What is the rms potential difference across the resistor?

[mr_coffee]

Hello every9one I'm stuck on finding the first part:
A series RLC circuit is driven by an alternating source at a frequency of 380 Hz and an emf amplitude of 90.0 V. The resistance is 20.0 , the capacitance is 12.1 µF, and the inductance is 24.2 mH.

What is the rms potential difference across the resistor?
my first answer was wrong,
Am i t hinking this right?
Vab = Vmax sin(wt)
Vab = iR
i = 90/20 = 4.5, but thisn't isn't i max is it?
do i have to take i/sqrt(2) to get i max?
then with i max can i find the rms across the ressitor?
I found a formula that syas:
Vab = Vmax*sin(wt) but time isn't given at all, netiehr isVmax!

 

[Integral]

You must set up an equation for the current involving ALL of the circuit components. You cannot get the answer by considering the resistance alone.

 

[Astronuc]

This is not correct {i = 90/20 = 4.5 A}.

As Integral indicated, the 90 volts applies to the R + L + C in series.

R is a non-reactive component so the voltage drop will be in phase with the applied volatage. L and C are reactive components so the voltage drops will be out of phase with the applied voltage.

So V_R has same shape, but different amplitude, than V.