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Determining the mass and electric charge of the falling fluid drops.

- The terminal velocity of a fluid drop falling in air in an
electric field is determined by its radius, charge and mass.

- Since the density of our test fluid is known we need to determine
only the charge and mass.

- By taking measurements of the terminal velocity of the same fluid
drop with two different E field values, two equations can be obtained
to solve for the values of the drop's charge and mass.

- The charge measurement accuracy is limited in our apparatus by
Brownian motion. For 6 micron diameter drops a measurement accuracy of
1/100 e has been obtained.

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October 13, 1998

Stanford Linear Accelerator Center

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