# Solve this physics problem

Thanks to all who join this discussion and make it a success....Anyone willing to solve the problem is welcomed. Enjoy it ...!!

Note by Raja Metronetizen
5 years, 4 months ago

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The correct answer is $$\frac{299R}{330} \approx .906R$$.

Using Pranav A.'s method of folding the circuit, and then applying a Delta-Y transformation (http://en.wikipedia.org/wiki/Y-%CE%94transform), I was able to reduce the circuit to a 13-resistor,10-node circuit(http://i.imgur.com/OQ0t9f8.png). From there, you can use the Node-Voltage method (http://en.wikipedia.org/wiki/Nodalanalysis), along with assuming a test voltage applied across A and B, to solve the circuit, although it requires using a rather large system of equations. If anyone knows of a way to further reduce the circuit from the 13-resistor state so that you don't have to get such a large system please tell me.

- 5 years, 4 months ago

I too had the same problem. I had to apply the Y-delta transform again and again but it wasn't ending up with nice values so I gave up.

- 5 years, 4 months ago

IF ANYONE OF YOU FIND THIS PROBLEM IN A BOOK,DON'T THINK I HAVE COPIED IT....I CREATED IT MYSELF....

- 5 years, 4 months ago

- 5 years, 4 months ago

no, sorry i don't know it..but if anyone describes me how to approach, i could understand....

- 5 years, 4 months ago

Thanks Ricky E. !! ... You've been brilliant.

- 5 years, 4 months ago

Is that a pun on the word brilliant? lol! :P

- 5 years, 4 months ago

I am not sure about it but first step is obviously folding the circuit about AB. This step retains only the half portion of circuit with all the resistors equal to R/2 except the middle line of four resistors which still have R resistance. The second step involves removing "fake" nodes but I still need to figure out those nodes.

- 5 years, 4 months ago

there is a great theory to compute the equivalent resistance of such big complicated circuits of resistance....it opines that if any system of resistance is symmetrical about its two opposite point here the two points "A" and "B" then all the points equidistant from this two terminal would be at same potential ......i knew this fact or theorem but i don't know how to apply it here.......i think it would have to be applied here.....try it....

- 5 years, 4 months ago

Delta Y transformation is the only way(known to me), and you will definitely need a good calculator!!

- 5 years, 4 months ago

well really...... current had to do lot of hard work!!!!! please clearly mention your problem, the question is not clearly visible.

- 5 years, 4 months ago

Turns out to be 'R' (I think so)

- 5 years, 4 months ago

Image Link I simulated this problem. these resistors have 21/19R ohms. I think It is hard to solve by hand.

- 5 years, 4 months ago

Very complicated......

- 5 years, 4 months ago

What are the values of the resistors...are they all same or different

- 5 years, 4 months ago

you have not seen the whole problem..... i have written it in the right corner........ however, each and every resistor have equivalent resistance=R.......

- 5 years, 4 months ago

I think the answer is 52R/45.

- 5 years, 4 months ago

Consider each resistor 'R' Fold the circuit along AB. When resistors overlap, consider it a parallel combination and replace it by 'R/2'.

So, except the 4 resistors in the AB line, you get half the circuit where each resistor is 'R/2'. Now, draw a line of symmetry along the perpendicular bisector of AB. There are two nodes on this line, the mid point of AB and the midpoint of the bottom line. Remove these connections as follows : for the top:

something like --------- ^

and for the bottom, something like : v

Now use the normal laws and solve the problem.

- 5 years, 4 months ago

- 5 years, 1 month ago

first we change the delta connection into star connection and now we solve it easy series and parallal combination

- 5 years, 4 months ago

would you please elaborate it....?...i'm unaware of these connections.....

- 5 years, 4 months ago

http://en.wikipedia.org/wiki/Y-%CE%94_transform

- 5 years, 4 months ago