# Series RLC info query

Discussion in 'Homework Help' started by stuartsjg, Jun 16, 2009.

1. ### stuartsjg Thread Starter New Member

Jun 16, 2009
3
0
Hi,
Im new to the forum so HI everybody!

and am at the section where you are putting the reactances into the table:

The guide says "apply ohms law" but i cant see how you get the resulting values for currents.

I prefer the 'j' notation as opposed to angular notation.

There must be something im not seeing that combines the real and invisible part (j part) so you can get the two numbers!?

Any guidance would be good.

Thanks,
Stuart

2. ### The Electrician AAC Fanatic!

Oct 9, 2007
2,666
473
When I use a calculator that can do complex arithmetic, I get exactly the results given in the example.

If you aren't using a calculator or program that do complex arithmetic, then you must be doing the complex arithmetic yourself.

Show the details of the computation and somebody can show you where you went wrong.

3. ### stuartsjg Thread Starter New Member

Jun 16, 2009
3
0
I'm making up an excel sheet do to things for me starting from basic input values. Have got it so far as the current.

The guide says "use ohm's law"

So, i have 250 - j1523.3 Ohms at 120v

I = E/Z
I = 120/250 = 0.48A
I = 120/1523.3 = 78.8mA

Using a non-complex arithmetic calculator, how would you do the calculation you done using the complex one?

Thanks,
Stuart

ps. im sure my calc can do it as it succeeded at doing this in uni in my electrical degree but i cant remember how!

4. ### vvkannan Active Member

Aug 9, 2008
138
11
Hi stuartsjg,
say you have x/(y+z) you cannot divide x by y and x by z and add them.Thats what you have done.Take the conjugate of the denominator that is multiply and divide the numerator and denominator by 250 + j1523.3 .
The denominator is of the form (a+b) x (a-b).Now try it from here.

5. ### The Electrician AAC Fanatic!

Oct 9, 2007
2,666
473
I'm pretty sure Excel can do complex arithmetic. Look that up in Excel's online help. Using complex arithmetic is by far the easiest way to do it.