Re: emf, potential, voltage

[brian whatcott <inet@INTELLISYS.NET>]

At 11:40 3/18/01 -0500, John Denker wrote:

> At 09:53 AM 3/18/01 -0600, brian whatcott wrote:
> > A resistor is a resistor when it is hot.
> ....
> > an oscilloscope shows the noise emf satisfactorily.
>
> I wish I had an oscilloscope as nice as Brian's.
>
> Let us assume
>         R = 1 meg
>         BW = 200 MHz
>
> When I do the calculations, it seems
>  -- a cool (300K) resistor has 0.91 mV RMS thermal noise, while
>  -- a hot  (400K) resistor has 1.05 mV RMS thermal noise.
>
> It takes a verrry fine oscilloscope to see that ... rather better than your
> garden-variety classroom scope.

Let me know how fine an oscilloscope it takes when you use the blow torch
I specified in my initial post. My scope cost me $50 (used).
 You might need to put out a dollar or two for the ceramic resistor too....


I guess it just takes a little persistance to dislodge these
 misapprehensions about 'emfs not applying to resistors' from a physicists'
 stock of 'givens'?       :-)





brian whatcott <inet@intellisys.net>  Altus OK
                Eureka!