Re: Measuring amps on 9 volt battery

From: Peter Bennett (peterbb_at_somewhere.invalid)
Date: 11/04/04 

Date: Wed, 03 Nov 2004 18:10:52 -0800

On Wed, 03 Nov 2004 17:29:41 -0600, John Fields
<jfields@austininstruments.com> wrote:

>R2 and R3 are in parallel, and to determine the total resistance of
>the pair we can write:
>
>
>
> R2 * R3
> Rt = ---------
> R2 + R3
>
>
>Where Rt is the total resistance of the pair.
>
>
>For your digital multimeter, with a 10M input resistance we'll get:
>
>
>
> R2 * R3 20 * 10E6
> Rt = --------- = ---------- = 19 999 960 ohms
> R2 + R3 20 + 10e6

Watch those pesky periods! That should be 19.999 960 ohms
>
>
>and for the 20,000 ohms-per-volt analog multimeter we'll get
>
>
> R2 * R3 20 * 200000
> Rt = --------- = ------------- = 19 998 000 ohms
> R2 + R3 20 + 200000

And that is 19.998 000 ohms - both such a tiny bit under 20 ohms, that
we may as well call it 20 ohms. 

-- 
Peter Bennett, VE7CEI  
peterbb4 (at) interchange.ubc.ca  
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca