I'm having real trouble understanding some concepts in RLC circuits. If I have a circuit like this. The effective voltage is 120 V. What is the required frequency for resistor to release power of 250 W? I want to really understand this on a deeper level so please make the explanation detailed. I know that the power is P = VI but what voltage should (maximum or effective) I use, what current? How to calculate current if I have voltage? Why can't I just use P = V^2/R or P = V^2/Z? I'm really bothered by this and AC circuits seem very complicated. And what about the voltage drop in series circuit, does that affect the result? And also, when is P = VIcos(phi) used??? Can i use it here? And what if I wanted to calculate the energy released by the inductor or capacitor?