lab4_millikan - PHY 252 Lab 4: Millikan oil drop/charge of...

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PHY 252 Lab 4: Millikan oil drop/charge of electron Fall 2009, version 2 The purpose of this experiment is to measure the smallest unit into which electric charge can be divided, that is, the charge e of an electron. The method is essentially the one employed by R.A. Millikan in 1910. The essence of the experiment is to measure the terminal velocity of a falling droplet to measure its radius r and thus mass m , and then to suspend the droplet with an electric field so that one can measure its charge q from qE = mg . By repeating many measure- ments, Millikan was able to show that charge comes in integer multiples of a fundamental value. Millikin used oil droplets for his experiments; you’ll use micrometer-scale polystyrene spheres instead. When objects move through a fluid, one can have either turbulent or laminar flow. The dividing line between the two is given by the Reynolds number R = ρvL/η , which is the ratio of inertial to viscuous forces found from the fluid density ρ , dynamic viscosity η (some books use μ to represent this), velocity v , and characteristic length L of the object moving through the fluid. Low Reynolds number ( R < 30 ) corresponds to laminar flow, while high Reynolds number ( R > 3000 ) corresponds to turbulent flow. In the low Reynolds number limit (appropriate for micrometer-scale objects moving through air), the drag forces on a sphere with radius r is given by
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This note was uploaded on 05/28/2011 for the course PHY 251 taught by Professor Rijssenbeek during the Fall '01 term at SUNY Stony Brook.

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lab4_millikan - PHY 252 Lab 4: Millikan oil drop/charge of...

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