Demagnetize a television picture tube?

Discussion in 'Homework Help' started by pfelectronicstech, Mar 16, 2012.

  1. pfelectronicstech

    Thread Starter Member

    Jan 18, 2012
    178
    4
    This circuit is used to demagnetize a television picture
    tube each time the set is turned on. The coil surrounds the tube and is energized with an alternating current
    that quickly decays to zero over a period of several seconds. Which of the following components would
    you expect to find connected in series with this coil?
    A. A step-up transformer C. A piezoelectric device
    B. A Hall-effect device D. A PTC thermistor

    I think its C, am I correct? Thanks for the help.
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    You are not correct, a hall device is to measure the magnetic field.

    What would be needed to cause a decreasing current in the degausing coil?

    Bertus
     
  3. pfelectronicstech

    Thread Starter Member

    Jan 18, 2012
    178
    4
    Hello Bertus, this is why I posted this question. That is what I thought it was but on my test I was wrong. I answered "hall effect device" and it was graded as wrong. Why would that be?
     
  4. bertus

    Administrator

    Apr 5, 2008
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  5. mlog

    Member

    Feb 11, 2012
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    Which of those answers would make the current decay over time? You already know it's not a hall-effect device. You have left the transformer, the piezo, and the thermistor. Which of the remaining three makes the most sense to you and why?
     
  6. crutschow

    Expert

    Mar 14, 2008
    13,055
    3,245
    Rather an archaic question. ;)
     
  7. pfelectronicstech

    Thread Starter Member

    Jan 18, 2012
    178
    4
    Guys I'm confused here and I agree its an archaic question. I thought it was Hall effects device, we are saying 100% its not right?
    Step up transformer doesn't make any sense to me even though it deals with coils.
    Piezoelectric makes no sense to me either.
    Is it the PTC thermistor? Narrowing it down that is what i am coming up with.
     
  8. pfelectronicstech

    Thread Starter Member

    Jan 18, 2012
    178
    4
    Thank you Bertus, I appreciate that link. It is PTC thermistor. Sometimes I get set on an answer like with "hall effects" and overlook the others. Thanks again for the help.
     
  9. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    You are right now.
    The PTC will increase its resistance (and lower the current) when the part gets warm.
    There will be some equilibrium between the current and the temperature of the PTC.

    Bertus
     
  10. pfelectronicstech

    Thread Starter Member

    Jan 18, 2012
    178
    4
    Excellent and thanks Bertus, appreciate the help. Stay tuned I may need more help in a few weeks or so.
     
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