# Reactive+resistive

Discussion in 'Homework Help' started by ctishman, Mar 17, 2013.

1. ### ctishman Thread Starter New Member

Oct 12, 2011
9
0
So I've got this question for a take-home final. I've changed the numbers, because I need to know how it works for the in-class, rather than just getting an answer:

I was given the following circuit:

which I then simplified to this:

I'm trying to

1. figure out voltage drops so I can use that to
2. get component values and then
3. Figure out what type of inductor I'd need to use to balance this.

My question is this: I can see that each branch gets the 100V evenly, but I don't know how to work out voltage division between resistive and reactive components to figure out component values. Can I use the voltage divider rule, or do I have to perform some voodoo?

2. ### MrChips Moderator

Oct 2, 2009
12,449
3,363
Inductors and capacitors have reactance which is a function of frequency. You cannot simply combine resistors with inductors and capacitors as you would resistances.

Inductive and capacitive reactances are 90 degrees out of phase with the resistance.
Use a phasor diagram in order to combine reactance with resistance.

3. ### ctishman Thread Starter New Member

Oct 12, 2011
9
0
Aye, I know that much, but i'm trying to figure out at least one component value. That requires figuring out how much voltage is applied where, and I don't know if I can do that with the information I've been given.

4. ### WBahn Moderator

Mar 31, 2012
17,763
4,800
Why put your components in series? You can put anything in the boxes you want as long as the net effect is what is written on the box.

If they are in series, then you have to deal with the fact that the voltages across each are not in phase.

But if they are in parallel......

ctishman likes this.
5. ### ctishman Thread Starter New Member

Oct 12, 2011
9
0
Ooooooh… So parallel-within-parallel. I hadn't considered that. It would save me work, though it would make any work with current a nightmare. Worth a shot! Thanks!