Making sense of watts, amps and volts -- a typo?

[Fred Abse]

The only thing I can figure is that power never becomes negative

Careful!

Power sourced vs. power dissipated.

In electromagnetic terms, the Poynting vector has direction, by
definition, too.

 

[Chiron]

It isn't pedantry, it's basic electrical principles. Something that is

The comment concerning pedantry was in reference to the flame war that
was triggered by this simple question. That was a good deal of pedantry,
as well as pointless insults and other such waste.

 

[Chiron]

Remember the Mnemonic SohCahToa?

Sine = opposite/hypoptenuse
Cosine = adjacent/hypotenuse
Tangent = opposite/adjacent

I always had it as sin, cos, tan:

Old Houses
Always Have
Old Attics

Opposite/hypotenuse;
Adjacent/hypotenuse;
Opposite/adjacent.

 

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What could we call this ratio? Seems to me that the better meters go
to great lengths to get an RMS equivalent of the readings. If RMS
equivalent readings are assumed, would not the cosine aspect apply again?

Because RMS applies to all waveforms, not just sine waves.

'True Power / Apparent power' or 'Watts / Volt-amperes' **IS** the
Cosine of the angle between VA and Watts. That would seem to disagree
with your first sentence. Would you like to reconsider the 'in all
cases' portion of the statement?

*ONLY* with sine waves. COS(theta) means nothing for a square wave, for
instance.

Also, how would the current know it was in an AC circuit? It may well
be merely on the up/down slope of a changing DC situation. Reactance
can happen with pulsating DC, too. It the same, just different....

What's sine(theta) of this random waveform?

Remember the Mnemonic SohCahToa?

Sine = opposite/hypoptenuse
Cosine = adjacent/hypotenuse
Tangent = opposite/adjacent

Since grade school, the unit circle has worked for me.

 

[Fred Abse]

What could we call this ratio? Seems to me that the better meters go
to great lengths to get an RMS equivalent of the readings. If RMS
equivalent readings are assumed, would not the cosine aspect apply again?

No. What you call the "cosine aspect" only applies when voltage and
current are *both* pure sine or cosine functions.

'True Power / Apparent power' or 'Watts / Volt-amperes' **IS** the
Cosine of the angle between VA and Watts.

I think you mean between applied voltage and resulting current. Then only
in the case of sinusoidal voltage *and* current. Consider the current
drawn from a sinusoidal supply by a full wave rectifier with reservoir
capacitor as an example. Current is far from sinusoidal, but power factor
still applies. Modern PSU designs go to some length to address this.

That would seem to disagree
with your first sentence. Would you like to reconsider the 'in all
cases' portion of the statement?
No.


Also, how would the current know it was in an AC circuit? It may well be
merely on the up/down slope of a changing DC situation. Reactance can
happen with pulsating DC, too. It the same, just different....

Reactance is a concept devised to obviate the need to do lots of tiresome
differential equations.

Power factor does not exclusively depend on reactance. Non-linear elements
have just as big an effect.

Remember the Mnemonic SohCahToa?

No. That sounds like a Native American word to me

I don't do mnemonics.