# Find thevenin resistance in ladder network

Discussion in 'Homework Help' started by Beturun, Jan 27, 2014.

1. ### Beturun Thread Starter New Member

Jan 27, 2014
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Hey guys, I need help in finding the thevenin resistance of a circuit. I'm mostly having trouble telling whats in series and whats in parallel in the circuit. In the question is says to treat R7 as a load resistor and remove R7, then find the thevenin equivalant for the rest of the circuit and then reattach R7

So I'm thinking thevenin resistance it would be done like this (R1+R6+R8 + (R2||R4+R3||R5)) but i'm not sure. To find the thevenin voltage would that be the same as the normal voltage? Thanks for any and all help on this matter

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Feb 19, 2010
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lol

3. ### Beturun Thread Starter New Member

Jan 27, 2014
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I wasn't able to find a similar problem (square with resistors on all 4 sides) and it's the first week of classes, this is just stuff that we should know from a previous class and was given as a reresher I guess. We didn't go over it in class and the other questions in the assignment seem to point toward problems in the book ("#2 #50 (8th ed) design a loaded voltage divider subject to constraints.") but they give no page number and they don't really ask a clear question.

4. ### shteii01 AAC Fanatic!

Feb 19, 2010
3,500
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The difference between Engineer and technician is that Engineer takes principals and applies them to specific practical problems.

You are a technician, you are looking for exact example to solve your specific problem. You are unable to apply the principals that govern the problem.

I suggest you go back to whatever textbook you have that explains the process of finding Thevenin equivalent circuit.
Or.
You can keep looking for example that is exactly like your problem, and if you find one, copy the solution.

Apr 26, 2005
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6. ### JoeJester AAC Fanatic!

Apr 26, 2005
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Last edited: Jan 27, 2014
7. ### t_n_k AAC Fanatic!

Mar 6, 2009
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I'm puzzled by that statement. Are you saying technicians are incapable of synthesizing a solution to a previously unencountered problem? I've met several "engineers" who lack that capability.

Some of the best amateur radio operators have no formal engineering training but they are able to design and build some extraordinarily brilliant apparatus.

8. ### WBahn Moderator

Mar 31, 2012
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I know what you are trying to say, but I suspect you are going to get a lot of well-deserved flak for saying it this way.

If we used the terms "engineer" and "technician" to describe a person's level of ability independent of what their formal and informal background was, then perhaps these terms could be defined in something along the lines you describe. Perhaps a better way would be to have some kind of a continuous spectrum in which at one end (the left end, for conversation's sake) the person can only do what you describe for "technician" and at the other end the person can fully do what you describe for "engineer". A given person at a given moment in time regarding a given topic would then sit at some point along that line. We might then partition that line at several points and associate terms like "student", "technician", and "engineer", perhaps with several degree qualifies such as "junior" and "senior" on each.

In that ideal world, everyone starts out at the same point (the far left end) and then progresses toward the right over time. Some people move further and/or faster than others, but the label describes only individual ability and not job title or degree title.

But in reality, of course, the titles are what are used primarily and a given person's skill may or may not match their official title (job or degree) very well, with some people performing way, way above the stereotype and others performing way, way below it.

9. ### WBahn Moderator

Mar 31, 2012
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Two devices are in series if whatever current flows in one MUST flow in the other.

Two devices are in parallel if whatever voltage appears across one MUST appear across the other.

One way to start out, particularly when you are new, is to identify two resistors that are either in series or in parallel and then replace those two with a new resistor that is equal to the combination of the original two. Then, with that replacement made, do this same thing again. Keep doing this until you are down to a single resistor.

Although it doesn't apply to this circuit, you need to be aware that there are circuits in which no components are in series or parallel. In those cases, you have to use more capable analysis techniques.

10. ### LvW Active Member

Jun 13, 2013
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I think, this thread shows that forums like AAC can be "dangerous" in a certain sense and for certain people - because it is so easy to ask a question (in some cases even with uncomplete information on the task) rather than trying to find at least an approach for an answer.
What I mean is: Some people stop or even do not start thinking but simply hope that somebody else has an answer.
As another example - recently, there was a question in this forum like "is the current through a short large or small ?".
Of course, I do not vote for closing electronic forums. But I like to remind all of us that, finally, it is only to the OP`s advantage to guide him rather than simply answer his question.
(I know, that - in particular, in the homework section most of us follow this guideline. However, some newbies know about this and place their questions in another section).

Jun 13, 2013
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12. ### Seddie777 New Member

Jan 28, 2014
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Though I do agree, I also think others may have been a bit harsh. If this is truly an electronics forum for everyone that includes those learning even the basics. You do need to learn this for yourself, but hopefully I can point you in the right direction. Thevenin equivalents deal with "removing" and "shorting" certain portions of the circuit strategically. You solve a much simpler circuit which gives you one answer, then that answer can be used to find others. You essentially solve multiple small, easier problems instead of one large much more complex one. Now where I do agree with most others is that you must take your knowledge (based on the question and complexity of your problem I assume you have done this before) of previous circuits you have done and apply it to this. Not every problem will have a set equation. Simply google some examples also, that will likely help significantly. If you need more detail, let me know, but I certainly wont solve it for you

13. ### JoeJester AAC Fanatic!

Apr 26, 2005
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For those who try to mask homework questions in other areas, I just report that to the moderators and let them move the thread.

14. ### JoeJester AAC Fanatic!

Apr 26, 2005
3,399
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Duplicate posting from phone..... sorry

Last edited: Jan 28, 2014