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Homework Help: Electric field problem!

  1. Jan 24, 2008 #1
    1. The problem statement, all variables and given/known data
    A small drop of water is suspended motionless in air by a uniform electric field that is directed upward and has a magnitude of 10800 N/C. The mass of the water drop is 3.99 x 10-9 kg. How many excess electrons or protons reside on the drop?

    2. Relevant equations
    which equation do i use? Do i need to use the mass of a proton to find the number of excess protons?

    3. The attempt at a solution

    F=ma; E=F/q
  2. jcsd
  3. Jan 24, 2008 #2
    The force from gravity acting on the rain drop, Fg=mg, will need to equal the force from the electric field, F=E*q, for the drop to stay motionless
  4. Jan 24, 2008 #3
    And how do I solve for how much protons are present?
  5. Jan 24, 2008 #4
    (Or electrons)

    Well you're gonna solve for q, so you'll know the NET charge on the raindrop. You know the charge of a SINGLE proton or electron
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