# Impedance solution

Discussion in 'Homework Help' started by cisseywolf1, Feb 22, 2007.

1. ### cisseywolf1 Thread Starter New Member

Feb 22, 2007
2
0
Well this is my first time on a sight like this, so all please have patience. Here is my question.

Find the impedence in a series RL circuit with R=50 ohms and L=470 microHenries at a frequency of 10kHz. If some one figures this out would you please put it in terms I can understand.

I just started this class and I am having a very hard time. Fresh out of high school 32 yrs ago. I am now in college for the first time.

2. ### Dave Retired Moderator

Nov 17, 2003
6,960
145
Hi,

You should have a look in the tutorial at Volume II - Chapter 3.3 here at All About Circuits. Work through the tutorial and if you have any questions feel free to post them up.

As a side point, be sure to check out the whole on-line e-book to help you with the rest of your studies.

Dave

3. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
In a series RL circuit you can add the impedances of the components. The impedance of a resistor is just its resistance and it is not frequency dependent. Ahhh but the impedance of an inductor depends on the frequency. It is
Code ( (Unknown Language)):
1.
2. j*w*L
3. where j is the imaginary unit aka sqrt(-1)
4. w is 2*pi*frequency
5. L is the inductance in henries
6.
The result will be a complex number = R + j*2*pi*f*L
From this complex number you can calculate the magnitude using the pythagorean theorem and you can compute the angle as the
arctan((2*pi*f*L)/R)

c'est facile! n'est pas?

4. ### nomurphy AAC Fanatic!

Aug 8, 2005
567
12
It can also be as simple as:

inductive reactance = XL = 2*pi*F*L

impedance = Z = sqrt(XL^2 + R^2)

5. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
As I said you can compute the magnitude of the complex impedance with the pythagorean theorem.