Wire you confused?

Find the equivalent resistance in the following circuit.


The answer is 12.5.

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3 solutions

Khaled Barie
Nov 15, 2014

This may be somewhat complex but let's approach it in a simpler way. I'm going to place points on the circuit to define certain positions:

Figure 1

since the green wire is nothing but a connection between points C and D, we can change the location of the Terminal of the 3 ohm on point D to any place on the green wire:

Figure 2

now it is obvious:

6 parallel to 3 = 2ohms

7 in series with 2 = 9 ohms

9 in parallel with 9 = 4.5 ohms

4.5 in series with 8 = 12.5 ohms

I feel stupid for using advanced methods as delta-star transformations instead of looking using simple topology modifications on the circuit. But it still works, hahaha.

Mikael Marcondes - 6 years, 4 months ago
Ahmed Kamal
Jan 22, 2015

It could be more confused if you had replaced the 7ohm resistor with a wire :) .

Mohamed Hussein
Nov 15, 2014

The 6 ohm resistor is cancelled...7&3 resistors are series R=10 ohm..10&9 are parallel R=4.7 THEN 8&4.7 resistors are series R total is 12.7 ohm

Why did you assume that 6Ω is cancelled ? I see no reason why it should.

Khaled Barie - 6 years, 7 months ago

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Because of the wire. The current will moves in 9ohm will find the way of 6ohm and the wire so it will move in the wire

Manal Mansi - 6 years ago

wouldn't the current in 9 ohm branch move in the branch free of resistors?

Noha Hany - 6 years, 6 months ago

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yes, but you have 6Ω resistor and 3Ω resistor are parallel, and all of them series with 7Ω resistor by calculation this branch equals to 9Ω. the first branch and the second branch equal to 9Ω and they are parallel by calculation the sum of the two branches equal to 4.5Ω and the two branches are series with 8Ω resistor by calculation the equivalent resistance equal to 12.5Ω

Abdulrahman El Shafei - 6 years, 5 months ago

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