# Total resistance + Thevanin problems

Discussion in 'General Electronics Chat' started by Dritech, Nov 11, 2012.

1. ### Dritech Thread Starter Well-Known Member

Sep 21, 2011
808
6
Hi all,

I have some problems regarding total resistance and Thevenin.

Problem 1:

In the first attachment, is the 2ohms in parallel with the 6ohms, total in parallel
with the 8ohms and the total in series with the 10ohms ??

Problem 2:

In the other attachments I am trying to find I load using Thevenin theorem, but the current is not matching with the correct answer. Does anyone know what am i doing wrong?

Thanks in advance and sorry for my poor English.

File size:
13.6 KB
Views:
26
File size:
292.5 KB
Views:
34
File size:
297.4 KB
Views:
29
2. ### Jony130 AAC Fanatic!

Feb 17, 2009
4,431
1,257
Problem 1:

2Ω resistor is short by the wire.

Problem 2

I got the same answer as you

Last edited: Nov 11, 2012
3. ### Dritech Thread Starter Well-Known Member

Sep 21, 2011
808
6

Does that mean that i have to ignore the 2 ohms (i.e. 6 in parallel with 8, result in series with 10 ??

4. ### Jony130 AAC Fanatic!

Feb 17, 2009
4,431
1,257
Yes, exactly you shoudl ignore 2Ω resistor.
And as you said Rtot is equal Rtot = 10Ω + 6Ω||8Ω

Dritech likes this.
5. ### Dritech Thread Starter Well-Known Member

Sep 21, 2011
808
6
Hi again,

I have the attached circuit with parallel and series resistors. Are they as follow:

12//18 --- result//10 ---- result2//22 ---- result3 + 15 ??

File size:
292.9 KB
Views:
22
6. ### Dritech Thread Starter Well-Known Member

Sep 21, 2011
808
6
And in this circuit are the 22 + 15 .... result//18 .... result2 + 12 + 10 ???

File size:
277.6 KB
Views:
19
7. ### Jony130 AAC Fanatic!

Feb 17, 2009
4,431
1,257
Resistance seen from this current source terminal is equal to
Rtot = ((22+15)||18) + 12 + 10 = 34.109R

And resistance seen from 48V voltage source terminal is equal to

Rtot = 22 + 18 + 15

8. ### Dritech Thread Starter Well-Known Member

Sep 21, 2011
808
6

And what happen with the 12 and 10 resistors please?

9. ### Jony130 AAC Fanatic!

Feb 17, 2009
4,431
1,257
The 48V source current can flow only in closed loop. So how can he flow via 12 and 10 where we have a open circuit?

Dritech likes this.

Sep 21, 2011
808
6

11. ### Dritech Thread Starter Well-Known Member

Sep 21, 2011
808
6
Hi again,
can someone tell me how to work the total resistance of the attached circuit please ?

File size:
10.6 KB
Views:
17
12. ### Dritech Thread Starter Well-Known Member

Sep 21, 2011
808
6
If I work it as below, is it correct?

((R1//R2)//R3) + (R4//R5)

13. ### Jony130 AAC Fanatic!

Feb 17, 2009
4,431
1,257
Well, between which terminals you want to find this total resistance?
Also you can always use delta-wye transformation.

14. ### Dritech Thread Starter Well-Known Member

Sep 21, 2011
808
6
Hi Jony130,

I want to find the total resistance from the terminals of the load resistor which is marked in red in the picture attached below. I removed the load resistor since i meed to find the current on each resistor using Thevenin theorem (so I think I cannot use delta to star transformation)

File size:
29.7 KB
Views:
18
15. ### Jony130 AAC Fanatic!

Feb 17, 2009
4,431
1,257
If so I think that Rtot = R3||(R1||R4 + R2||R5)

Dritech likes this.