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Coulomb's Law & Electrons

  1. Mar 2, 2009 #1
    1. The problem statement, all variables and given/known data

    Two spherical objects are separated by a distance of 1.98 x 10-3 m. The objects are initially electrically neutral and are very small compared to the distance between them. Each object acquires the same negative charge due to the addition of electrons. As a result, each object experiences an electrostatic force that has a magnitude of 4.19 x 10-21 N. How many electrons did it take to produce the charge on one of the objects?

    2. Relevant equations

    F = k q1q2/r^2

    N= Q/e

    k = 8.99E9 nm^2/c^2
    e= -1.602E-19C

    3. The attempt at a solution

    I used coulomb's law and plugged in the Force as 4.19E-21N, boltsmans constant for k and 1.98E-3m as the r^2.

    4.19E-21N = (8.99E9Nm^2/C^2)(q^2)/(1.98E-3)^2
    1.642E-26N/m^2 = (8.99E9Nm^2/C^2)(q^2)
    q = sqrt(1.82719E-36)
    q= 1.3517E-18C

    N= Q/e
    N= (-1.3517E-18C)/(-1.602E-19C)
    N= 8.43781 electrons

    I've done this over and over and get the same answer but it tells me i'm wrong and i'm not sure what else to try :/
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Mar 2, 2009 #2


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    Homework Helper

    I got the same thing independently. Looks like there is an error in the question.
  4. Mar 2, 2009 #3
    Thanks for your help, It's good to know I'm not crazy hah
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