a quiz about AC power

[refference]

Hi 4fun ,

You are absolutely correct !!!! The measure confirm
all of eletricity theory .

The 45’s settings , too !!!

But , you make me unhappy , because the nice “side”
of this thread was the controversy , that has just ended
with your brilliant demonstration of the answer , by both
ways : theoretic and practical ( lab measures ) . No pro-
blem , we need to create another simple question , with
the same level of controversy . It’s good to teach and
to learn .

No doubt , the correct answer is half power ( 25 Watts ) .

The polemic and controversy that have been generated
by this thread , started by Vax 9000 , with a very , very
simple question , has been VERY , VERY good for all of
us because the knowledge about RMS value of differents
wave’s shape is a fundamental point to all people that likes
or needs to build and design power supplies or power amps .

Congratulations ,

Carlos

[AKN]

Hi Carlos!

Nice of you to show up!

I am glad that we could agree finally!

[dnsey]

Does the utility wattmeter register the DC component of the power used?

No!
That's the main reason that they insist on PFC caps where appropriate, otherwise a proportion of the energy use would not be registered.

[AndrewT]

Hi,
The Power Factor Correction (PFC) capacitor is to reduce the phase angle of the load.

Large motors and transformers can use electricity at large phase angles but the heating effect in the supply cables, transformers and generators is related to the peak currents.
High phase angle increases the heating effect for NO USEFULL increase in power delivered.

PFC is not there to block or reduce the DC component whether from even harmonic distortion or from peak waveform shaving.

[dnsey]

I agree that this is the 'engineering' argument, but the commercial reason is mainly to do with metering.
Why would supply companies worry very much that the power supplied was doing no useful work, as long as they could charge for it? Most suppliers insist on a PF of over 0.85 to ensure that energy is correctly metered.
Take the extreme example: If our diode-equipped soldering iron was one of 1000 in a large factory, all connected in the same way, the facility would be consuming a considerable current which could not be registered by the eddy-current motor driving a standard consumer meter, which responds only to the in-phase AC component).
To put it another way: as you say, high I/V phase angle decreases the work done by, in this case, the meter, but the unregistered power is still available for space-heating or whatever, free of charge.

[AudioFreak]

Not sure if it's been mentioned already but in areas where the grid is not really upto the task power companies demand a given power factor so that less power is wasted in distribution which in turn puts less strain on the generators.