1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Periodic motion, electric charge

  1. Feb 20, 2008 #1

    tony873004

    User Avatar
    Science Advisor
    Gold Member

    Three parallel, infinite, uniformly charged planes are arranged as shown in Figure 24.32.
    (it looks just like it's described. The middle plate is positive sigma, the outer plates are both negative sigma.)


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

    A small hole passes through the middle plane. At t=0 an electron emerges from the hole moving perpendicular to the planes with speed vo . Assuming vo is small enough that the electron does not collide with the negative plate, show that its motion is periodic, and find the period.


    2. Relevant equations



    3. The attempt at a solution

    It's obvious that it will be periodic since there is no force to pull it off the x-axis, and there is no friction to rob it of energy.

    I have a feeling it's like a pendulum, where the amplitude does not affect the period. But we haven't had any examples of periodic motion yet in E&M.

    From the pendulum, we have a small amplitude formula for period of T=2pi sqrt(L/g). I imagine charge is somewhat analogus to gravity, and perhaps distance between the plates is somewhat analgous to L (length of pendulum). Where do I begin?



    2. Relevant equations



    3. The attempt at a solution
    1. The problem statement, all variables and given/known data



    2. Relevant equations



    3. The attempt at a solution
     
  2. jcsd
  3. Feb 20, 2008 #2

    rl.bhat

    User Avatar
    Homework Helper

    Using Gauss's theorem calculate the electric field between the plates. Then find force and acceleration of the electron. In SHM, acceleration = w^2.A, where A is the amplitude of SHM and that is the distance between the plates. From w you can find the period of the SHM.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?