Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Elementary Charge lab question?

  1. Sep 22, 2011 #1
    I need to design a procedure for this lab.

    I measured the mass of a couple of bags containing the same object in random amounts. Without looking at how many objects are in the bag i have to determine the mass of one object.

    At first i thought that since each mass measured should be a multiple of the mass of one object, dividing any two of the masses will give a ration of numbers. The numerator and denominator represent integers that will help determine the mass of an individual object.
    The teacher said it had to do something with formulas that concern gravity and force. Another group tried to use density and volume formula to solve it. I'm pretty stuck here, can anybody please help me??
  2. jcsd
  3. Sep 22, 2011 #2


    User Avatar
    Homework Helper

    I disagree with "formulas that concern gravity and force" so I may be on the wrong track here. It seems to me you are doing a lab to familiarize yourself with the methods used by Millikan to find the elementary charge. AFTER he measured all those charges, how did he get an estimate of the elementary charge? Just analyzing numbers, no physics formulas.

    I suggest you check out this pdf on the Millikan experiment.
    The whole thing is interesting, though the bit on viscosity may well be beyond your present physics level. The very last section with the title "So you’ve at last got the charges on a bunch of different drops. Now what?" is exactly what you need.

    Many people can "see it" more easily on a graph. Take a full sheet of graph paper with mass on the side (beginning at zero) and the bag number on the bottom and plot all your data. Look only at the lower part of the graph at first. Look for clusters of dots along horizontal lines. Each line should be at a mass that is a multiple of some basic mass (at a level where there may be no dots). That basic mass is what you are looking for.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook