[SOLVED] rms Values

[flyline19]

When I am given Irms = 10cos(500t - 45(deg)), and I need to plug it into an equation using Irms do I plug in 10<-45? or just the 10? I understand that 10 is I/sqrt(2). I guess my question is more, is the rms value just the magnitude? or is it the magnitude and angle?

 

[wwfeldman]

it will depend on what you are calculating.

if you're looking at phasors (and the like), you'll need the amplitude and the angle.
if you're looking at things like average power, you don't need the angle.

can you be more specific about the equation(s) that brought up the question?

 

[flyline19]

Here is the thing that sparked this question:

I found my Irms (Phasor) with real and imaginary components, then converted from cartesian to polar. I now have a rms magnitude and angle. When I plug into the AVG PWR eq. (Pavg = I²rms *R), do I only use the magnitude of Irms , as its the real portion of the complex pwr eq?

 

[KlausST]

Hi,

The RMS value of a sine shaped (V or I) is always: amplitude / sqrt(2).
In your case about 7.07 ... (what is your unit).

Klaus

Btw: You say " I_RMS = 10 cos ..." this is wrong. I should be: "I(t) = 10 cos ...."

 

[flyline19]

Hi,

The RMS value of a sine shaped (V or I) is always: amplitude / sqrt(2).
In your case about 7.07 ... (what is your unit).

Klaus

Btw: You say " I_RMS = 10 cos ..." this is wrong. I should be: "I(t) = 10 cos ...."

Ahh I think that I see where I was confused. an rms value is always mag/sqrt[2]. the angle is not part of the rms value itself, but is part of the V or I. Is that correct?

 

[KlausST]

Hi,

Yes. Angle does not matter, nor frequency. It does not differ between cos and sin, because both have same shape.

Klaus