Resistor or Inductor: Exploring Rheostats

[Starwanderer1]

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..

 

[uart]

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.