what charge must plate Y have in order to cause a negatively charged droplet to move upward
Learning Objective
- Describe the major findings of Millikan'due south oil drib experiment
Key Points
- Millikan'due south oil drib experiment measured the charge of an electron. Before this experiment, existence of subatomic particles was not universally accepted.
- Millikan'south apparatus independent an electric field created between a parallel pair of metal plates, which were held apart by insulating material. Electrically charged oil aerosol entered the electric field and were balanced betwixt two plates by altering the field.
- When the charged drops barbarous 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 = [latex]\frac {m\cdot g}{E}[/latex] Millikan found that the charge of a single electron was ane.6 x 10-xix C.
Terms
- oil drop experimentExperiment performed past 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 Driblet Experiment
In 1909, Robert Millikan and Harvey Fletcher conducted the oil drop experiment to determine the charge of an electron. They suspended tiny charged droplets of oil between 2 metal electrodes by balancing downward gravitational force with upwardly elevate and electrical forces. The density of the oil was known, so Millikan and Fletcher could make up one's mind the droplets' masses from their observed radii (since from the radii they could calculate the volume and thus, the mass). Using the known electric field and the values of gravity and mass, Millikan and Fletcher determined the charge on oil droplets in mechanical equilibrium. By repeating the experiment, they confirmed that the charges were all multiples of some fundamental value. They calculated this value to be 1.5924 × 10−19Coulombs (C), which is within 1% of the currently accepted value of 1.602176487 × 10−xix C. They proposed that this was the charge of a single electron.
How did the process work?
The figure below shows a simplified scheme of Millikan's oil driblet experiment. The apparatus incorporated a pair of metallic plates and a specific type of oil. Millikan and Fletcher discovered it was best to use an oil with an extremely low vapor pressure, such equally one designed for utilise in a vacuum appliance. Ordinary oil would evaporate under the heat of the light source, causing the mass of the oil drib to alter over the course of the experiment.
Past applying a potential departure across a parallel pair of horizontal metal plates, a compatible electric field was created in the space between them. A ring of insulating material was used to concur the plates apart. Four holes were cut into the ring—3 for illumination past a bright light and another to allow viewing through a microscope. A fine mist of oil aerosol was sprayed into a sleeping accommodation above the plates. The oil drops became electrically charged through friction with the nozzle every bit they were sprayed. Alternatively, charge could be induced by including an ionizing radiations source (such as an X-ray tube).
The aerosol entered the space betwixt the plates and, because they were charged, they could be controlled past changing the voltage beyond the plates. Initially, the oil drops were immune to fall between the plates with the electric field turned off. They apace reached terminal velocity due to friction with the air in the bedchamber. The field was turned on and, if information technology was large enough, some of the drops (the charged ones) would start to ascent. This is because the upwardly electrical force, FE , is greater for them than the downwards gravitational strength, g. (A charged rubber rod can selection up $.25 of paper in the same fashion.) A likely looking drib was selected and kept in the middle of the field of view by alternately switching off the voltage until all the other drops fell. The experiment was continued with this single drib.
Millikan's experiment was meant to have the drops fall at a constant rate. At this constant rate, the strength of gravity on the drop and the strength of the electric field on the drop are equal:
Fup = Fdownwards
[latex]\cdot[/latex]Fup = Q[latex]\cdot[/latex]E Fdown = thou[latex]\cdot[/latex]
Q is the accuse of an electron, Due east is the electric field, m is mass of the droplet, and thousand is gravity.
Q[latex]\cdot[/latex]E = grand[latex]\cdot[/latex]g
Q = [latex]\frac{yard\cdot g}{E}[/latex]
I can see how Millikan calculated the charge of an electron. Millikan constitute that all drops had charges which were multiples of one.vi x x-nineteen C.
At the time of Millikan and Fletcher's oil drib experiments, the existence of subatomic particles was not universally accepted. Experimenting with cathode rays in 1897, J. J. Thomson discovered negatively charged "corpuscles" with a mass about 1,840 times smaller than that of a hydrogen cantlet. George FitzGerald and Walter Kaufmann found like results. In 1923, Millikan won the Nobel Prize in physics in function because of this experiment.
Aside from discerning an electron'due south charge, the dazzler of the oil drib experiment lies in its simple and elegant sit-in that accuse is really quantized. The experiment has since been repeated by generations of physics students—although it is rather expensive and difficult to do properly.
Source: https://courses.lumenlearning.com/introchem/chapter/millikans-oil-drop-experiment/
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