RLC Circuit: Find Applied Source Voltage

[uzair_ha91]

Homework Statement

[PLAIN]http://img255.imageshack.us/img255/3048/56893213.jpg
Find the voltage of the applied source.

Homework Equations

I=V/R
Kirchoff's Voltage Law

The Attempt at a Solution

Applying KVL.
V= 40 + 50 +20
=110

Is this question that simple?
Or am I missing something?

 

[willem2]

The voltages across the capacitor and the inductor don't have the same phase, so you can't add them.

 

[uzair_ha91]

But the values of resistance and reactance aren't given for capacitor and inductor, so how should I calculate their voltages?
Or I just can't add them anyway? So how to reach the answer?

 

[uzair_ha91]

What if I took them as vectors?
VR = 40
VC = -20i
VL = 50i

V=40+30i
The magnitude of this is sqrt (402 + 302) = sqrt (1600 + 900) = sqrt(2500) = 50 volts
Is this correct?

 

[willem2]

You don't know what the direction of those vectors is.

Use the equation for a voltage divider

$$V_R = \frac {R} {X}$$

$$V_L = \frac {i \omega L } { X}$$

$$V_C = ...$$

where X is the total reactance of the circuit, a complex number that is a
function of $\omega$ R, C and L

now compute the magnitude of V_L/V_R and V_C/V_R

this will give a relation between R and $\omega L$ and $\omega C$

which you can substitute in the equation for V_R above.

 

[uzair_ha91]

But the values for R and $\omega L$ and $\omega C$ are not given.