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Homework Help: Finite Sheets

  1. Jan 24, 2010 #1
    1. The problem statement, all variables and given/known data

    Consider two thin disks, of negligible thickness, of radius R oriented perpendicular to the x axis such that the x axis runs through the center of each disk. The disk centered at x=0 has positive charge density n, and the disk centered at x=a has negative charge density -n , where the charge density is charge per unit area. What is the magnitude E of the electric field at the point on the x axis with x coordinate a/2?
    Express your answer in terms of n, R, a, and the permittivity of free space Epsilon0

    2. Relevant equations



    3. The attempt at a solution
    Since I can't type this out with proper math code legibly (or at least i don't know how to), I uploaded a picture of the sheet I did my work on. Please let me know where i went wrong! I also uploaded a pic of the problem so you can visualize it. Thank you!
     

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  2. jcsd
  3. Jan 24, 2010 #2
    i think that is what i did in my work??
     
  4. Jan 24, 2010 #3

    vela

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    One mistake is in your calculations is that you used n as the total charge on the disk. You didn't need to do that because n is the charge density; it's what you called [itex]\sigma[/itex].

    Also, check your integration. You didn't show any steps, so I can't tell what you did wrong.
     
  5. Jan 24, 2010 #4

    vela

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    Actually, I think your integration is correct, so it's just the other mistake. Everything else looks okay to me.
     
  6. Jan 24, 2010 #5
    OOOHHH THANK YOU...yea i definitely thought n was the charge, not the charge desnity....got the answer correct when i fixed that....9 times out of 10, i usually just read the problem wrong! HAHA

    thanks again! :)
     
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