NTNUJAVA Virtual Physics Laboratory
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Easy Java Simulations (2001- ) => modern physics => Topic started by: ahmedelshfie on July 21, 2010, 06:05:09 pm

Title: Millikan oil drop experiment
Post by: ahmedelshfie on July 21, 2010, 06:05:09 pm
This following applet is Millikan oil drop experiment
Created by prof Hwang Modified by Ahmed
Original project Millikan oil drop experiment (http://www.phy.ntnu.edu.tw/ntnujava/index.php?topic=357.0)

Oil-drop experiment was the 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. Using a perfume atomizer, he sprayed tiny drops of oil into a transparent chamber. At the top and bottom were metal plates hooked to a battery, making one positive (red in animation) and the other negative (blue in animation). Since each droplet picked up a slight charge of static electricity as it traveled through the air, the speed of its motion could be controlled by altering the voltage on the plates. When the space between the metal plates is ionized by radiation (e.g., X rays), electrons from the air attach themselves to oil droplets, causing them to acquire a negative charge. Millikan observed one drop after another, varying the voltage and noting the effect. After many repetitions he concluded that charge could only assume certain fixed values. The smallest of these portions was none other than the charge of a single electron.

Turn voltage on/off when you hear warning sound (if you did not turn on "auto" mode)

The oil will drop down due to gravity and reach terminal velocity (v1).
Please turn on voltage when oil almost reach the bottom of the plate (click the "Voltage on/off"  checkbox at the lower left corner of the applet)
The oil drop will move up and reach another terminal velocity (v2).
From v1,v2 and voltage you can calculate the charge on the oil drop (may be 1-5 electron --assigned randomly)

You can change the voltage between parallel plate, and you will get different terminal velocity v2, and voltage U. But the calculated value for the charge will be the same).
Click "change Q" will change the number of electron on the oil drop.
Click "new drop" will create another oil drop (different size and different charge).
If you click auto, the simulation will turn on/off voltage automatically.

Title: Re: Millikan oil drop experiment
Post by: ahmedelshfie on July 23, 2010, 05:20:40 pm
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. Since the density of the oil was known, the droplets' masses, and therefore their gravitational and buoyant forces, could be determined from their observed radii. Using a known electric field, Millikan and Fletcher could determine the charge on oil droplets in mechanical equilibrium. By repeating the experiment for many droplets, they confirmed that the charges were all multiples of some fundamental value, and calculated it to be 1.5924(17)×10−19 C, within one percent of the currently accepted value of 1.602176487(40)×10−19 C. They proposed that this was the charge of a single electron.

Starting in 1900, while a professor  at the University of Chicago, Millikan, with the significant input of Fletcher[1], and after improving his setup, published his seminal study in 1913.[2]

His experiment measured the force on tiny charged droplets of oil suspended against gravity between two metal electrodes. Knowing the electric field, the charge on the droplet was determined. Repeating the experiment for many droplets, Millikan showed that the results could be explained as integer multiples of a common value (1.592×10−19 C), the charge on a single electron.

At the time of Millikan and Fletcher's oil drop experiments, the existence of subatomic particles was not universally accepted. Experimenting with cathode rays in 1897, J. J. Thomson had discovered negatively charged "corpuscles", as he called them, with a mass about 1000 times smaller than that of a hydrogen atom. Similar results had been found by George FitzGerald and Walter Kaufmann. Most of what was then known about electricity and magnetism, however, could be explained on the basis that charge is a continuous variable; in much the same way that many of the properties of light can be explained by treating it as a continuous wave rather than as a stream of photons.

The so-called elementary charge e is one of the fundamental physical constants and its accurate value is of great importance. In 1923, Millikan won the Nobel Prize in physics in part because of this experiment.

Aside from the measurement, the beauty of the oil drop experiment is that it is a simple, elegant hands-on demonstration that charge is actually quantized. Thomas Edison, who had previously thought of charge as a continuous variable, became convinced after working with Millikan and Fletcher's apparatus. This experiment has since been repeated by generations of physics students, although it is rather expensive and difficult to do properly.
Data and images from  http://en.wikipedia.org/wiki/Oil_drop_experiment

Title: Re: Millikan oil drop experiment
Post by: ahmedelshfie on August 02, 2010, 05:40:13 pm
Here is a youtube video explain about Millikan oil drop experiment.