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An American physicist, Robert Millikan (1868–1953) (see [link] ), decided to improve upon Thomson’s experiment for measuring q e size 12{q rSub { size 8{e} } } {} and was eventually forced to try another approach, which is now a classic experiment performed by students. The Millikan oil drop experiment is shown in [link] .

Black and white image of physicist Robert Millikan wearing a jacket and a bow tie.
Robert Millikan (credit: Unknown Author, via Wikimedia Commons)
Image of the apparatus used in the Millikan oil drop experiment, consisting of a parallel pair of horizontal metal plates with a pin hole opening in the top plate. The top plate has positive charge and the bottom plate has negative charge. Picture of a flashlight as a bright source of light and a beam of light passing in between the plates from left is shown. A telescope is shown at the front and an oil atomizer above the positive plate is also depicted. A zoomed image of metal plates describing the force acting on the oil droplet is also shown. Arrows pointing upwards are forces of electric field while arrows pointing downwards depict the force of gravity.
The Millikan oil drop experiment produced the first accurate direct measurement of the charge on electrons, one of the most fundamental constants in nature. Fine drops of oil become charged when sprayed. Their movement is observed between metal plates with a potential applied to oppose the gravitational force. The balance of gravitational and electric forces allows the calculation of the charge on a drop. The charge is found to be quantized in units of −1.6 × 10 −19 C , thus determining directly the charge of the excess and missing electrons on the oil drops.

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:

m drop g = q e E size 12{m rSub { size 8{"drop"} } g=q rSub { size 8{e} } E} {}

The electric field is produced by the applied voltage, hence, E = V / d size 12{E=V/d} {} , and V size 12{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:

q = m drop g E = m drop gd V , size 12{q= { {m rSub { size 8{"drop"} } g} over {E} } = { {m rSub { size 8{"drop"} } ital "gd"} over {V} } ,} {}

where d size 12{d} {} is the separation of the plates and V size 12{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 size 12{q rSub { size 8{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 × 10 19 C size 12{ - 1 "." "60" times "10" rSup { size 8{ - "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 size 12{q rSub { size 8{e} } } {} and for his studies of the photoelectric effect, Millikan was awarded the 1923 Nobel Prize in Physics.

With the charge of the electron known and the charge-to-mass ratio known, the electron’s mass can be calculated. It is

m = q e q e m e . size 12{m= { {q rSub { size 8{e} } } over { left ( { {q rSub { size 8{e} } } over {m rSub { size 8{e} } } } right )} } "." } {}

Substituting known values yields

m e = 1.60 × 10 19 C 1 . 76 × 10 11 C/kg size 12{m rSub { size 8{e} } = { { - 1 "." "60" times "10" rSup { size 8{ - "19"} } " C"} over { - 1 "." "76" times "10" rSup { size 8{"11"} } {C} slash {"kg"} } } } {}

or

m e = 9 . 11 × 10 31 kg (electron’s mass), size 12{m rSub { size 8{e} } =9 "." "11" times "10" rSup { size 8{ - "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

Questions & Answers

Application of nanotechnology in medicine
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scanning tunneling microscope
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if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
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analytical skills graphene is prepared to kill any type viruses .
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what is Nano technology ?
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write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
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what king of growth are you checking .?
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What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
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why we need to study biomolecules, molecular biology in nanotechnology?
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Introduction about quantum dots in nanotechnology
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nano basically means 10^(-9). nanometer is a unit to measure length.
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Source:  OpenStax, College physics -- hlca 1104. OpenStax CNX. May 18, 2013 Download for free at http://legacy.cnx.org/content/col11525/1.1
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