On Dec 27, 10:53*am, Cecil Moore wrote:
Keith Dysart wrote:
It is worth doing to convince yourself. Then examine
P(t) to understand how the instaneous energy transfer
varies with time.

Oh, I know how to integrate P(t).

But did you know that your favourite V * I * cos(theta)
was derived from the function describing instantaneous
power?

But I don't
comprehend the utility of the following:

The instantaneous value of voltage is 10 volts.
The instantaneous value of current is 1 amp.
The voltage and current are in phase.

The instantaneous power is 10 joules per 0 sec?

There is definitely a problem with that.

But an instantaneous value of 10 joules/sec; that
is useful. With the function describing the
intantaneous values with respect to time, you
can integrate. You can find the total energy
transfered. You can find when it is transferred.
Is it steady? Or does it vary? There is lots
to learn.

You can even learn that when the instantaneous
power at some point is 0 for all instances,
then no energy is transferred. That would be
a useful learning.

...Keith