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Homework Help: Minmum Voltage

  1. Jul 19, 2006 #1
    Suppose that after walking across a carpeted floor you reach for a doorknob, and just before you touch it a spark jumps 0.2 cm between your finger and the doorknob. Find the minimum voltage difference betwen your finger and the doorknob for this to occur.

    I did V=Ed

    which I plugged in (8.85 x 10^-12)(.2 x 10^-3) and I got this wrong. What am I doing wrong?
  2. jcsd
  3. Jul 19, 2006 #2

    Andrew Mason

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    How are you determining what E is? It seems to be several orders of magnitude out. I think the breakdown E for air is in the order of a few million volts/metre. Also you appear to be using .2 mm not .2 cm.

  4. Jul 20, 2006 #3
    so it would be ((8.85 x 10^-12)/1.00059) x (2.2 x 10^-2) which is 1.769e-14?
  5. Jul 20, 2006 #4
    nevermind, i got it. i was using the wrong E, E was 3,000,000
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