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Homework Help: Calculating the Effect of an Electrical Short or Open on a Series Circuit

  1. Oct 28, 2009 #1
    1. The problem statement, all variables and given/known data
    I have several problems in which I am to solve for all variables in a series circuit. Then I am given a follow-up question in which a resistor, or multiple resistors, short out or open. I am then required to calculate the variables in the altered circuit.

    2. Relevant equations
    (Theory question-equations not directly relevant)

    3. The attempt at a solution
    I am unsure of the exact effect, and I have a feeling that my assumptions are incorrect. Please guide me here, let me know if I'm doing it right.

    In the event of a short, I think that the total voltage stays the same and the current is altered.

    In the event of an open circuit (at a specific resistor), I think that the total voltage stays the same, the current becomes zero, and all individual voltages except for the resistor which has opened become zero. That is to say, voltage read across R1 and R2 are zero if R3 opens.

    How am I doing?
  2. jcsd
  3. Oct 31, 2009 #2


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    Science Advisor

    Yes, that sounds OK.

    Resistors that are not carrying current do not have any voltage across them so any voltage from a power source continues unchanged until it meets the open circuit.

    At the open circuit, you would measure the full supply voltage. The other resistors would not have any voltage across them.
  4. Nov 1, 2009 #3
    In addittion to what was said I would add a couple of comments that might not answer your question directly but are useful to know when analyzing these problems.

    1. Remember that the current always takes the path of the LEAST resistance.
    2. Resistors cannot short a circuit because there will always be a voltage drop accross them. You need some sort of wire to create a short circuit. (An element that has resistance of approximately 0 Ohms)
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