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Formula for electric field for capacitor and cylinder

  1. Feb 19, 2014 #1
    My prof gave two formulas without much explanation as to where he got them from. For a parallel plate capacitor he gave it as E=k2∏q/A and for a cylinder he gave E=kq2/Lr where L is the length of the cylinder and r is the radius and A is the area. Can someone please explain how he derived these.
  2. jcsd
  3. Feb 20, 2014 #2


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    hi derek181! :smile:

    he gets it from the electric displacement field, D, which is always equal to the surface charge density, ie charge/area …

    D = q/A or D = q/2πrL :wink:

    (and see here)
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