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Minimum amount of charge required?

Discussion in 'Electronics Homework Help' started by error404, Sep 2, 2012.

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  1. error404

    error404

    3
    0
    Sep 2, 2012
    Hello,

    I've been looking online for an answer to this question but didn't find any yet. hope you guys can help.

    If I had 2 point charges, X and Y spaced by 1 Meter of air. what are the minimum values for X and Y that could form a spark between the 2 charges?
    I saw online that the breakdown value for air was 30 Kv/cm or something like that but i have no clue how to convert this value into charges in coulombs! :confused:

    Is there any formula that can predict the values for X and Y in such a case?

    Thanks,
    Error404
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    There are just so many variables.

    For example, air pressure, temperature, humidity, composition of atmosphere.. they all make a difference.

    Then you have the nature of the charges. Are they charged spheres, or point charges. The smaller the object with the charge, the more readily it ionises nearby atoms.

    This is 206, I suggest you 303 to google.
     
  3. wingnut

    wingnut

    242
    9
    Aug 9, 2012
    My best shot is this

    V= kQ1/r

    For two point charges just add them
    Vt = kX/1 + kY/1 remembering the sign of each charge

    If breakdown in air is as you say 30kV/cm that means Vt= 30kV x 100 as there are 100cm in a m. Vt = 30 000 00 V

    Therefore 3000000 = kX/1 + kY/1 where k = 9 x 10^9

    The above may be wrong but is my best shot
     
  4. error404

    error404

    3
    0
    Sep 2, 2012
    Great info, thanks mate.
    can i know the name of this formula u just used?

    Error404
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Since you're not interested in practicalities, I can only assume this is homework.
     
  6. CocaCola

    CocaCola

    3,635
    5
    Apr 7, 2012
    Cute :D
     
  7. davenn

    davenn Moderator

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    Sep 5, 2009
    have to admit that one went over my head :rolleyes:

    Dave
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    404 is a return code, as are 206 and 303

    200!
     
  9. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    I'll have to remember that :)
     
  10. error404

    error404

    3
    0
    Sep 2, 2012
    Mr.Steve
    Thanks for your reply, sorry I couldn't reply you on time.
    These variables actually contribute to a change in the answer to my question, that's why I was looking for some rule to take as much variables as possible into account. (does such a formula exist?)
    They are point charges, as I have assumed in my question.
    I am not looking for a sharply correct value, but the closest indication of how much charge is required.

    Sorry to disappoint you, but this is not a homework :)

    Error404
     
  11. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Well, if it's not a homework question then they're not point charges.

    Why not try describing your actual problem rather than making up a theoretical question?

    Point charges tend to leak away by themselves. Especially if they are truly mathematical points.

    See here.
     
  12. Harald Kapp

    Harald Kapp Moderator Moderator

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    Nov 17, 2011
    Whatever:
    Asking for the absolute value of the charges makes no sense. Both charges can be arbitrarily high (or low) without any spark as long as the potential difference (also know to insiders as "voltage") is below the breakdown voltage of the medium.
    What you're looking for is the voltage or potential difference and therefore the difference in charge between points X and Y.
     
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