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This is a newbie question. Can someone confirm: a resistor on its own is useless. True or false? I mean, I can't do anything with a resistor alone, or is there something that can be done with it?

Sorry, I know the question is too newbie.

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    \$\begingroup\$ It can generate heat. \$\endgroup\$ – kenny Apr 11 '11 at 21:14
  • \$\begingroup\$ What do you mean by "on its own" or "alone"? Even a voltage source or a transistor or anything else is useless if it is really on its own. \$\endgroup\$ – Curd Jan 5 '12 at 13:12
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    \$\begingroup\$ Resistors by themselves are very useful if you're selling small parts cabinets. Akro Mils likes my collection of unused resistors. \$\endgroup\$ – Olin Lathrop Jan 5 '12 at 14:47
  • \$\begingroup\$ @kenny - no it can't, not on its own. \$\endgroup\$ – stevenvh Jul 28 '12 at 15:53
  • \$\begingroup\$ @stevenvh what the anal? \$\endgroup\$ – kenny Jul 28 '12 at 16:01
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Yes, a resistor by itself is useless. It plays an important part in circuits though.

Resistors limit current in your circuit. For example, if you want to light up an LED, you typically can't just connect an LED to a battery because the current is not limited. With a resistor in series with the LED, you can control the current going through the LED. Also, different values of resistors will give you different currents, which also gives you different LED brightnesses.

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    \$\begingroup\$ It is unfortunate this answer was chosen as the accepted one. While what is said is true, it is only one use of a resistor. Resistors in circuits do a lot more than just limit current, but this answer doesn't mention them and gives the impression that current limiting is a resistor's only use. \$\endgroup\$ – Olin Lathrop Jan 9 '12 at 18:50
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Almost everything we have in electronics is useless on its own. What good is a light bulb by itself? With no power source you can't light it. Even with a power source, it is still not all that helpful with out a switch.

Even the more complex things, like a microcontroller, are pretty useless on there own. Even if you have a power source there isn't much purpose of them unless they are connected to other things.

As for focusing on the resistor itself, there are things that it can be useful for when combined with a power source. For example, creating heat. If your goal is to create heat with a very simple component, using a resistor with a power source is a very simple way of doing it.

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    \$\begingroup\$ @MattB., How frustrated I was when I was in the resistor section of digikey and could not find a single light bulb. \$\endgroup\$ – Kortuk Jan 9 '12 at 20:05
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A resistor on its own may be useless, but that doesn't mean that it doesn't do anything! Resistors produce thermal noise. This noise occurs because of the random movement of charge carriers (mainly electrons). It depends on temperature (the higher the temperature, the higher the noise) and on the resistance value (again, the higher the resistance, the higher the noise). This noise, however, is too small to be useful; you can't power a circuit from a resistor, and the variable nature of the voltage doesn't help either.
While not useful as a power source, this thermal noise often plays a role in circuits. It may be amplified with the signal and deteriorate it.
But even in a circuit the resistor generates this noise voltage all by itself.

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  • \$\begingroup\$ The temperatures required to get any noticeable noise produced by the resistors are so high that the resistor would burn first. The thermal noise characteristics are only used to model systems that have equivalent higher noise temperatures. \$\endgroup\$ – Kellenjb Apr 11 '11 at 18:03
  • \$\begingroup\$ Without the resistor, you have the atmosphere acting as a resistor and a matrix for charged particles, which generates thermal noise. \$\endgroup\$ – Potatoswatter Apr 13 '11 at 17:00
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    \$\begingroup\$ Kellenjb - You can't "notice" anything until you add more components (including the person making note), but that doesn't mean it's not there. And at room temperature it can be significant compared to something one might want to notice, such as a weak radio signal. \$\endgroup\$ – Chris Stratton Jan 5 '12 at 14:59
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Taking the question literally (as a lot of the replies seem to), "Can a resistor on its own do anything".

Yes, it can be confused with an inductor (and vice versa), but only if you don't examine it closely :~) - No power source required.

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  • \$\begingroup\$ I don't upvote this answer because it's not useful for the question, but... you've just made my day :-) \$\endgroup\$ – Axeman Jan 5 '12 at 14:11
  • \$\begingroup\$ IMHO it is usefull because it shows how a question can be interpreted. (And hence might teach how a question should be worded better.) \$\endgroup\$ – Wouter van Ooijen Apr 10 '12 at 6:38
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Resistors by themselves are perfectly useful in debugging situations. Ever not have a jumper wire handy so you can beep out a serial cable, or use it as a test lead? I plug a resistor into the cable or breadboard and that becomes the means for connecting my multimeter. Yes, I read on the same end of the wire, not from the other lead. :)

I know this was a bit of a silly answer and it doesn't answer the OP's question in an EE/circuit analysis sense, but in all practicality, I have used resistors like this very often.

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A resistor, on its own, can (perhaps) exist. "Is it useless?" (true or false) is a different question. I find it pleasing (which is useful to me) to find them strewn about, but that requires me to exist as well. I suppose my answer, in that case, would have to be false (because if I am, the resistor isn't alone). Likewise, the further question (can something be done with it?) would probably be no if there was no one to do that something.

If you were looking for more literal non-circuit applications, I've occasionally used them to tie things together (as staples), leave a trace (I wuz here), fill boxes (the one marked "resistors"), and engage in philosophic discussions (Is resistance really futile?).

If you want to talk resistor only circuits (excusing the supply, connecting wires, and meters), they can be quite useful for draining batteries, heating the room, testing voltages / currents under load, and even as decoration (for instance, Stackpole's RMCF2512JT33K0 - Don't be fooled by its digikey image, its quite large and has "333" prominently display on its face).

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It doesn't do exactly nothing: it will generate heat, depending on the current flowing through it -- this is why resistors have a wattage rating.

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    \$\begingroup\$ But it can't generate this heat all by itself; the required power has to be supplied from the outside! \$\endgroup\$ – stevenvh Apr 11 '11 at 17:28
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    \$\begingroup\$ @stevenvh: Yes, but 99% of electronic devices require external power; that doesn't mean they'd be generally considered "useless by themselves". A paper photograph is useless for its normal purpose without a light source (possibly the Sun) and a person to view it, but a paper photograph would normally be considered independently useful (in contrast to e.g. an electronically-stored one or even a slide) \$\endgroup\$ – supercat Apr 11 '11 at 19:44
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You have to define what is usefull and what is useless first. Resistor on it's own (assuming it is connected to a power supply) can only dissipate power and heat up. If that is what you whant then it is usefull on its own.

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Several resistors can add and average. They can also divide. In a sense, they also multiply, but are reduced in scale.

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