maximazing capacitance

Discussion in 'General Electronics Chat' started by antennaboy, Dec 5, 2009.

  1. antennaboy

    Thread Starter Active Member

    Jan 31, 2008
    Hello Forum,

    I have two questions to pose:

    1) for a metallic object, it depends on its shape. If I had a sphere of surface area A1, its capacitance C1, in cgs, is equal to its radius R.
    If I could change the shape of the sphere, while maintaining the same
    surface area, A2=A1, what shape would I turn the sphere into to
    increase its capacitance C2? Would I want to create spacing, corners?

    A single conductor has its own capacitance which is the ability, for a
    given voltage difference applied to it, to store electric charge. The
    fact that we always see two conductors is because the presence of the
    second conductor makes the capacitance of the first conductor
    increase. Is that correct?
    What if we had a parallel plate capacitor made of two plates with
    different surface area :A1>A2.
    Would the capacitor have the same, bigger, smaller capacitance than
    the case where A1=A2?

    2) Inductance: for what I know, inductance is a geometrical factor too
    that L expresses amount of the resistance (reactance) to time
    changes in current. The faster the current change and the bigger L,
    the bigger the resistance (reactance).

    How can we have an inductor with infinite inductance?
    What does it mean "zero reluctance to the magnetic flux"?

  2. Paulo540


    Nov 23, 2009
  3. rjenkins

    AAC Fanatic!

    Nov 6, 2005

    For a SINGLE conductor, what are you measuring the voltage DIFFERENCE to?
    Something of a paradox here...

    You cannot have a Difference without two points of reference.
  4. antennaboy

    Thread Starter Active Member

    Jan 31, 2008
    The other point is at infinity where V(infinity)=0.....
  5. davebee

    Well-Known Member

    Oct 22, 2008
    You're both right -

    There are two somewhat different applications of the term "voltage". From a practical point of view, voltage is what is measured when voltmeter probes are stuck into a circuit to measure the voltage difference between two points.

    But then there is the physicists point of view, where voltage is the energy necessary to bring a charge from an infinite distance to some point in space which may be in some electric field. This is called electric or electrostatic potential, but it is measured in the same volts that are measured in a circuit.

    I would guess that the sphere would present the greatest capacitance, because any deviation from the sphere would require that the remaining material would have to be of a shape that would approximate a sphere of less diameter.