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Resistor or Inductor?

  1. May 3, 2010 #1
    Hi!

    A little food for thought for people who like high school physics labs..

    In a standard rheostat(I have seen only the cylindrical one..the question is about rheostats of this shape..), we find a metal wire wound over a cylindrical core. The wire is wound with very closely spaced turns and as we know,it serves as a potential divider.

    With this sort of construction why doesn't it function as an inductor?
    (in any simple DC circuit with a Rh we find the current to rise to the peak instantaneously rather than exponentially as with an inductor, proving that in no way a Rh can act as an inductor)..
    I guess the trick lies in the construction, please apprise me of the same..

    Reply please..
     
  2. jcsd
  3. May 3, 2010 #2

    uart

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    Science Advisor

    Sometimes (though definitely not always) in wire wound resistors you use opposing turns to minimize the inductance. That is you make a turn, then bend the wire 180 degrees, then make the next turn in the opposite direction and so on.

    The above is not always needed however, since the resistance in such a device is very much larger than it would be in a similar dimensioned wound inductor, hence the time constant L/R is very much less (typically thousands of times less) and the device will still sensibly function as resistor over a fair frequency range despite the presence of some inductance.
     
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