# Reactance

Discussion in 'Homework Help' started by Robert.Adams, Mar 31, 2010.

Feb 16, 2010
112
5
I have an exemption test for Circuits in 2 days and I've been doing practice problems.

I came across this and am very confused how the reactance switches signs in the simplify step.

Can someone explain this to me or is it a typo on that site (Like I hope it is.)?

Thanks.

2. ### hondabones Active Member

Sep 29, 2009
123
1
Did you mean the impedance?

2k - 250 = +1750

Feb 16, 2010
112
5
No, I mean just the reactance part of the impedance in the step that converts to milli instead of kilo. It becomes 1/3m + 1m - j0.57m

The signs on the DC resistance stayed positive and the reactance due to the inductor/cap flipped (It does come out as the right magnitude).

EDIT: Oh Snap! I got it...I think. It is (1 < 0)/(1750 < 90) which makes it become -90.

4. ### t_n_k AAC Fanatic!

Mar 6, 2009
5,448
783
I'm guessing your question is how does one get .....

$\frac{1}{j1750}=-j0.571m$

Are we agreed that 'm' just stands for $10^{-3}$

So

$\frac{1}{1750}=0.571 X 10^{-3}=0.571m$

Also remember that for the complex operator 'j'

$\frac{1}{j}=-j$

combining these two concepts

$\frac{1}{j1750}=-j0.571m$

Or you do it like you did in your EDIT .....

Last edited: Apr 1, 2010