# Effective Resistance [closed]

For the combination of the resistors, shown in the figure. Calculate the equivalent resistance between A and B, please help me to find the answer of this complicated question this is a question from an easy part but, I don't know how to solve this.

## closed as off-topic by Emilio Pisanty, Qmechanic♦Sep 5 '13 at 16:27

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• Start from the B end, and try to replace two resistors by an equivalent one. Then repeat until finished. It should not be hard: "resistance is futile". – babou Sep 5 '13 at 16:03
• It is not always that easy. Sometimes you have to write equations, because you cannot isolate pairs of resistors. – babou Sep 5 '13 at 16:18

# This is a homework(-like) question so I may not give a full answer.

Let $\alpha$ be the bottom resistor with 100 omega resistance.
Let $\beta$ be the middle resistor with 100 omega resistance.
Let $\gamma$ be the top resistor with 100 omega resistance.
Let $\delta$ be the resistor with 25 omega resistance.
Let $\varepsilon$ be the resistor with 120 omega resistance.
Let $\zeta$ be the resistor with 40 omega resistance.

If you see the resistors $\alpha$ and $\delta$, they are in parallel, so they add up to a resistance given by $\frac1R=\frac1{R_1}+\frac1{R_2}$. Let's call this "parallel addition".

This added up resistance is in series, with resistor $\beta$, so they're total resistance is merely their sum. Let's call this "serial addition".

This resistance is to be parallelly added to the resistor $\varepsilon$, which can be serially added to the resistor $\gamma$ and so on.

The formulas I mentioned can be obtained from any standard introductory physics or such textbook. My personal favourite is Jewett and Serway Physics for Scientists and Engineers with Modern Physics.

• If answering hardware problems isn't allowed; why did YOU answer it. You give an answer that is specific to this network; not all networks. And it is obvious, from the specific numbers in the question, that the author's full intent was for it to be solved, by inspection exactly as I explained to the "OP", as you call him/er. If it was my question on an exam paper, I would dock the student points for using the laborious method you describe; in fact I have done precisely that, for a similar network problem that had an obvious answer by inspection, that I asked on an exam paper. – user26165 Sep 8 '13 at 5:11
• Well Dimension 10, you really are touchy with your "ranting" citations. And absolutely nowhere or at any time, did I mention anybody asking or answering questions in another language (besides English) . What I DID say, was that many posters do not write in the English language. English has a robust grammar, and well defined words. Misuse of those conveys misinformation. If somebody writes " hw " instead of homework, and also writes " OP " instead of original poster, they are not writing in English. And I've got children older than you, so don't get uppity with me. – user26165 Sep 11 '13 at 6:42