# a question about resistors in an arc experiment

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

1. ### S ClausGuest

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.

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 AllisonGuest

"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 ElseGuest

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. ### Archimedes' LeverGuest

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

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

5. ### Archimedes' LeverGuest

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

We just solved the energy crisis! Bwuahahahaha!

6. ### Phil AllisonGuest

"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

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

Then **** off.

...... Phil

7. ### Joe G \(Home\)Guest

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 ElseGuest

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. ### GreegorGuest

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

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...

10. ### krwGuest

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. ### MooseFETGuest

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. ### NobodyGuest

Or, more succinctly:

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

Negative resistance
(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. ### ehsjrGuest

I hate it when that happens.

14. ### Rich GriseGuest

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 GriseGuest

While it's blowing, yes.

Hope This Helps!
Rich

16. ### Rich GriseGuest

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 GriseGuest

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 GriseGuest

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. ### krwGuest

....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. ### krwGuest

Why, thank you! I love you too.