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Magnitude of electric force on a proton

  1. Jun 13, 2015 #1
    1. The problem statement, all variables and given/known data
    Two protons are 2.5fm apart.
    What is the magnitude of the electric force on one proton due to the other proton?

    2. Relevant equations
    Fe = K|q1||q2| / r2

    3. The attempt at a solution
    Fe = (9 x 109)x(1.6 x 10-19)2 / (2.5 x 10-15)2
    Fe = 37 N

    I got the answer but I don't understand why I am able to use e= 1.6 x 10-19 as q1 and q2? could someone explain? thanks
     
  2. jcsd
  3. Jun 13, 2015 #2

    Orodruin

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    Because both protons have this charge.
     
  4. Jun 13, 2015 #3

    rude man

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    You have two charges:
    q1 = 1.6e-19C
    q2 = 1.6e-19C
    why wouldn't the formula F = kq1q2/r2 apply here?
     
  5. Jun 13, 2015 #4
    Wait, I'm confused.. isnt 1.6 x 10^-19 the charge of an electron?! Oh wait, is it because charge of electron = charge of proton if its neutral?
     
  6. Jun 13, 2015 #5

    Orodruin

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    +1.6 x 10^-19 C is the charge of a proton. -1.6 x 10^-19 C is the charge of an electron. They are the same magnitude but of opposite sign. Also note that the unit is important, 1.6 x 10^-19 is not a charge, it is a number.
     
  7. Jun 13, 2015 #6
    Thank you so much, that cleared things up :)
     
  8. Jun 13, 2015 #7

    rude man

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    Charge of electron = -charge of proton. The thing that's neutral is the atom, comprising electrons, equal number of protons yielding the "neutrality", plus possibly neutrons which have no charge. ( The exception is ions which do have a net charge. Example: add salt to water, you get mostly sodium and chlorine ions).
     
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