results of millikan's oil drop experiment

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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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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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Millikan’s Oil Drop Experiment ( AQA A Level Physics )

Revision note.

Millikan's Oil Drop Experiment

• This experiment was conducted by Millikan and Fletcher in 1909
• It determined the value of fundamental or e = 1.60 × 10 -19 C An electron has a charge - e and a proton has a charge + e " data-title="Elementary Charge (e)" data-toggle="popover">elementary charge

Method for Millikan's Oil Drop Experiment

• Oil is used instead of water because it does not evaporate quickly
• This means the mass of the drops will remain constant
• This consequently changes their charge from neutral
• They will become positively charged if they lose electrons 
• They will become negatively charged if they gain electrons
• The drops pass into a region between two metal plates and are viewed using a microscope

Equipment Set Up for Millikan's Oil Drop Experiment

In Millikan's Oil Drop Experiment oil is sprayed into a chamber before passing between metal plates where the electric and gravitational forces are compared

Condition for Stationary Oil Drops

• Negative oil drops with magnitude of charge Q  experience an upward force from the uniform electric field 
• The magnitude of this force F  is:
• For this to occur, the force  F  has to be equal to the weight of the oil drop, mg , so there is no resultant vertical force on each drop
• Therefore, the condition under which oil drops are held stationary is:
• For that, Milikan needed to determine the mass of each oil drop, so he used Stokes' Law

Worked example

One particular oil drop had a mass of 5.1 × 10 -15 kg. It is held stationary between two charged plates. These are separated by 12 mm and there is a potential difference of 1250 V across them.

Calculate the charge of the oil drop.

Step 1: List the known quantities:

• Mass,  m = 5.1 × 10 -15 kg
• Separation of plates,  d = 12 mm
• Potential difference,  V = 1250 V
• Acceleration due to gravity,  g = 9.81 m s -2

Step 2: Recall the condition for a stationary oil drop:

• The condition for the oil drop not to fall or rise:

Step 3: Rearrange this equation to calculate charge:

• Make charge the subject:

The condition for a stationary oil droplet is given in the equation sheet. Focus your revision on using  it and understanding where it comes from, as opposed to memorising the equation.

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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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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.
• Kentchemistry.com
• Physics.utah.edu
• Nobelprize.org
• Ffden-2.phys.uaf.edu
• Chem.libretexts.org

Article was last reviewed on Thursday, February 2, 2023

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Introduction to Chemistry

Millikan's oil drop experiment, learning objective.

• Describe the major findings of Millikan's oil drop experiment
• Millikan's oil drop experiment measured the charge of an electron. Before this experiment, existence of subatomic particles was not universally accepted.
• Millikan's apparatus contained an electric field created between a parallel pair of metal plates, which were held apart by insulating material. Electrically charged oil droplets entered the electric field and were balanced between two plates by altering the field.
• When the charged drops fell at a constant rate, the gravitational and electric forces on it were equal. Therefore, the charge on the oil drop was calculated using formula Q = m ⋅ g E \frac {m\cdot g}{E} E m ⋅ g ​ Millikan found that the charge of a single electron was 1.6 x 10 -19 C.
• oil drop experimentExperiment performed by Robert Millikan and Harvey Fletcher in 1909 to measure the charge of the electron.
• electronThe subatomic particle having a negative charge and orbiting the nucleus; the flow of electrons in a conductor constitutes electricity.

The Oil Drop Experiment

How did the process work.

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