# Working out parallel complex impedances

Discussion in 'Homework Help' started by vane, Mar 20, 2010.

1. ### vane Thread Starter Active Member

Feb 28, 2007
181
0
I have a question on my maths assignment at college which involves working out he total of two parallel complex impedances.

I am given:

Z1 = 6 + 5j &
Z2 = -2 - 4j

I have written notes about multiplying, dividing, adding and taking away these complex numbers i am just a bit puzzled as to which one I use to work out the combined impedance.

Any help would be greatly appreciated as soon as possible so that I can get the assignment done and move onto the next fun installment!!!......

2. ### jlcstrat Active Member

Jun 19, 2009
58
3
It can be done the same way as simple resistances...product over sum, etc.

3. ### vane Thread Starter Active Member

Feb 28, 2007
181
0
I think it is a specific way I am supposed to do it

Could it be:
(Z1 x Z2)/(Z1+Z2)?

This is the reciprocal method is it not? I think I may have figured it out myself

4. ### jlcstrat Active Member

Jun 19, 2009
58
3
Yeah, that's product over sum. The reciprocal would be:
Inverse(1/z1 +1/z2)

5. ### vane Thread Starter Active Member

Feb 28, 2007
181
0
thank you very much for your ultra fast help!

Jun 19, 2009
58
3
No problem.

7. ### hgmjr Moderator

Jan 28, 2005
9,030
214
You are aware that you must flip back and forth between polar and rectangular coordinates depending on the operation you are performing, right?

Multiplication and division are done in polar coordinates and addition and substraction are performed in rectangular coordinates.

hgmjr

8. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
Are you sure that is necessary. I've never had a problem with multiplying complex impedances and removing the j from the denominator by multiplying top and bottom by the complex conjugate of the denominator.

I know that it can be convenient to use polar notation, but it is not absolutely necessary. Is it?

9. ### Ghar Active Member

Mar 8, 2010
655
73
Polar and rectangular notations are entirely equivalent, it's just easier to work with one over the other sometimes.
You can stick with one if you really want to.

Though, adding in polar is the most counter productive thing ever...

Last edited: Mar 20, 2010
10. ### The Electrician AAC Fanatic!

Oct 9, 2007
2,301
338
If you're going to be doing this sort of thing much, such as you will if you're studying Electrical Engineering, it would be worthwhile to get a calculator that can do complex arithmetic.

As an alternative, I think you can find applets on the web for doing it.

11. ### hgmjr Moderator

Jan 28, 2005
9,030
214
I am certain that your technique is a viable one. It is just that I have always tackled these problems by converting to the coordinate system suited to the math operation that I needed to perform.

hgmjr

Last edited: Mar 20, 2010
12. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
Whew -- that's a relief. I was ready to believe you had discovered some new mathematics!