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
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Is anyone able to help me out here?

3. The Electrician AAC Fanatic!

Oct 9, 2007
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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 Moderator

Jan 28, 2005
9,030
214
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
2,300
335
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
0
But i also got the same result! What's my problem!