# Total Impedance in this Circuit

Discussion in 'Homework Help' started by cheyenne, Mar 19, 2008.

1. ### cheyenne Thread Starter Active Member

Dec 6, 2007
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0
I was asked to find the total impedance in this circuit and I got the answer:
= 17 Angle -47.13. Is it possible for someone to check this for me to see if i've done it correctly, thanks.

Edit: I also got the voltage across the inductor as being = 8.32 V Angle 33.7.

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2. ### cheyenne Thread Starter Active Member

Dec 6, 2007
48
0
Is anyone able to help me out here?

3. ### The Electrician AAC Fanatic!

Oct 9, 2007
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494
I get a total impedance of 16.87 angle -46.8476

Are you using a calculator that can do complex arithmetic? You seem to have some slight errors in your arithmetic.

For the voltage across the inductor, I get 4.932 angle 80.5377

I calculated it by finding the equivalent impedance of the right branch and the middle branch in parallel (I got 11.5385 - j2.3077), and then calculating the voltage across those two branches by treating their parallel equivalent plus the -j10 as a voltage divider ( I got 5.6757 + j4.0541 volts). Then, knowing the voltage across the middle branch, calculate the current through that branch by dividing the voltage across the branch (5.6757 + j4.0541 volts) by the impedance of the branch (15 + j15); the current is .3243 - j.0541. Finally, knowing the current in the middle branch, multiply the current by the impedance of the inductor (0 + j15) to get the voltage across the inductor (.8108 + j4.8649) and convert to polar coordinates.

4. ### cheyenne Thread Starter Active Member

Dec 6, 2007
48
0
Hi, thanks. It was my poor rounding that caused the error in the first part and thanks for showing me how to find the voltage across the inductor.

5. ### hgmjr Retired Moderator

Jan 28, 2005
9,029
219
The answer I obtained from my calculations of the total impedance agrees with electrician's.

hgmjr

6. ### abbas_6007 New Member

Sep 7, 2009
5
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Eectrician's answer is approximately right not 100%. Try it again

7. ### The Electrician AAC Fanatic!

Oct 9, 2007
2,711
494
I tried it again, and I got the same result.

Show us what you get, and how you did it.

8. ### Perfectboy New Member

Sep 9, 2009
9
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But i also got the same result! What's my problem! 