Mayobe

Oh my gosh I found it. Thank you very much for your advice. It turns out my problem was with unit conversions.

The steps I took to get the correct answer were:

XL = 2pi*fL*10^-3 (for unit correction from mH to H)

XC = 1 / (2pi*fC*10^-6) (unit correction from micro F)

X = |XL - XC|

theta = atan(X/R)

Z = sqrt(R^2 + X^2)

I = V*10^-3/Z (correction from mV to V)

P = ((V*10^-3) * I * cos(theta)) watts

When I corrected that to mW it was correct. FINALLY!

Thank you for your help! I just needed one more nudge to get it to click for me.

Hello.

I'm taking a pre-calc course and I came across a bizzare question that I have no idea about. I really have very little interest in electrical engineering (sorry), but I'm trying to figure out how to turn this question into mathematics so I can solve it.

First we're given the equation P = VI cos θ. P is in watts, V is effective voltage, I is effective current and theta is the phase angle between current and voltage. We're given V, then told that the circuit has a resistor with set ohms, an inductor with set mH and a capacitor with set μF. The frequency is also provided in Hz. We're asked to determine the value of P in mW.

I've been browsing the web for quite a while now and I can't make head nor tail of the things I've seen. I just want to turn this into math so I can do something with it apart from writing 'I am not an electrical engineer.' as the answer.

I'm fine with calc and vectors don't scare me, I just don't understand what all these different terms mean (like phi vs theta for angles and X or Z or etc.) and I don't grasp the process used to get the V, I and theta that I need.

Any advice would be greatly appreciated.