Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Open circuit?

  1. Oct 22, 2005 #1
    The statement, "when a resistor fails, it will normally open." is true.
    But I don't understand:
    when a resistor fails, doesn't that mean that the resistor doesn't work? so doesn't that mean that resistance=0=short circuit?
  2. jcsd
  3. Oct 22, 2005 #2


    User Avatar
    Staff Emeritus
    Science Advisor

    If a resistor burns out so that the counductive material is disrupted, then it is an open circuit with infinite resistance, i.e. conductance = 0.

    If somehow, the resistor short circuits then it has no resistance (and it is then no longer a resistor).
    Last edited: Oct 22, 2005
  4. Oct 22, 2005 #3
    is a failed resistor one that has 0 resistance?
  5. Oct 22, 2005 #4


    User Avatar
    Science Advisor

    A resistor is "failed" when it doesn't provide the amount of resistance it is rated to, whether it be too much or too little.
  6. Oct 22, 2005 #5


    User Avatar
    Science Advisor
    Homework Helper

    That's a good point. Perhaps I can expand on that..
    Resistors are given a tolerance rating, which could be within 1%, 2%, 5%, or 10% of its nominal value. (You will see what I mean by following the link). If your resistor has a tolerance of 1% and it now measure more than that, it fails to meet its specification. Its a bad part and cannot be trusted to hold even its present measured value in a circuit.

    asdf1 said, "when a resistor fails, it will normally open" . A resistor normally heats up as it conducts current. If the resistor is weakened or defective, that heat can cause the resistor to fuse open. Just like a real fuse, the resistor becomes an open circuit.
    Last edited: Oct 22, 2005
  7. Oct 23, 2005 #6
    i see! thanks!!! :)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook