[ot] use of a long coaxial cable

[Alma J Wetzker]

Ric Moore wrote:
> On Sun, 2007-01-21 at 06:53 -0500, David Bandel wrote:
>> On 1/21/07, Ric Moore <wayward4now at gmail.com> wrote:
>>> On Sat, 2007-01-20 at 20:38 +0800, Man-wai CHANG wrote:
>>>>> 10base2 is 50 Ohm.. period.
>>>>> 75 Ohm is probably (cable) TV or radio.
>>>> Do we need special equipment to measure impedance? I have forgotten my
>>>> A-Level physics... :)
>>> Just an Ohm meter...
>>>
>>> E = I times R
>>> Energy = Impedence times Resistance  which translates to:
>>> Volts = Amperage times Ohms.
>>>
>>> I've always wondered why they changed all the words?? Who and When?
>>>
>> They may have changed some of the words at some point, but resistance
>> and impedance are not the same.  Resistance is static.  Impedance,
>> however, is not static, it changes depending on frequency.  You don't
>> just measure impedance with an ohm meter.  Consider yourself gonged.
>> Show's over for you.  Please leave the planet.  Resistance is futile.
> 
> JEEEEZZZ! Dang me. You measure resistance (ohms) with an ohm meter and
> the impedance (amperage) with an ampprobe. Why they changed up the words
> is beyond me. 
> 
> Man-wai, the deal is when that Ohm's Law equation came out, they used
> the words Energy, Impedance and Resistance.  Now they are:
> 	Voltage, Amperage and Ohms.  
> 
> Yet, Ohms law is still written as  E = I X R ...out of respect for the
> old geeze who figured it all out for us. You're supposed to be
> enlightened to the point of doing the conversion in your head. Thanks to
> Meester Senor Bandel of Panama for pointing out my faux paux. <smiles
> grimly> At least he'll be old and grey someday too... falling face first
> into his oatmeal. I get no small measure of satisfaction from that fact.
> <smirks> Ric

True, you do measure resistance with an Ohm meter.

You *cannot* measure impedance with an Ohm meter.  You need some special
equipment.  In lab, we did it with a frequency generator and and
oscilloscope.  VERY simply, Ohms work for DC and impedance is for
everything else.  Impedance is a function of frequency. [R(f)]

In my current class, even Ohm's law is not fixed.  Thanks to a guy named
Maxwell.  The 'E' in Ohm's law stands for Electro-Motive Force, or EMF,
what we usually now call voltage.

We need to stop this thread before one of my professor's sees it and
goes back to change my grade.  That would be bad, I am done in May.

    -- Alma