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!

Electrostatics and infinately charged plate question driving me nuts!

  1. Apr 10, 2009 #1
    1. The problem statement, all variables and given/known data
    An electron is released from rest 2.0 cm from an infinite charged plane. It accelerates toward the plane and collides with a speed of 1.0x10^7m/s. What is the surface charge density of the plane?The answer is 2.52×10−7 C/m^2 !


    2. Relevant equations
    v=d/t, d=0.5at^2, E=n/2*8.85x10^-12, F=ma=Eq


    3. The attempt at a solution
    I don't know what to do with the velocity. I tried relating it to energy but got stuck.
     
  2. jcsd
  3. Apr 10, 2009 #2

    Doc Al

    User Avatar

    Staff: Mentor

    Use that and the distance to find the electron's acceleration.
     
  4. Apr 10, 2009 #3
    using v=d/t t is 2E-9
    using a=v/t a is 5E15
    E=ma/q E=28469
    E=n/(2 epsilon not).. n=5.03E-7

    which is 2 times too big, but isn't E=n/(2 epsilon not) the correct equation, with the 2?
     
  5. Apr 10, 2009 #4

    Doc Al

    User Avatar

    Staff: Mentor

    That equation applies for constant velocity, not accelerated motion. But you can use it if you replace v (the final velocity) with the average velocity. What's the average velocity?

    You can also make use of additional kinematic relationships.
     
  6. Apr 10, 2009 #5
    ahh so I guess you mean Vf^2=V0^2 + 2ad because that works haha

    Thanks!
     
  7. Apr 10, 2009 #6

    Doc Al

    User Avatar

    Staff: Mentor

    That's the one. :wink:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Electrostatics and infinately charged plate question driving me nuts!
Loading...