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Parallel Plate Capacitor Diameter

  1. Jan 27, 2014 #1
    1. The problem statement, all variables and given/known data

    Two circular disks spaced 0.50 mm apart form a parallel-plate capacitor. Transferring 1.70 ×109 electrons from one disk to the other causes the electric field strength to be 3.50 ×105N/C.

    What are the diameters of the disks?

    2. Relevant equations

    Refer to attachment

    3. The attempt at a solution

    So I substitute everything into the formula and end up getting R = .5 mm. I then double this to find the diameter and still get the wrong answer. Any ideas?

    Attached Files:

  2. jcsd
  3. Jan 27, 2014 #2


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    Staff: Mentor

    Not sure what you're intending to do with that equation you attached. It looks like the on-axis field for a charged circular disk at some distance z from the disk along the axis. But here you have a parallel plate capacitor and the field will be (essentially) uniform between the parallel plates.

    Look instead to formulas related to parallel plate capacitors.
  4. Jan 27, 2014 #3


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    Homework Helper

    convert Q to Coulombs, then use Gauss to obtain Area.
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