Re: Gap Question

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "S & J Young" <youngs-at-konnections-dot-net> 

There are many.  An ordinary incandescent light bulb is one example.  If you
series connect a 40 watt bulb along with the right combination of inductor
and capacitor so that the RLC combination is very close to 60 Hz (in the
USA), the bulb will oscillate from bright to dim indefinitely at a rate
determined by the thermal constant of the bulb.  Why?  Because the nonlinear
R of the bulb causes the circuit to go in and out of 60 Hz resonance.

An ordinary diode is another example.  An iron core inductor has a nonlinear
AC resistance (impedance) because the core starts saturating at higher
magnetic fields.  In fact, most active electronic components exhibit
non-linear effects.  That is why designers go to great lengths to apply
negative feedback and other compensation techniques to make the device
behave in a linear manner (e.g. your stereo amplifier has these techniques
applied so the output is a faithful amplified copy of the input.)

Anything with friction is another.  The resistance to a force applied is
non-linear when an object goes from static to moving when pushed
horizontally along a surface (coefficient of friction is non-linear because
of "sticksion").  E.g. your auto braking (deceleration) is better when the
tires don't skid on the road.  (A husband's resistance to a nagging wife is
usually non-linear - the so-called "breaking point" effect is highly
non-linear!)  The world is full of non-linear effects and devices.


----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Thursday, February 26, 2004 11:15 PM
Subject: RE: Gap Question


 > Original poster: "Luke" <Bluu-at-cox-dot-net>
 >
 > Can anyone point me to a device that does not have a linear resistance
 > but yet does not display a negative resistance?
 > Is there such an animal?
 >
 > Thanx
 >
 > Luke Galyan
 > Bluu-at-cox-dot-net
 > http://members.cox-dot-net/bluu
 >
 > -----Original Message-----
 > From: Tesla list [mailto:tesla-at-pupman-dot-com]
 > Sent: Thursday, February 26, 2004 5:34 PM
 > To: tesla-at-pupman-dot-com
 > Subject: RE: Gap Question
 >
 > Original poster: "Luke" <Bluu-at-cox-dot-net>
 >
 > Ok I see what you are saying.
 > Thanx
 > This is starting to click a bit.
 >
 > This has been a very enlightening topic for me!!
 >
 > I was used to thinking of resistance as something the hinders the flow
 > of electricity.  I know that is what it normally means.  But I was not
 > used to the term being made to refer to the V I properties and not
 > thought of as actual resistance per say.
 >
 > And yup I see what you mean in the lower graph the resistance decreases
 > but the slope does not go negative.
 >
 > So as well as learning some other stuff here I finally came to grips
 > with the word resistance in the term negative resistance is not
 > referring to actual resistance even though the V I can be used to
 > calculate a resistance.
 >
 > Thanx.
 >
 > Luke Galyan
 > Bluu-at-cox-dot-net
 > http://members.cox-dot-net/bluu
 >
 > -----Original Message-----
 > From: Tesla list [mailto:tesla-at-pupman-dot-com]
 > Sent: Thursday, February 26, 2004 7:19 AM
 > To: tesla-at-pupman-dot-com
 > Subject: Re: Gap Question
 >
 > Original poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br>
 >
 > Tesla list wrote:
 >
 >    > Is it safe to say that a device that displays negative resistance,
 >    > refers to a components ohmic value decreasing when there is an
 > increase
 >    > of voltage or current?  And yes I realize that this would only occur
 > at
 >    > certain areas on the V I curve.
 >
 > Use a fixed-width font to see the pictures.
 > Negative resistance occurs when the voltage decreases and the current
 > increases, or when the slope of the i x v curve is negative.
 >
 > |i         /      |i                /
 > |         /       |                /
 > |        /        |               /
 > |        \        |              /
 > |         \ here  |      here   /
 > |          \      |    /\      /
 > |        __/      |   /  \    /
 > |     __/         |  /    \  /
 > |  __/            | /      \/
 > |_/          v    |/                  v
 > +-------------    +--------------------
 >
 > It's not safe to define as Ohmic value i/v. In the negative resistance
 > region of the curves above it decreases as the voltage decreases, but
 > it does the same in the curve below, that doesn't have a negative
 > resistance area:
 >
 > |i              /
 > |              /
 > |             /
 > |    ________/
 > |   /
 > |  /
 > | /
 > |/                v
 > +------------------
 >
 > So, reserve the term "resistance" for linear resistors, or to measure
 > the slope of the i x v curve.
 >
 > Antonio Carlos M. de Queiroz
 >
 >
 >