User:Dan C. Wilkinson/Notebook/Physics 307L/9/15/10

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Millikan Oildrop Experament


The goal of this lab is to determine the charge of the electron. We will do this by ballancing the forces felt by a small oil drop in the presence of an electric field. It's motion will let us determine an overall charge of the oil drop. Collecting a large amount of data will allow us to determine the charge of the electron (the smallest devisor of the collected data).


  • Pasco Millikan Oil Drop Apparatus, model AP-8210
  • Roberts Travel Size Mineral Oil Pressure Website
  • Smeic Micrometer
  • Wavetek TrueRMS 85XT


  • Distance Between Plates = (cm)
  • Density of Oil = (g/cm^3)
  • Acceleration of Gravity = (cm/s^2)
  • Viscosity of Air in Poise = (dynes/cm^2)
  • Barametric Pressure = 29.80in [1] (cm Mercury)
  • b–constant, equal to 6. 17 x l0-4 (cm of Hg) (cm)
  • Voltage Accross Plates = 499.5 (V)
  • Ristance of Thermistor = 2.177Mohm (3:24pm), 1.987Mohm (4:38)


  • Plug in Halogen light source to wall power supply
  • Remove plastic cover and black plastic piece and inserted focusing pin
  • Look through eyepiece and focus on the pin and the grid (the further adjustment knob brings the pin into focus and the closer knob brings the grid into focus.
  • Pluged in the DC power source and used the above mentioned multimeter to adjust the voltage to 499.5V.
  • Used the multimeter to measure the resistence of the thermistor getting 2.177Mohm, will check this resistence periodically (especially when making measurments) to ensure that the temperature is known.
  • We had to adjust the halogen lamp settings using the horizontal and vertical knobs on the light source. We noticed that moving these knobs changed the focus area of the oil drops. For example, at first the oil drops could only be seen on the left hand side. After some alignment we were able to move the plane of focus to the center of the grid.


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