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a question about resistors in an arc experiment

Discussion in 'Electronic Design' started by S Claus, Jan 15, 2009.

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  1. S Claus

    S Claus Guest

    Hi all

    I was browsing through the book "Analog Circuit Design: Art, Science
    and Personalities" and checked on Chapter 8, titled "True Analog
    Circuit Design". On page 59 in this chapter, Tom Hornak writes about
    how he got involved in electronics when he was younger. He explains
    his and his friends first hands-on experiment which dealth with
    electric arcs as thus:
    We used a 1kW smoothing iron as a series resistor and large iron nails
    as electrodes.

    I had a dumb question about this, which is that what is the reason for
    using a resistor in this type of experiement? I mean, would there not
    be more current and therefore a larger arc if no resistor was used?
    How is the limiting of the current flow (by the resistor) desireable?
     
  2. Phil Allison

    Phil Allison Guest

    "S Claus"


    ** With no series resistor, the current flowing in the arc would become huge
    and blow the fuse or circuit breaker in the supply.




    ..... Phil
     
  3. Sylvia Else

    Sylvia Else Guest

    If they had negative resistance, they're be dissipating negative power.
    I think you mean that they have a negative resistance slope. They'll
    still have a positive resistance, and for a given applied potential,
    they'll conduct a defined current.

    Syvia.
     
  4. Bwuahahahahaha! I liked that one, John. :-]

    Tried to sneak it in there, I see...
     

  5. He's funny. I liked the impression his wording gave. :-]

    We just solved the energy crisis! Bwuahahahaha!
     
  6. Phil Allison

    Phil Allison Guest

    "Dan Coby"

    ** You are no judge of any such thing - asshole


    ** Sylvia is damn TROLL.


    ** Which is what he has said.

    " Most arcs have negative resistance, "


    ** See:

    http://en.wikipedia.org/wiki/Negative_resistance#Circuits_with_negative_differential_resistance

    Read the definition.

    " However, the use of the term negative resistance to encompass negative
    differential resistance is more common. "

    Then **** off.



    ...... Phil
     
  7. The other people who replied to you are correct.

    Current = Volts / resistance

    A short is resistance is near zero

    Thus Current = 120Volts / 0 = Infinite (huge current)

    Lets say the resistance in the power wires is 0.1 ohm

    then the current is = 120 / 0.1 = 1200Amp !

    Joe
     
  8. Sylvia Else

    Sylvia Else Guest

    He could simply have said that that was what he meant.

    Except that it wouldn't support his view that the current would increase
    without limit.

    Sylvia.
     
  9. Greegor

    Greegor Guest

    Nobody's mentioned the internal resistance in
    some types of power supplies.

    32 years ago (+-) I had a nice 30 KV 10 ma neon sign
    transformer that made a fabulous big Jacobs Ladder.

    40 years ago (+-) I scrounged 4 or 5 CASES (25 each)
    of discarded telephone company carbon zinc dry cells.

    I dissected a few that were beat up, extracting
    the large carbon rods, and wired many of the others
    in series. 40 volts seemed to work good to get
    a really good carbon arc between the naked rods.

    My main point is that batteries and transformers
    have an internal resistance.

    What kind of line isolation are you using
    and what are you trying to do with the arc?

    Safety warnings are not just obligatory in this case.
    Carbon arc presents blinding eye damage issues..
    Neon sign transformer presents deadly high voltage...
    Your first mistake would be your last.
     
  10. krw

    krw Guest

    He wasn't corrected, simply sniped. The term "negative
    resistance" is part of the jargon meaning "negative incremental
    resistance", understanding that a passive device cannot have a
    negative real resistance. ...but everyone here knows that.

    You love it on the _few_ occasions when you can dig at Larkin,
    don't you? ...but everyone knows that. Even DimBulb is with you
    on this snipe hunt.
     
  11. MooseFET

    MooseFET Guest

    I very much doubt that he actually thinks it is literally "without
    limit". A few hundred amps makes a very big mess of things.

    The voltage drop on an arc of constant length does decrease as the
    current increases. The rate of decrease slows at higher currents. At
    extremely high currents, the size of the plasma ball will suddenly
    decrease as will the voltage as a black hole is formed. This usually
    leads to the end of the universe.
     
  12. Nobody

    Nobody Guest

    Or, more succinctly:

    http://en.wikipedia.org/wiki/Negative_differential_resistance

    Negative resistance
    From Wikipedia, the free encyclopedia
    (Redirected from Negative differential resistance)
    He probably assumed that it was obvious. I've heard the term used
    occasionally (e.g. w.r.t. tunnel diodes or UJTs), and I've never seen
    anyone feel the need to add the "differential" or "slope" part.
    Sure it would (unless you genuinely believe that, by "without limit", he
    was claiming that the current would rise to infinity).

    For a constant supply voltage, positive resistance results in
    negative feedback and stable equilibrium, while negative resistance
    results in positive feedback and unstable equilibrium.
     
  13. ehsjr

    ehsjr Guest

    I hate it when that happens.
     
  14. Rich Grise

    Rich Grise Guest

    Then howcome it's been called "negative resistance" since as long as I
    can remember, but today is the first time I've ever heard the term
    "negative resistance slope"?

    Thanks,
    Rich
     
  15. Rich Grise

    Rich Grise Guest

    While it's blowing, yes.

    Hope This Helps!
    Rich
     
  16. Rich Grise

    Rich Grise Guest

    What argument? Negative resistance has been "negative resistance" since
    the invention of the arc.

    What planet have you been on for the last 100 or so years?

    Thanks,
    Rich
     
  17. Rich Grise

    Rich Grise Guest

    Why do you call this a "view"? The facts are, the arc will conduct as much
    current as the universe can supply. Maybe you mean "It wouldn't be
    'without limit' because the power plant would melt" or some such, but
    that's not a limitation of the arc.

    Quit being a PITA.

    Thanks,
    Rich
     
  18. Rich Grise

    Rich Grise Guest

    I made a carbon arc one time with "D" cell carbons, and Mom's iron
    in series. I just wired the whole iron in series, so when it got to
    the hottest setting, it turned itself off. Later, after I had moved out
    and bought my own iron, one of the guys in the dorm borrowed it,
    bypassed the thermostat, and melted my iron. )-;

    Cheers!
    Rich
     
  19. krw

    krw Guest

    ....except that he is not.
    Seems a bit of PKB going on here.
    Why not?
    Perhaps. It seems to be snipe season around these parts.

    When AlwaysWrong is "right", you'd better rethink your position.
     
  20. krw

    krw Guest

    Why, thank you! I love you too.
     
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