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Some questions regarding capacitors

  1. Nov 18, 2015 #1
    1)The charge on the positive plate of a capacitor is called the charge on the capacitor.Why?
    I think it is just a convention.
    2)There is a passage in my textbook.
    Any conducting object that carries a charge is characterized by an electric potential that is constant everywhere on and within that object. If two such conductors have a potential difference between them then as any potential difference is able to accelerate charges,the system effectively stores energy
    I want to know what is the relation between acceleration of charge and storing energy
    My understanding:An easy way to accelerate a charge is to allow it to move through a potential difference. For example, if we take a charge and place it inside a parallel-plate capacitor.A positive charge released from (near) the positive plate will accelerate towards the negative plate. Cutting a hole in the negative plate allows it to escape. Similarly, a negative charge released from near the negative plate will accelerate across the gap and leave the parallel plates at high speed.Is energy produced by acceleration of charge something about electron volt
    :a unit of energy equal to the work done on an electron in accelerating it through a potential difference of one volt.
    If yes,how it is stored?
    3)Any arrangement of two isolated conductors carrying equal and opposite charges can be called as capacitor.The two conductors can be spherical,cylindrical ,or plane sheets.My question is what if one conductor is spherical and the other spherical,I mean can isolated conductors of two different shape/geometry form a capacitor?
    I think yes as long as both of them equal and opposite charges.
    4)Is earthing necessary to form parallel plate capacitors?
  2. jcsd
  3. Nov 18, 2015 #2


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    Yes. The other plate has the opposite charge.
    Yes. An example: You are one plate of a capacitor with the earth as the opposite plate.
    No. Capacitors are often used to block DC and let AC signals through. Neither plate is grounded.
  4. Nov 19, 2015 #3
    I think no. The sentence of the charges equation is the ascertaining of the principle symmetrical charge of the capacitor. This is explained by the fact that the capacitor is charged by interacting with the external body as a single entity and to charge it asymmetrically is quite difficult. To be honest it can be realized, but the theory describes the only symmetrically charged capacitor unless otherwise stated . When I learn that, the capasitor was just "two conductors divided by the layer of dielectric" and the principle of the charge symmetry was negotiated separately as a constraint for the model. At present the capacitor is defined as "two symmetricaly charged conductors divided by the layer of dielectric". The advantage is that nothing more is needed to negotiate. The disadvantage is that the object has become dependent on the process.
    To create (the accelerating) potential difference, it must be first accumulated opposite charges.. To do this, the work must be done. So there is an accumulation of energy.
    Heh... In techic, - yes. But in physics capacitor is an abstraction. It has no an active resistance and resistance of inductance, and this means that the shape of the conductors can not be absolutely independent (or arbitrary) one from each other. But in a real world all whatever you see is a capasitor or its part. :D
    Last edited: Nov 19, 2015
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