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How does a resistor "resist" current/potential?

I know it's an elementary question, but I'm sure others are wondering too.

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    \$\begingroup\$ What's inside? A piece of some "sortaconductor" material whose ratio of length to cross section and conductance produces the desired value, with consideration to other properties such as power dissipation, temperature coefficient, inductive side-effects, etc. \$\endgroup\$ – Chris Stratton Aug 5 '11 at 17:08
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    \$\begingroup\$ Resistance is futile. Sorry, had to be said. \$\endgroup\$ – user3624 Aug 5 '11 at 17:26
  • \$\begingroup\$ @David - Ouch, David, that's a bad one. Just admit that you're only doing this because we can't downvote comments! ;-) \$\endgroup\$ – stevenvh Aug 10 '11 at 18:14
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    \$\begingroup\$ @Kevin Vermeer "sortaconductor" is of course not a technical term, just something I made up on the spur of the moment to stress the desired aspect, while avoiding the "semiconductor" term more associated with (though not limited to) nonlinear and active devices. Indeed one can of course make a resistor out of any non-superconducting wire. \$\endgroup\$ – Chris Stratton Aug 10 '11 at 19:28
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    \$\begingroup\$ @Kevin - Yes, but think of all the downvotes it could have had as well! :-) \$\endgroup\$ – stevenvh Aug 11 '11 at 4:44
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Just as it happens I'm reading this application note by Vishay titled "Basics of Linear Fixed Resistors", which explains the construction of PTH and SMT fixed resistors.

Most resistors have a resistive layer on the surface of a non-conductive carrier, either carbon or metal-based or thick film. The resistance value is obtained by laser-cutting lines in the film.

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  • \$\begingroup\$ Just read the first couple of pages. Good information. Just what I was looking for. Thanks! \$\endgroup\$ – Shubham Aug 5 '11 at 17:43
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    \$\begingroup\$ The resistance value is tweaked by the laser for tight-tolerance components. For wider tolerances, resistance is controlled by composition of the material plus controlled deposition. It's a lot cheaper. \$\endgroup\$ – Mike DeSimone Mar 28 '12 at 2:45
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The simplest is just a wirewound resistor. Metals are not perfect conductors, so a long thin piece of wire will have a predictable resistance to it. Cram it inside a little component by wrapping it into a helix.

enter image description here

There are many other types, too, using thin films, etc:

enter image description here

As for what causes resistance, a simple explanation is that it's analogous to friction. It converts electrical energy into heat energy, the same way friction converts mechanical energy into heat energy.

For a more detailed description, you need to get into physics. In metals, like a wire-wound resistor, "the thermal motion of ions is the primary source of scattering of electrons (due to destructive interference of free electron waves on non-correlating potentials of ions), and is thus the prime cause of metal resistance"

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    \$\begingroup\$ There are certainly roles for such resistors, but the relatively low resistance per unit length that prompts the coiled winding means they will have a high inductance for a given resistance, limiting their use (as resistors) to lower frequency applications. Taken to an extreme, there are parts where the inductance is the goal and the resistance the side effect. \$\endgroup\$ – Chris Stratton Aug 5 '11 at 19:03
  • \$\begingroup\$ @Chris: It's a simple type of resistor, so useful for explaining, and the inductance is minimized with things like en.wikipedia.org/wiki/Ayrton-Perry_winding \$\endgroup\$ – endolith Aug 5 '11 at 19:07
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Here is a link which I suppose, will definitely quench your thirst if nothing else has yet.

http://www.ecawa.asn.au/home/jfuller/electronics/resistors.htm

Inside a carbon resistor is a 'ceramic 'core' on which is deposited a spiral carbon 'track'. The track may have been machined, or 'burnt' away with a laser beam.

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