RMS Power?


I often see power specifications like "100W RMS".  There is no such thing as RMS power.  Of course, you can calculate RMS value from any curve, including power curve, but it won't represent anything.  "Real" power representing heat dissipated in resistive load is "Average Power"   Pavg=Vrms*Irms.   In case of sinewaves Pavg=0.707Vpeak * 0.707Ipeak = 0.5Ppeak,  or Ppeak = 2Pavg. 

Term "RMS Power" or "watts RMS" is a mistake, very common in audio.
128x128kijanki
From Wikipedia "Audio Power"

As described above, the term average power refers to the average value of the instantaneous power waveform over time. As this is typically derived from the root mean square (RMS) of the sine wave voltage,[6] it is often referred to as "RMS power" or "watts RMS", but this is incorrect: it is not the RMS value of the power waveform (which would be a larger, but meaningless, number).[7][8][9][10] (The erroneous term "watts RMS" is actually used in CE regulations.[11]) This is also referred to as the nominal value, there being a regulatory requirement to use it.

Al, leave it (he is not going to get it).
Hi Roger,

All of us, certainly including Kijanki who is very knowledgeable technically, completely understand and are in complete agreement about the technical aspects of what is being discussed, i.e., the "basic electronics" and the math you referred to.

What he is going on about is simply the terminology that is being used.

And his point is that strictly speaking what the words "RMS power" literally mean is the RMS value of a waveform that defines how power varies as a function of time. Which would be 141.4 watts in your example, while of course 100 watts (the product of RMS voltage and RMS current) is what is actually being referred to when that phrase is used.

Regards,
-- Al
@kijanki  Al, leave it (he is not going to get it).

Thats really rude, however

Would you please be so kind as to supply a link to what you want me to read, there are several articles on Wicki. 

OH, dont worry, I will get it or apologize for not getting it. 
@almarg  And his point is that strictly speaking what the words "RMS power" literally mean is the RMS value of a waveform that defines how power varies as a function of time. Which would be 141.4 watts in your example, while of course 100 watts (the product of RMS voltage and RMS current) is what is actually being referred to when that phrase is used.


First when someone starts an OP with "there is no such thing as RMS power" whats that mean?

RMS Power doesn't vary as a function of time, instaneous power does. 

Im still waiting for the link to Wickipedia. Do you have it. Im just on pins and needles here.
Hi Roger,

I found the Wikipedia page from which Kijanki quoted (the link opens near the paragraph he quoted):

https://en.wikipedia.org/wiki/Audio_power#Continuous_power_and_%22RMS_power%22

RMS Power doesn’t vary as a function of time, instaneous power does.

To be sure it’s clear, I absolutely did not say that "RMS power" varies as a function of time, although I can see how my statement might have been misread. I said that...

... what the words "RMS power" literally mean is the RMS value of a waveform that defines how power varies as a function of time.

(The "waveform defines how power varies as a function of time"; the RMS value of that waveform of course does not define how power varies as a function of time).

Again, what Kijanki has been addressing is terminology, nothing more.

Regards,
-- Al