38_millikan - Lesson 38: Millikan's Oil Drop Experiment The...

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Lesson 38: Millikan's Oil Drop Experiment The work of people like J.J. Thomson allowed us to find out about the existence of negatively charged electrons. In 1909 Robert A. Millikan came up with an experiment to measure the charge on an electron, called the Oil Drop Experiment . The apparatus was actually quite simple… There were two parallel plates set at a specific distance apart with a known voltage between them. That way we know the electric field strength. The top plate is positive, and the bottom plate is negative. Millikan drilled a very small hole in the center of the top plate. He then used an atomizer to spray very fine drops of mineral oil mineral oil over the top plate. An atomizer is like those fancy perfume bottles you see that have a ball you squeeze to make the perfume spray out. Friction between the nozzle of the atomizer and the mineral oil droplets caused some of the drops to gain a small charge (charging by friction). Just by chance, some of the oil drops might fall down the hole in the top plate. If they have a positive charge, we expect them to go accelerating
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38_millikan - Lesson 38: Millikan's Oil Drop Experiment The...

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