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Homework Help: Electron's Speed in Field and Charge

  1. Jan 21, 2007 #1
    1. The problem statement, all variables and given/known data

    An electron is released from rest in a uniform electric field of 1.25 kN/C. After 20 ns, the electron's speed will be approximately


    a. 2.5 x 10^-5 m/s

    b. 3.9 x 10^3 m/s

    c. 3.0 x 10^8 m/s

    d. 2.5 x 10^3 m/s

    e. 4.4 x 10^6 m/s




    2. Relevant equations

    Vector E = (m_e*a)/q_e

    v_f = v_i +a*t


    3. The attempt at a solution

    a = (E*q_e)/m_e = [(1250 N/C)*(1.60*10^-19 C)]/(9.11*10^-31 kg) = 2.1954*10^14 m/s^2

    v_f = v_i +a*t, where v_i = 0 m/s

    v_f = a*t = (20*10^-9 s)*(2.1954*10^14 m/s^2) = 4.39*10^6 m/s (E.) ???



    1. The problem statement, all variables and given/known data

    How many electrons must be transferred to a body to produce a charge of 125 nC?

    a. 1.25 10^-7
    b. 7.81 10^11
    c. 1.28 10^12
    d. 3.45 10^11



    2. Relevant equations

    Total q / q_e = # of electrons

    3. The attempt at a solution

    (125*10^-9 C)/(1.60*10^-19 C) = 7.813*10^11 electrons ???

    Thanks.
     
  2. jcsd
  3. Jan 21, 2007 #2

    Kurdt

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    Staff Emeritus
    Science Advisor
    Gold Member

    Both correct as far as I can see.
     
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