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Switch not operating?

  1. Jan 18, 2007 #1
    1. The problem statement, all variables and given/known data
    A student finds that a set of Chrismas-tree lights do not operate when the switch is turned on. What is the most likely cause of this?

    2. Relevant equations

    3. The attempt at a solution
    There could be a hole somewhere along the circuit.
    There could have been a short circuit. But wouldn't that lead to an explosion of some sort?
    The switch isn't working.
    There could be many possibilities but don't know which is most likely.
  2. jcsd
  3. Jan 18, 2007 #2


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    Staff: Mentor

    Keep in mind that Christmas tree lights are often a set of light bulbs wired in series. Does that help?
  4. Jan 19, 2007 #3
    That would mean when one globe pops, the others will be brighter as the resistance is added but currect is same for all globes.

    Or are you saying, when one pops, the current going into all the other globes will have increased and that is the problem. The globes will only work within a specific range of current and therefore potential difference since R in each globe is fixed?
  5. Jan 19, 2007 #4


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    The bulbs are in series, which means that a the circuit can be consider a single loop, passing through each of the bulbs. So, if one bulb blows, the circuit it broken and hence non of the other bulbs will work.
  6. Jan 19, 2007 #5
    Good one. I actually thought of it but thought it too unrealistic but if you think about it, it's true. If a bulb stops working, the only reason is that current has stopped flowing in its coil. When that happens, it means there is a connection failure and the rest of the bulbs stop receiving current.
  7. Jan 19, 2007 #6


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    Just to clarify the terminology a bit for you. The word "coil" is usually used for an inductor, where the inductance is being used for some purpose in the circuit. The part of a light bulb that glows when you put a current through it is called the "filament". Wouldn't want you to get that marked wrong on your report. o:)
  8. Jan 19, 2007 #7


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    "Unrealistic"!! Have you never had to search through a string of lights trying to find the one bulb that has blown? And God help you if there is more than one bulb bad!
  9. Jan 19, 2007 #8


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    I definitely know that feeling :rofl:
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