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Homework Help: EM: accelerated charge and E field

  1. Apr 7, 2006 #1
    An electron is initially at rest. At a time t1 = 0 it is accerated upward with an acceleration of 10^18 m/s^2 for a very short time (this large acceleration is possible because the electron has a very small mass). We make observations at a point A, which is 15 meters to the right of the electron's initial position.

    a. At time t2 = 1 ns, what is the magnitude and direction of the electric field at point A?
    b. At what time t3 will the electric field at location A change?
    c. What is the direction of the radiative electric field at location A at time t3?
    d. What is the magnitude of this radiative electric field?
    e. Just after time t3, what is the direction of the magnetic force on a positive charge that was initially at rest at location A? Explain with a diagram.

    I need equations for (a) and (b) at least. Thanks.
  2. jcsd
  3. Apr 7, 2006 #2


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    Acceleration is the second derivative of position (spatial) with respect to time. So determine the position at 1 ns for part a. One finds the position of the electron 1 ns after being accelerated, and from that one determines the electric field due to the electron at 15 m to the right (pt A) from where the electron started at t=0. The problem does not state anything about an applied electric field, which is basically how one accelerates charges.

    Part b, is asking simply how long does the influence of the change in the electron's position take to reach point A. Think of t = distance/velocity.
  4. Apr 27, 2010 #3
    Okay, it has been forever since calc for me so to determine position.... what do I do?
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