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Total resistance in a circuit question

  1. Nov 10, 2016 #1
    1. The problem statement, all variables and given/known data
    Assuming the wires have negligible resistance, find the equivalent resistance between the terminals A and B. Answer to 2 significant figures.


    2. Relevant 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.

  2. jcsd
  3. Nov 10, 2016 #2


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    Staff: Mentor

    Show the details of your calculation attempt.
  4. Nov 10, 2016 #3
    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
  5. Nov 10, 2016 #4


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    Staff: Mentor

    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.
  6. Nov 10, 2016 #5
    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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