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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.
- Structure of Atom
- Oil Drop Experiment
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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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 .
Further Reading
School Chemistry Projects (on ScienceBuddies)
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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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.
Chemical Demonstration VideosDescription This simulation is a simplified version of an experiment done by Robert Milliken in the early 1900s. Hoping to learn more about charge, Milliken sprayed slightly ionized oil droplets into an electric field and made observations of the droplets. When the voltage is zero and the run button is pressed, the drop will fall due to the force of gravity. It will reach a terminal velocity (v t ) as it falls. Pause the simulation while you record the terminal velocity. This terminal velocity can be used to determine the mass of the drop. Use the equation: mass = kv t 2 to determine the mass of the particle. The value of k in this simulation is 4.086 x 10 -17 kg s 2 /m 2 . Once the terminal velocity is recorded and the mass calculated, with the simulation still paused increase the voltage between the plates until the two force vectors are approximately equal length. This will produce an upward field and an upward force on the positive droplets. If the upward force of the electric field is equal to the downward force of gravity, and the drag force is zero, the particle will not accelerate. To be sure that the lack of acceleration is not related to drag forces, the velocity must also be zero as well as the acceleration in order to be sure that the two forces are balanced. Increase and decrease the voltage (use the left/right arrow keys) until both the acceleration and velocity are at zero. The velocity may not stay at exactly zero, but find the voltage that has the velocity changing most slowly as it passes v = 0. Use the methods discussed above to ultimately determine the charge on ten (or more) different oil-drops. Use V = Ed to calculate the field strength (d = 5 cm = 0.05 m). Use Eq = mg when the velocity is zero to determine the charge q on the droplet. Record all your data in a table or spreadsheet. After you get each q, create a new particle and start again. When you have the table filled in, look at the various values for q. Is there any pattern to them, or are they seemingly random? Can you draw any conclusions from the Q measurements?  |
COMMENTS
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 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. [ 6]
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.
A description of the historic oil drop experiment that was performed by Robert Millikan to determine the electrical charge of the electron. Included is a diagram of the apparatus used and a discussion of the forces acting on the oil droplets.
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 ...
This experiment first described in 1913, is based on the fact that diferent forces act on an electrically charged oil drop moving in the homogeneous electric field of a plate capacitor (Figure 1). Going through the capillary of the atomizer, the oil droplets acquire electric charge due to friction. The efect is known as triboelectric charging.
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. ⋅ \cdot ⋅. F up = Q. ⋅ \cdot ⋅. E F down = m. ⋅ \cdot ⋅. Q is the charge of an electron, E is the electric field, m is mass of ...
This experiment first described in 1913, is based on the fact that different forces act on an electrically charged oil drop moving in the homogeneous electric field of a plate capacitor (Fig.1). Going through the capillary of the atomizer, the oil droplets acquire electric charge due to friction. The effect is known as triboelectri c charging.
Balance of Forces: Newton's Law a : radius of drop ρ: density ρ= ρ oil -ρ air v: velocity of oil drop Q: charge of oil drop E: electric field E=V/d V : Voltage across plates η: viscosity of air g : gravitational const. Ö ()) 6 1) dr g dr a ag E g E Fa gz FQ dv F v t E d SK Ö zg 6SK vrag QEE Forces on the oil drop:
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 ...
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 ...
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. [Figure1] This is the original equipment used by Robert Millikan and Harvey Fletcher in 1909 at the Univeristy of Chicago to measure the electric charge on a single electron. With incredible perserverence, they were able to determine the charge to within 1% of the currently accepted value.
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.
In 1909, Robert Millikan and Harvey Fletcher developed an experiment to determine the fundamental charge of the electron. This was achieved by measuring the charge of oil drops in a known electric field. If all electrons have the same charge, then the measured charge on the oil drops must be multiples of the same fundamental constant.
Description. This simulation is a simplified version of an experiment done by Robert Milliken in the early 1900s. Hoping to learn more about charge, Milliken sprayed slightly ionized oil droplets into an electric field and made observations of the droplets. When the voltage is zero and the run button is pressed, the drop will fall due to the ...
In this experiment you will experimentally determine the quantum nature of charge. Robert Millikan was awarded the Nobel Prize in physics in 1923 for this brilliant experiment. A simplistic schematic of his apparatus is shown below. A spherical drop of oil, falling through a viscous medium like air, will quickly reach a constant velocity.
Oil drop experiment. V +-V g d 500V telescope atomizer Oil drops ∅~1m 𝝆𝒂 𝒓 Forces on the oil drop: 1) Gravity + buoyant force (air displaced by oil drop) 2) Drag force of the oil drop in the air 3) Electric force on oil drops which carry charge Q 9/22/2014 8
Experimental. The charges of the oil drop for the 37 measurements in Table I of Millikan's work (1) are shown in the second col-umn of Table 1. The charges are sorted into descending or-der in column 3. Column 4 shows the differences between adjacent rows and represents the charge difference between two experiments.
Millikan's original experiment is very tedious and time consuming. This applet includes a number of simplifications: • only one drop is observed rather than many drops; • each drop has a random charge assuming some charging method; Millikan used friction of drops from an atomizer spray and ionizing X-rays to charge the drops; • drops ...
Millikan Oil Drop Lab. In this lab you will be looking for oil drops that can caught in the electric field between two capacitor plates. Some drops will fall out of your field of view as the gravitational force on them is larger than the electric force. Other drops will rise out of your field of view as the gravitational force is too small for ...
1. An oil drop of 12 excess electrons is held stationary under a constant electric field of 2.55 x 104V/m in Millikan’s oil drop experiment. The density of the oil drop is 1.26 cgs units. Estimate the radius of the oil drop. 2. Use the simulation and find out the charge on any five drops.