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Total resistance in a circuit question

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1. Homework Statement
Assuming the wires have negligible resistance, find the equivalent resistance between the terminals A and B. Answer to 2 significant figures.

upload_2016-11-10_11-57-48.png


2. Homework Equations

1/R = 1/R1 + 1/R2 ... + 1/Rn

R = R1 + R2 + Rn


3. The Attempt at a Solution

I have drawn a more simplified circuit on a piece of paper and as the horizontal wire in the middle of the circuit has no resistance I have ignored the 4 resistor below it as no current will travel through them.

I have used the resistor equations above but I can't get the right answer. It is an online question and it will only tell me if the answer is right or wrong.

Any help will be appreciated.

Thanks
 

gneill

Mentor
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Show the details of your calculation attempt.
 
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I added up the resistors in series (6 + 7) = 13

Then the two in parallel (1/10 + 1/5) = 3/10 Therefore resistance in parallel = 10/3 = 3.33

= 16 ohms
 

gneill

Mentor
20,486
2,610
I added up the resistors in series (6 + 7) = 13

Then the two in parallel (1/10 + 1/5) = 3/10 Therefore resistance in parallel = 10/3 = 3.33

= 16 ohms
Ah. Well the 6 and 7 Ohm resistors are not in series. The B terminal is joined to the junction where they meet, so that junction is not unique to just the two resistors. The B terminal has to be considered a path that current can take since it's part of where you're "measuring" the circuit resistance from.

The 5 and 10 Ohm resistors are in parallel though, so that calculation is fine. Redraw the circuit with them replaced by a single resistor and continue to simplify from there.
 
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Thank you very much I've got the right answer now.

I did 1/(3.33 + 6) + 1/7 = 0.25 Therefore resistance = 4 Ohms

I sort of get where I went wrong but I'm still getting my head round it.
 

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