drop motionless. (The same drop can be observed for several hours to see that it really is motionless.) By 1913 Millikan had measured the charge of the electron q e  to an accuracy of 1%, and he improved this by a factor of 10 within a few years to a value of  -1.60 x  10 -19 C . He also observed that all charges were multiples of the basic electron charge and that sudden changes could occur in which electrons were added or removed from the drops. For this very fundamental direct measurement of q e   and for his studies of the photoelectric effect, Millikan was awarded the 1923 Nobel Prize in Physics. https://www.nobelprize.org/prizes/physics/1923/summary/ With the charge of the electron known and the charge-to-mass ratio known, the electron’s mass can be calculated. It is Substituting known values yields or                                                               m e = 9.11 x 10 – 31   kg where the round-off errors have been corrected. The mass of the electron has been verified in many subsequent experiments and is now known to an accuracy of better than one part in one million. It is an incredibly small mass and remains the smallest known mass of any particle that has mass. (Some particles, such as photons, are massless and cannot be brought to rest, but travel at the speed of light.) A similar calculation gives the masses of other particles, including the proton. To three digits, the mass of the proton is now known to be Another important characteristic of quantum mechanics was also beginning to emerge. All electrons are identical to one another. The charge and mass of electrons are not average values; rather, they are unique values that all electrons have. This is true of other fundamental entities at the submicroscopic level. All protons are identical to one another, and so on. The Nucleus Here, we examine the first direct evidence of the size and mass of the nucleus. In later chapters, we will examine many other aspects of nuclear physics, but the basic information on nuclear size and mass is so important to understanding the atom that we consider it here. Nuclear radioactivity was discovered in 1896, and it was soon the subject of intense study by a number of the best scientists in the world. Among them was New Zealander Lord Ernest Rutherford, who made numerous fundamental discoveries and earned the title of “father of nuclear physics.” Born in Nelson, Rutherford did his postgraduate studies at the Cavendish Laboratories in England before taking up a position at McGill University in Canada where he did the work that earned him a Nobel Prize in Chemistry in 1908. In the area of atomic and nuclear physics, there is much overlap between chemistry and physics, with physics providing the fundamental enabling theories. He returned to England in later years and had six future Nobel Prize winners as students. Rutherford used nuclear radiation to directly examine the size and mass of the atomic nucleus. The experiment he devised is shown in Figure 7 . A radioactive source that emits alpha radiation was placed in a lead container with a hole in one side to produce a beam of alpha particles, which are a type of ionizing radiation ejected by the nuclei of a radioactive source. A thin gold foil was placed in the beam, and the scattering of the alpha particles was observed by the glow they caused when they struck a phosphor screen. PhET simulation.  Direct link:   https://phet.colorado.edu/sims/html/rutherford-scattering/latest/rutherford-scattering_en.html  Alpha particles were known to be the doubly charged positive nuclei of helium atoms that had kinetic energies on the order of  5 MeV   when emitted in nuclear decay, which is the disintegration of the nucleus of an unstable nuclide by the spontaneous emission of charged particles. These particles interact with matter mostly via the Coulomb force, and the manner in which they scatter from nuclei can reveal nuclear size and mass. This is analogous to observing how a bowling ball is scattered by an object you cannot see directly. Because the alpha particle’s energy is so large compared with the typical energies associated with atoms  MeV  versus eV (in other words 1 million times greater) , you would expect the alpha particles to simply crash through a thin foil much like a supersonic bowling ball would crash through a few dozen rows of bowling pins. Thomson had envisioned the atom to be a small sphere in which equal amounts of positive and negative charge were distributed evenly. The incident massive alpha particles would suffer only small deflections in such a model. Instead, Rutherford and his collaborators found that alpha particles occasionally were scattered to large angles, some even back in the direction from which they came! Detailed analysis using conservation of momentum and energy—particularly of the small number that came straight back—implied that gold nuclei are very small compared with the size of a gold atom, contain almost all of the atom’s mass, and are tightly bound. Since the gold nucleus is several times more massive than the alpha particle, a head-on collision would scatter the alpha particle straight back toward the source. In addition, the smaller the nucleus, the fewer alpha particles that would hit one head on. Although the results of the experiment were published by his colleagues in 1909, it took Rutherford two years to convince himself of their meaning. Like Thomson before him, Rutherford was reluctant to accept such radical results. Nature on a small scale is so unlike our classical world that even those at the forefront of discovery are sometimes surprised. Rutherford later wrote: “It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you. On consideration, I realized that this scattering backwards … [meant] … the greatest part of the mass of the atom was concentrated in a tiny nucleus.” In 1911, Rutherford published his analysis together with a proposed model of the atom. The size of the nucleus was determined to be about  10 -15 m , or 100,000 times smaller than the atom. This implies a huge density, on the order of  10 -15   g / cm 3    , vastly unlike any macroscopic matter. Also implied is the existence of previously unknown nuclear forces to counteract the huge repulsive Coulomb forces among the positive charges in the nucleus. Huge forces would also be consistent with the large energies emitted in nuclear radiation. The small size of the nucleus also implies that the atom is mostly empty inside. In fact, in Rutherford’s experiment, most alphas went straight through the gold foil with very little scattering, since electrons have such small masses and since the atom was mostly empty with nothing for the alpha to hit. There were already hints of this at the time Rutherford performed his experiments, since energetic electrons had been observed to penetrate thin foils more easily than expected. Figure 8 shows a schematic of the atoms in a thin foil with circles representing the size of the atoms (about  10 -10 m  and dots representing the nuclei. (The dots are not to scale—if they were, you would need a microscope to see them.) Most alpha particles miss the small nuclei and are only slightly scattered by electrons. Occasionally, (about once in 8000 times in Rutherford’s experiment), an alpha hits a nucleus head-on and is scattered straight backward. Based on the size and mass of the nucleus revealed by his experiment, as well as the mass of electrons, Rutherford proposed the planetary model of the atom . The planetary model of the atom pictures low-mass electrons orbiting a large-mass nucleus. The sizes of the electron orbits are large compared with the size of the nucleus, with mostly vacuum inside the atom. This picture is analogous to how low-mass planets in our solar system orbit the large-mass Sun at distances large compared with the size of the sun. In the atom, the attractive Coulomb force is analogous to gravitation in the planetary system. (See Figure 9 .) Note that a model or mental picture is needed to explain experimental results, since the atom is too small to be directly observed with visible light. Rutherford’s planetary model of the atom was crucial to understanding the characteristics of atoms, and their interactions and energies, as we shall see in the next few sections. Also, it was an indication of how different nature is from the familiar classical world on the small, quantum mechanical scale. The discovery of a substructure to all matter in the form of atoms and molecules was now being taken a step further to reveal a substructure of atoms that was simpler than the 92 elements then known. We have continued to search for deeper substructures, such as those inside the nucleus, with some success. In later chapters, we will follow this quest in the discussion of quarks and other elementary particles, and we will look at the direction the search seems now to be heading. PhET Explorations: Rutherford Scattering How did Rutherford figure out the structure of the atom without being able to see it? Simulate the famous experiment in which he disproved the Plum Pudding model of the atom by observing alpha particles bouncing off atoms and determining that they must have a small core. Section Summary Atoms are composed of negatively charged electrons, first proved to exist in cathode-ray-tube experiments, and a positively charged nucleus. All electrons are identical and have a charge-to-mass ratio of q e  / m e   = 1.76 x 10 11    C/kg The positive charge in the nuclei is carried by particles called protons, which have a charge-to-mass ratio of                            q p  / m p   = 9.57 x 10 7    C/kg Mass of electron, m e = 9.11  x 10 -31 kg Mass of proton, m p  = 1.67  x 10 -27 kg The planetary model of the atom pictures electrons orbiting the nucleus in the same way that planets orbit the sun. Conceptual Questions 1: What two pieces of evidence allowed the first calculation of m e , the mass of the electron? (a) The ratios q e / m e and q p /m p (b) The values  q e   and  E/B (c) The ratio  q e / m e and  q e   Justify your response. 2: How do the allowed orbits for electrons in atoms differ from the allowed orbits for planets around the sun? Explain how the correspondence principle applies here. Problem Exercises 1: Rutherford found the size of the gold nucleus to be about  10 -15 m.  This implied a huge density. What would this density be for gold? 2:  In Millikan’s oil-drop experiment, one looks at a small oil drop held motionless between two plates. Take the voltage between the plates to be 2033 V, and the plate separation to be 2.00 cm. The oil drop of density 810 kg / m 3   has a diameter 4.0  x 10 -6 m . Find the charge on the drop, a) in coulombs and then b) in terms of electron units. 3: (a) An aspiring physicist wants to build a scale model of a hydrogen atom for her science fair project. If the atom is 1.00 m in diameter, how big should she try to make the nucleus?   Assume the diameter of the hydrogen nucleus is 1 x 10 -15 m while that of the atom is 1 angstrom or 1 x 10 -10 m. (b) How easy will this be to do? 1:   6  x  10 20 {kg/m}^3 2: In Millikan’s oil-drop experiment, one looks at a small oil drop held motionless between two plates. Take the voltage between the plates to be 2033 V, and the plate separation to be 2.00 cm. The oil drop of density 810 kg / m 3   has a diameter 4.0 x 10 -6 m . Find the charge on the drop, in terms of electron units. 2:  Worked out answer:   density = mass / volume so  mass = (density) ( volume ) = (density) ( 4 / 3  π  r 3 ) mass =  2.17 x 10 -14  kg net force = 0 N as it is suspended   gravity force = electric force     m g = q E  = q (Voltage/gap width) q = m g d / Voltage  = 2.09 x 10 – 17 C a) 2.09 x 10 -18 C  b) 13 electrons 3: (a) 1 x 10 -5 m = 10 x 10 -6 m = 10 microns = 10 μm (b) It isn’t hard to make one of approximately this size. It would be harder to make it exactly 10 μm. Douglas College Physics 1207 Copyright © August 22, 2016 by OpenStax is licensed under a Creative Commons Attribution 4.0 International License , except where otherwise noted. Stack Exchange Network Stack Exchange network consists of 183 Q&A communities including Stack Overflow , the largest, most trusted online community for developers to learn, share their knowledge, and build their careers. Q&A for work Connect and share knowledge within a single location that is structured and easy to search. How did Millikan measure the mass of these oil droplets? I was reading the R.A. Millikan's oil drop experiment and the following part confused me: By measuring the rate of fall, Millikan was able to measure the fall of the oil droplets (which were dropped through a tiny hole in the upper electrical condenser). In Newtonian physics, the rate of fall (or velocity) of a freely falling body does not depend on the mass of the object. So, how did Millikan measure the mass of these oil droplets? Does anyone know the equations he used? history-of-chemistry 5 $\begingroup$ Have you checked Wikipedia? en.wikipedia.org/wiki/Oil_drop_experiment $\endgroup$ –  user9974 Commented May 5, 2015 at 5:10 $\begingroup$ You can find out here: youtube.com/watch?v=ijHKu6iXiRk $\endgroup$ –  LDC3 Commented May 5, 2015 at 5:59 $\begingroup$ Have a look at aip.org/history/gap/PDF/millikan.pdf $\endgroup$ –  Klaus-Dieter Warzecha Commented May 5, 2015 at 6:01 By measuring the rate of fall, Millikan was able to measure the fall of the oil droplets (which were dropped through a tiny hole in the upper electrical condenser) The rate of fall here means terminal velocity of oil, $v_\mathrm{t}.$ Oil was made to drop at constant rate so no acceleration. Drag force on oil drop is: $$F_\mathrm{d} = 6\pi r\eta v_\mathrm{t},\tag{1}$$ where $r$ is the radius of oil drop and $\eta$ is the viscosity of air. Assume oil droplet is spherical. Apparent weight of oil droplet in air is the true weight minus the upthrust (which equals the weight of air displaced by the oil drop). So, it can be written as: $$w = \frac{4\pi r^3(\rho - \rho_\mathrm{air})g}{3}.\tag{2}$$ No acceleration is taking place so the total force acting on it must be zero and thus the two forces must cancel each other (i.e $F_\mathrm{d} = w).$ Solving for $r$ gives $$r = \sqrt{\frac{9\eta v_\mathrm{t}}{2g(\rho - \rho_\mathrm{air})}}.\tag{3}$$ The density of oil is known so by known so by putting $r,$ you can calculate the mass of oil droplet as $$m = \rho V = \rho\frac{4\pi r^3}{3}.\tag{4}$$ Your Answer Reminder: Answers generated by artificial intelligence tools are not allowed on Chemistry Stack Exchange. Learn more Sign up or log in Post as a guest. Required, but never shown By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy . Not the answer you're looking for? 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Examples of distribution for which first-order condition is not enough for MLE What is the translation of misgendering in French? 249 IMAGES Millikan oil-drop experiment PPT Millikens Oil Drop Experiment Millikan Oil Drop Experiment Animation 11C02 Millikens Oil Drop Experiment VIDEO Oil drop experiment ( class -11) Lec Millikan's Oil Drop Experiment || part 03 ||determined charge an electron class 11 Atomic structure In an oil drop experiment, the following charges (in arbitrary unit OIL DROP EXPERIMENT QUESTIONS. PAPER 1 PHYSICS THE OIL DROP EXPERIMENT QUESTIONS COMMENTS Millikan oil-drop experiment Millikan's original experiment or any modified version, such as the following, is called the oil-drop experiment. A closed chamber with transparent sides is fitted with two parallel metal plates, which acquire a positive or negative charge when an electric current is applied. At the start of the experiment, an atomizer sprays a fine mist of oil droplets into the upper portion of the chamber. Oil drop experiment The oil drop experiment was performed by Robert A. Millikan and Harvey Fletcher in 1909 to measure the elementary electric charge (the charge of the electron ). [1] [2] The experiment took place in the Ryerson Physical Laboratory at the University of Chicago. [3] [4] [5] Millikan received the Nobel Prize in Physics in 1923. Millikens Oil Drop Experiment Milliken's Oil Drop Experiment Calculation. F up = F down. F up = Q . F down = m.g. Q is an electron's charge, E is the electric field, m is the droplet's mass, and g is gravity. One can see how an electron charge is measured by Millikan. Millikan found that all drops had charges that were 1.6x 10 -19 C multiples. 4.12: Oil Drop Experiment The oil drops picked up static charge and were suspended between two charged plates. Millikan was able to observe the motion of the oil drops with a microscope and found that the drops lined up in a specific way between the plates, based on the number of electric charges they had acquired. Figure 4.12.2 4.12. 2: Oil Drop experiment. August, 1913: Robert Millikan Reports His Oil Drop Results Robert Millikan. Robert Millikan's famous oil drop experiment, reported in August 1913, elegantly measured the fundamental unit of electric charge. The experiment, a great improvement over previous attempts to measure the charge of an electron, has been called one of the most beautiful in physics history, but is also the source of allegations ... Millikan's Oil Drop Experiment: How to Determine the Charge of an Millikan's experiment is based on observing charged oil droplets in free fall and the presence of an electric field. A fine mist of oil is sprayed across the top of a perspex cylinder with a small 'chimney' that leads down to the cell (if the cell valve is open). The act of spraying will charge some of the released oil droplets through friction ... Millikan's Oil Drop Experiment The experiment is conducted with this drop. Theory and Calculations. First, the oil drop is allowed to fall in the absence of an electric field, and its terminal velocity, say v 1, is found out. Using Stokes' law, the drag force acting on the drop is calculated using the following formula. The Millikan Oil Drop Chemistry Experiment The Millikan Oil Drop Experiment. Robert Millikan's oil drop experiment measured the charge of the electron. The experiment was performed by spraying a mist of oil droplets into a chamber above the metal plates. The choice of oil was important because most oils would evaporate under the heat of the light source, causing the drop to change mass ... The Millikan Oil Drop Experiment The Experiment. Devised by Robert A. Millikan and Harvey Fletcher, the Millikan Oil Drop Experiment is conducted in a chamber and is a method of measuring the electric charge of a single electron. To elaborate, this chamber contains an atomizer, a microscope, a light source, and two parallel metal plates. These metal plates obtain a negative ... Millikan's Oil Drop Experiment Millikan suspended oil droplets between two electric plates and determined their charges. Oil droplets from a fine mist fell through a hole in the upper floor. From their terminal velocity, he could calculate the mass of each drop. Millikan then used x-rays to ionize the air in the chamber. Electrons attached themselves to the oil drops. Physics The oil drop experiment that Millikan and Fletcher designed had two chambers. In the upper chamber, an atomizer (like that used in perfume bottles) dispersed a fine mist of micron-sized oil droplets. Individual droplets would fall through a pinhole into the lower chamber, which consisted of two horizontal plates, with one held 16 millimeters ... Millikan's Oil Drop Experiment Millikan's experiment was meant to have the drops fall at a constant rate. At this constant rate, the force of gravity on the drop and the force of the electric field on the drop are equal: F up = F down. Q is the charge of an electron, E is the electric field, m is mass of the droplet, and g is gravity. December 19 December 19 marks the passing of Robert Millikan. Millikan was an American physicist best known for his famous oil drop experiment. The purpose of this experiment was to measure the charge of an electron. Millikan and Harvey Fletcher sprayed charged drops of oil between two horizontal charged plates. Gravity pulls the oil drops down while ... Oil Drop Experiment The oil drop experiment is an experiment that allows a precise meaurement of the elementary charge e e. The experiment was developed and performed in 1910 by the american physicist Robert Andrews Millikan. He measured the following value for the elementary charge: e =1.592 ⋅10−19C e = 1.592 ⋅ 10 − 19 C. Nowadays there are more precise ... Charge of an Electron: Millikan's Oil Drop Experiment To see all my Chemistry videos, check outhttp://socratic.org/chemistryHow did scientists discover how much negative charge an electron had? Robert Millikan a... Millikan's Oil Drop Experiment The oil drop experiment was an experiment performed by Robert Millikan and Harvey Fletcher in 1909 to measure the elementary electric charge (the charge of the electron).. The experiment entailed balancing the downward gravitational force with the upward buoyant and electric forces on tiny charged droplets of oil suspended between two metal electrodes. Oil-drop experiment The purpose of Robert Millikan and Harvey Fletcher's oil-drop experiment (1909) was to measure the electric charge of the electron.They did this by carefully balancing the gravitational and electric forces on tiny charged droplets of oil suspended between two metal electrodes.Knowing the electric field, the charge on the oil droplet could be determined. PDF Millikan Oil Drop Experiment Summary as of January 2007 •Total mass throughput for all experiments: 351.4 milligrams of fluid •Total drops measured in all experiments: 105.6 million •No evidence for fractionally charged particleswas found. Measuring the Electron Charge. Physics 401 31. •1909: Oil drop experiment, Robert A. Millikan. 2.2 Discovery of the Parts of the Atom: Electrons and Nuclei 2: In Millikan's oil-drop experiment, one looks at a small oil drop held motionless between two plates. Take the voltage between the plates to be 2033 V, and the plate separation to be 2.00 cm. The oil drop of density 810 kg / m 3 has a diameter 4.0 x 10-6 m . Find the charge on the drop, a) in coulombs and then b) in terms of electron units. The Millikan oil drop experiment The Millikan oil drop experiment is a landmark of modern physics, since it allowed it to be proved for the first time that electric charge is discrete, and to measure the elementary unit of charge. In this chapter, after a brief historical introduction, we describe this experiment in detail, with a careful treatment of the physics involved. Millikan Oil Drop Experiment: Definition, Apparatus, Procedures The famous Millikan's oil drop experiment was designed with the same aim and also was a first step towards the target. The experiment took place in the Ryerson Physical Laboratory (RPL) at the University of Chicago. By measuring the deflection produced in the charged oil droplets, Millikan was able to prove the existence of electrons. He was ... The Oil Drop Experiment What Millikan did was to put a charge on a tiny drop of oil, and measure how strong an applied electric field had to be in order to stop the oil drop from falling. Since he was able to work out the mass of the oil drop, and he could calculate the force of gravity on one drop, he could then determine the electric charge that the drop must have ... How did Millikan measure the mass of these oil droplets? By measuring the rate of fall, Millikan was able to measure the fall of the oil droplets (which were dropped through a tiny hole in the upper electrical condenser). In Newtonian physics, the rate of fall (or velocity) of a freely falling body does not depend on the mass of the object. essay homework paper phd project resume review speech thesis