Re: LR demo circuit

[Wolfgang Rueckner <rueckner@FAS.HARVARD.EDU>]

Actually, inductors are available that allow for time constants of the
order of seconds.  These are iron-core type.  See, for example,

http://www.fas.harvard.edu/~scidemos/ElectricityMagnetism/OHPRLC/
OHPRLC.html

Switch bouncing time is indeed of the order micro to milliseconds, so
long LR time constants  will tend to "hide" the switching noise.  --
Wolfgang




On Jul 6, 2004, at 3:49 PM, Carl E. Mungan wrote:

> I would like to build an LR circuit. For RC circuits, it is
> relatively easy to get timescales on the order of seconds, which
> makes demos and measurements easy with simple meters. However, it
> doesn't seem to me to be quite so easy to do this for an LR circuit.
> A reasonably well-wound coil has an inductance of a few tenths of
> henries and a resistance of a few hundred ohms. Hence L/R is at least
> 3 orders of magnitude away from the seconds timescale and it seems it
> would take a pretty unusual coil to bridge this gap.
>
> So I'm willing to settle for having to using an oscilloscope to catch
> the action. But now my question is what kind of switch to use?
> Conservatively estimating an inductance of 0.1 H and a resistance of
> one kilo-ohm (to allow use of an external variable resistor that
> isn't dominated by the inductor's resistance), it seems to me that I
> need to be able to switch cleanly on the timescale of about 10
> microseconds. My experience suggests this is better than what
> ordinary mechanical switches can do, which are subject to electrical
> "bounces" upon contact. (I'm sure there's a technical name for this,
> but you probably know what I mean.)
>
> So what kind of switch should I use? Simple, readily available
> solutions preferred. Thanks, Carl
> --
> Carl E. Mungan, Asst. Prof. of Physics  410-293-6680 (O) -3729 (F)
>        U.S. Naval Academy, Stop 9C, Annapolis, MD 21402-5040
> mailto:mungan@usna.edu       http://usna.edu/Users/physics/mungan/