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Does every object have capacitance?

  1. Oct 18, 2009 #1
    Does every object have a capacitance associated with it? For example, is there a capacitance in a single wire or a chair? If so, can you please explain why because I was taught that capacitance is associated with two conducting objects. Thank you.
     
  2. jcsd
  3. Oct 18, 2009 #2
    If an object can be charged then it has capacitance defined by the equation C=Q/V.Here Q is the charge and V the potential.Capacitance is usually associated with two conducting objects in close proximity because the capacitance of isolated objects is extremely small.
     
  4. Oct 19, 2009 #3
    My understanding is:
    capacitance is the ability to hold an electric potential differant than the electic potential of objects near it.
    In that case, all objects have the potential to have capacitance, they just need to either; a) be non-conductive or b) be electrically issolated from the other object.
    Items that are non-conductive (relatively) still bleed charge, just a lot slower, so the differance is noticable.
    Take a CRT screen. The electron beam coming from the back charges the screen (glass) makign a noticable field. It feels a little like fur. If a little fabric softner is sprayed on the CRT, that field disipates.
    The same thing happens with cloths.
    Humid air can conduct charges easier than dry air. This is the reason you can shock people with static electicity easier in the winter. Heating air reduces its humidity meaning it takes longer for a static charge to disipate. The discharge when you zap someone is the equalizing of capacitance.

    Another way of saying this is:
    Capacitance is the measure of how much electrical potential differance an object can hold in reference to another object.
    This applies to all objects.

    You see capacitance discussed in conductors more often because that is where capacitance causes the most problems. Conductors will induce a charge in another conductor this induced charge can cause problems if not planned for or can be used if planned for.
     
  5. Oct 19, 2009 #4
    The capacitance between two concentric conducting shells of radius b and a, b>a, is

    C = 4 pi e0 ab/(b-a)

    so the capacitance of a 5-cm radius sphere in a 5 meter radius room (with grounded plumbing, wires, etc in the walls) is about 5.5 picofarads. So everything does have some capacitance to something.
    Bob S
     
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