ROBERT ANDREWS MILLIKAN By: Tritany, Rhi and Amayia

SCIENTIST’S BACKGROUND  Born March 22, 1868; Died on December 19, 1953  Lived in Morrison, Illinois; San Marino, California  Parents: Rev. Silas Franklin Millikan and Mary Jane Andrews  Brothers: Allan Fairchild Millikan, Max Franklin Millikan  Sisters: Marjorie Avis Millikan Johnson, Mary Grace Millikan Behr, Mabel Aurelia Millikan Brown  Wife: Greta Ervin Blanchard  Children: Clark Blanchard Millikan, Glenn Allen Millikan, Max Franklin Millikan  He attended Maquoketa Community High School located in Iowa, then went to Oberlin College located in Ohio in 1886

CONTINUED BACKGROUND INFO.  For two years he taught elementary Physics; In 1893 he was appointed Fellow in Physics at Columbia University after obtaining his Masters in Physics  “He afterwards received his Ph.D. in 1895 for research on the polarization of light emitted by incandescent surfaces-using for this purpose molten gold and silver at the US Mint.” (Robert A. Millikan – Biographical)  “As a scientist, Millikan made numerous momentous discoveries, chiefly in the fields of electricity, optics, and molecular physics. His earliest major success was the accurate determination of the charge carried by an electron, using the elegant “falling-drop method”: he also proved that this quantity was a constant for all electrons(1910), thus demonstrating the atomic structure of electricity.” (Robert A. Millikan – Biographical)

DATES OF IMPORTANCE RELATED TO THE ATOMIC THEORY  he received his Ph.D. for research on the polarization of light emitted by incandescent surfaces  conducted the oil drop experiments  he proved that this quantity (coulomb) was a constant for all electrons  he made the first direct photoelectric determination of Planck's constant “H”  he occupied himself with work concerning the hot spark spectroscopy of the elements (explored the region of the spectrum b/t the ultraviolet and x- radiation)  he won the Nobel Prize for Physics

OIL DROP EXPERIMENT

DESCRIPTION OF EXPERIMENTAL DESIGN  Atomizer  Battery  2 charged plates  Microscope  Oil droplets  Coulomb- (C); it is a unit of electric charge and a dimensionless quantity. 1C is equal to approximately 6.24 X 10^18 ; it is equivalent to one ampere second based on SI units.

PROCEDURES INVOLVED IN THE EXPERIMENT 1. The atomizer sprays a mist of oil droplets in the chamber; Let them fall until they reach terminal velocity. Using the microscope, measure the terminal velocity and use a formula to calculate the mass of each drop. 2. Apply a charge to the drops by filling the bottom chamber with x-rays. Electrons attach themselves to the oil drops and an electric voltage results from the battery. 3. If the voltage was just right, the force would make it balance the force of gravity and the drop would be suspended in mid air. 4. When a drop is placed, it’s weight mass and the acceleration due to gravity, is approximately equal to the electric force applied.

DATA COLLECTED  Rise and fall times of a single oil drop with calculated number of elementary charges on drop Tf Tr n 1/Tf 1/Tr n (1/n)(1/Tr 1/Tf) (1/n)(1/Tr 1/Tr ) 1/T

ANALYSIS AND CONCLUSIONS DRAWN  Millikan learned from this experiment what the charge of an electron was. He figured out how large or how small that charge was. He determined what the smallest unit of charge was and used the experiment to figure out the size of the charge of a single electron, instead of just a group of them.  He figured out that the charge on one of the drops was usually always a multiple of -1.6 X 10^-19C, even when doing the experiment and equations many times.  The number -1.6 X 10^-19C proved that the value was quantized(meaning that, that is the smallest your charge can go; it can be increased by a full step but never decreased by a half step) and that this was the charge of a single electron.

SOURCES        Modern Chemistry- Holt, Rinehart, and Winston