R. Measures wrote:
>
> On Mar 25, 2005, at 2:00 PM, David Kirkby wrote:
>
>> R.Measures wrote:
>>
>>>
>>>>
>>>> You can not find RMS power by multiplying RMS voltage by RMS current.
>>>>
>>>
>>> I disagree. .
>>>
>>
>> Rich, I think you are wrong. Here's my reasoning - I may well be
>> wrong, as maths never was a good point of mine.
>>
>> You need to understand calculus to properly work out the RMS of an
>> arbitrary waveform, as you probably know.
>> Hence this explanation will really only be of use to someone who
>> knows integration. But I can't see a simple way of computing the RMS
>> value of the power, without it. People will just argue, but if you go
>> back to first principles, you should get the right answer.
>
>
> The right answer is that RMS current x RMS potential = AC P
Any chance of you substantiating what you have said?
You stated you disagreed with Gary (K4FMX) who said
> You can not find RMS power by multiplying RMS voltage by RMS current."
Now I think you are wrong to disagree with K4FMX. I don;'t believe a
simple multiple of the RMS values of voltage and current gives the rms
power.
If you have 1V peak across 1 Ohm you have an RMS voltage of 0.707 V, and
RMS current of 0.707A. If you multiply the RMS voltage by the RMS
current you get 0.5W. (0.707*0.707=0.5). But I computed, and have fully
justified, that the actual RMS power is 0.612273 Watts for a 1V peak. I
don't think the term RMS power is very useful, but if you want to use
the term, then at least use it correctly.
I stuck a few notes at
http://www.g8wrb.org/useful-stuff/index.html
where you will find an html page on it
http://www.g8wrb.org/useful-stuff/rmspower.html
but its best to look at http://www.g8wrb.org/useful-stuff/index.html
, as you can find other file formats, that are more useful.
You have rather a habbit Rich of saying things without justification.
Tell me where my analysis is wrong? Where is my mistake? I'm not saying
there is no error (I admitted maths is not a strong point of mine) - but
at least I don't dismiss other peoples comments and just think mine is
right all the time. I try to substantiate what I say, rather than come
back with one-liners that you expect everyone to take as gospel.
--
Dr. David Kirkby,
G8WRB
Please check out http://www.g8wrb.org/
of if you live in Essex http://www.southminster-branch-line.org.uk/
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