COILED RESDISTOR?

[prateeksikka]

hi  all!
i wish to know that if i have a wire piece and i just coil it up.
what do i get an inductance or resistance?

 

[Alun]

The answer is you'd get both inductance and resistance and some capacitance too, the amount of each will depend on the dimensions of the coil, the metal the wire's made of and the frequency.

 

[Kevin Weddle]

One time at this place I worked, they had these waveguide filters that needed to be tuned. The part that you tuned appeared to be a capacitance screw that had a metal outside and a core on the inside. You put the screw into the waveguide and from there you could adjust the protruding capacitance core. Well on some types of these waveguides, the signal that was input to the waveguide through a coaxial type connector was shorted to the metal outside. It turned out that this apparent short was a filter. Just a small wire shorting the inside conductor to the metal outside. I later read in a book that sometimes a shorted piece of coaxial cable could be used as filter with a calculated Q,bandwidth, and resonant frequency.

 

[prateeksikka]

hi kevin!
actually i was asking this because in our school days when we were asked to measure the resistance of a iece of wire our teacher always told us to coil it up.i dont understand even now why ?
what difference does it make?  ;D

 

[ante1]

Hi prateek,

If you just measure the resistance it will not make any difference! However if you where measuring the inductance or the capacitance it would change the value compared to a strait piece of wire.

 

[prateeksikka]

we just used ohms law for it.i guess we generally coil up a wire to get more length into the ckt and hence higher resistance

 

[Alun]

That would only happen if you used an AC supply and it'd be due to the inductance, not the resistance changing.

 

[audioguru2]

In our schooldays when we were asked to measure the resistance of a piece of wire our teacher always told us to coil it up.
I dont understand even now why? What difference does it make?

If it was a very long piece of wire, if it was not coiled then you might be tempted to add long connecting wires to your ohm-meter to connect to the far ends of the wire being measured.
Then you would have quite an error.

 

[prateeksikka]

hi audioguru!
do u mean about the drops in the connecting wires in case the measured wire is long? ;Dyeah that may be the case and also it is inconvenient to handle ;D