# Power of a sine wave

Hello,

What is the formula to calculate the power (W) of a sine wave electrical signal traveling through a wire if I know the frequency, voltage, and current?

Thanks,
Jason O

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NoTime
Homework Helper
You need to know the phase angle.
Unless you just want to know how much power the wire is consuming.
In which case you need R_wire.

berkeman
Mentor
If the voltage and current are in phase (your load is resistive only), then the power is just P = V * I, independent of frequency.

berkeman said:
If the voltage and current are in phase (your load is resistive only), then the power is just P = V * I, independent of frequency.
So you are saying that a wire carrying 100 volts at 60Hz has the same amount of power as a wire carrying 100 volts at 120Hz or 1kHz (assuming the same load in all three cases)? I heard somewhere that if you double the frequency of the wave, that the power is 4 times as much, is that true?

Thanks,
Jason O

NoTime
Homework Helper
No, it's not.
Wave shape will make a difference in power.
Frequency only becomes important (if the load is resistive) as it gets high enough for the skin effect to make a significant contributation.

Since you seem primarily interested in coils then note that P=V * I does not apply to what you are doing.

es1

NoTime
Homework Helper
Nice pages es1.
Since the OP seems to be contemplating square waves the page 2 doesn't really apply to him.

A square wave reflects the sum of a large number of
different frequency sine waves.
This can be tricky in inductive circuits.

Perhaps Jdo should coinsider geting a function genenerator that can produce sine waves.