# Reversing the Polarity **URL:** \ **Category:** Factual Questions\ **Created:** [September 4, 2017, 3:11am UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450 "2017-09-04T03:11:44Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Enola\_Straight](https://avatars.discourse-cdn.com/v4/letter/e/dec6dc/32.png) [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)\ **Post date:** [September 4, 2017, 3:11am UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/1 "2017-09-04T03:11:44Z")
In Star Trek, some problem is often solved by reversing the polarity of the the doo-hicky or channeling some-shit through the deflector dish. Anyway, how often in real life does reversing the polarity work? When recording “The Joshua Tree”, U2 came across a newly-invented instrument called the Infinite Guitar: by re-jiggering a set of pick-ups to act as a speaker instead of a microphone, a feed-back loop was created, providing infinite sustain. The timeless classic “With or Without You” was born. Your Examples? ---
**Author:** ![Reply](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/reply/32/15952_2.png) [@Reply](https://boards.straightdope.com/u/Reply)\ **Post date:** [September 4, 2017, 3:29am UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/2 "2017-09-04T03:29:54Z")
Alternating current works on reversing the polarity, no? ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [September 4, 2017, 3:35am UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/3 "2017-09-04T03:35:22Z")
Every Digital Integrated Circuit is made up a whole bunch of switches that are either on or off, depending on the polarity of the gate of the transistor. The microprocessor and other circuits in your computer (and other digital devices) are “reversing polarity” billions and billions of times whenever you use it. ---
**Author:** ![wolfman](https://avatars.discourse-cdn.com/v4/letter/w/a8b319/32.png) [@wolfman](https://boards.straightdope.com/u/wolfman)\ **Post date:** [September 4, 2017, 3:35am UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/4 "2017-09-04T03:35:36Z")
MRIs work by using a magnetic field to alter the Polarity of a certain percentage of Hydrogen atoms, then letting the polarity reset. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [September 4, 2017, 3:49am UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/5 "2017-09-04T03:49:55Z")
The earth’s magnetic field reverses polarity all the (geologic) time. > **[Geomagnetic reversal](https://en.wikipedia.org/wiki/Geomagnetic_reversal)** > > A geomagnetic reversal is a change in a planet's magnetic field such that the positions of magnetic north and magnetic south are interchanged (not to be confused with geographic north and geographic south). The Earth's field has alternated between periods of normal polarity, in which the predominant direction of the field was the same as the present direction, and reverse polarity, in which it was the opposite. These periods are called chrons. > Reversal occurrences are statistically random. There... Just as in Star Trek, this has worked effectively to repel aliens throughout history. In fact, that’s probably where Scotty got the idea. ---
**Author:** ![John\_Mace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_mace/32/185_2.png) [@John\_Mace](https://boards.straightdope.com/u/John_Mace)\ **Post date:** [September 4, 2017, 3:56am UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/6 "2017-09-04T03:56:04Z")
Did they ever “reverse the polarity” in _STtOS_? I seem to recall it being something introduced in the later franchises, but I wouldn’t swear to it. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [September 4, 2017, 4:03am UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/7 "2017-09-04T04:03:33Z")
> [@John\_Mace](#): > > Did they ever “reverse the polarity” in _STtOS_? I seem to recall it being something introduced in the later franchises, but I wouldn’t swear to it. Yes, in _That Which Survives_. But, why is this in GQ? ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [September 4, 2017, 4:03am UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/8 "2017-09-04T04:03:59Z")
> [@John\_Mace](#): > > Did they ever “reverse the polarity” in _STtOS_? I seem to recall it being something introduced in the later franchises, but I wouldn’t swear to it. I don’t know, but it wasn’t just Star Trek. Using his sonic screwdriver to reverse the polarity has long been SOP for Doctor Who. ---
**Author:** ![Riemann](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/riemann/32/3133_2.png) [@Riemann](https://boards.straightdope.com/u/Riemann)\ **Post date:** [September 4, 2017, 4:06am UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/9 "2017-09-04T04:06:28Z")
> [@beowulff](#): > > But, why is this in GQ? I took the GQ to be: are there examples in real life where reversing the polarity of something actually achieves some purpose? ---
**Author:** ![mikecurtis](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mikecurtis/32/3284_2.png) [@mikecurtis](https://boards.straightdope.com/u/mikecurtis)\ **Post date:** [September 4, 2017, 4:10am UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/10 "2017-09-04T04:10:35Z")
the direction an electric motor runs is determined by it’s polarity, want it to run in the opposite direction? Reverse the polarity! [https://woodgears.ca/motors/reversing.html](https://woodgears.ca/motors/reversing.html) mc ---
**Author:** ![AHunter3](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ahunter3/32/368_2.png) [@AHunter3](https://boards.straightdope.com/u/AHunter3)\ **Post date:** [September 4, 2017, 4:59am UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/11 "2017-09-04T04:59:18Z")
When reassembling an engine, I aligned the camshaft and crankshaft gears so that the alignment marks were aimed at each other. Slipped the distributor down into its socket. Bolted on the heads and manifolds and hooked up the gasoline and spark plug wires and so forth and gave it a try. Chugged and coughed and then belched an impressive geyser of flame out of the throat of the carburetor. “I think I need to reverse the polarity”, I said. I had taken a guess as to whether the current top dead center on cylinder #1 was at the end of compression stroke or at the end of power stroke. I’d guessed wrong. Camshafts rotate once for every two rotations of the crankshaft. Knowing you’re at top dead center on your piston doesn’t tell you if the piston was coming up to compress the air-fuel mixture (stroke 2) or coming up to pump away the exhaust fumes (stroke 4). The distributor is driven by the camshaft so it only fires a given cylinder once every four strokes (i.e., once every camshaft rotation), but I’d inserted it 180° off. The spark plugs were firing towards the end of the exhaust stroke which is immediately followed by the intake stroke (with overlap). The stuff being pumped out was unburned air-fuel mixture (since no spark had fired when it should have) so it now ignited just in time for the intake ports to open and toss in more air-fuel mixture and so a flamefront went rushing out both manifolds. Loosen distributor, rotate 180°, reinsert. Retry. Engine catches, thrumms. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [September 4, 2017, 5:44am UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/12 "2017-09-04T05:44:49Z")
> [@Riemann](#): > > I don’t know, but it wasn’t just Star Trek. Using his sonic screwdriver to reverse the polarity has long been SOP for Doctor Who. But it pre-dates that show by a [good while](http://tvtropes.org/pmwiki/pmwiki.php/Main/ReversePolarity) (like about 60 years). I’ve heard of electric clocks that somehow managed to get their polarity reversed and run backwards. You’d think the clocks would have some kind of internal catch to prevent that. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [September 4, 2017, 10:39am UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/13 "2017-09-04T10:39:20Z")
> [@mikecurtis](#): > > the direction an electric motor runs is determined by it’s polarity, want it to run in the opposite direction? Reverse the polarity! > [Reversing single phase induction motors](https://woodgears.ca/motors/reversing.html) > > mc That is only true for permanent magnet DC motors. Series-wound motors will run the same direction regardless of polarity ---
**Author:** ![LSLGuy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lslguy/32/5813_2.png) [@LSLGuy](https://boards.straightdope.com/u/LSLGuy)\ **Post date:** [September 4, 2017, 11:13am UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/14 "2017-09-04T11:13:43Z")
When jump-starting cars, reversing the polarity solves the problem of what to do with the extra $2K you’d carefully saved up for something fun. 😃 ---
**Author:** ![engineer\_comp\_geek](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/engineer_comp_geek/32/504_2.png) [@engineer\_comp\_geek](https://boards.straightdope.com/u/engineer_comp_geek)\ **Post date:** [September 4, 2017, 11:23am UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/15 "2017-09-04T11:23:40Z")
Peltier devices, aka thermoelectric coolers, are reversible. Peltier devices are used as CPU coolers and are also commonly found in portable picnic coolers (the kind that are battery powered or plug into cigarette lighter sockets). They work like itty bitty heat pumps. Run electricity through them, and one side gets hot and the other side gets cold. They are horribly inefficient, so you need something to draw the heat off of the hot side or the whole thing will quickly overheat, but they have no moving parts and can be made fairly small. They were originally designed for space use, providing temperature control in satellites and space probes and such. Reverse the polarity, and the hot side gets cold and the cold side gets hot. They also work in reverse in the sense that if you apply a heat differential across their surfaces, they generate electricity. So you can either apply electricity and make a heat differential, or you can apply a heat differential and make electricity. ---
**Author:** ![Crafter\_Man](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crafter_man/32/458_2.png) [@Crafter\_Man](https://boards.straightdope.com/u/Crafter_Man)\ **Post date:** [September 4, 2017, 12:15pm UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/16 "2017-09-04T12:15:25Z")
> [@Reply](#): > > Alternating current works on reversing the polarity, no? The wall receptacle in your house reverses the polarity of the _voltage_ every 8.33 milliseconds (or every 10 milliseconds if you’re in Europe). What the _current_ does is dependent on the load: - for some loads, the current alternates - for some loads, the current does _not_ alternate - the current might even be zero ---
**Author:** ![pullin](https://avatars.discourse-cdn.com/v4/letter/p/c57346/32.png) [@pullin](https://boards.straightdope.com/u/pullin)\ **Post date:** [September 4, 2017, 12:22pm UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/17 "2017-09-04T12:22:52Z")
From watching TV shows, I think it only works if you crawl through the air ducts first. All problems in the future are solved this way. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [September 4, 2017, 1:32pm UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/18 "2017-09-04T13:32:02Z")
The only time reversing the polarity solves a problem is when the problem was that you had the wrong polarity to begin with. If the Enterprise was working fine before Scotty got his hands on it, then reversing the polarity won’t help. That said, if you reverse the polarity on an incandescent light bulb, it’ll produce anti-photons. (I can’t remember who I stole that from, but it was someone here) ---
**Author:** ![JWT\_Kottekoe](https://avatars.discourse-cdn.com/v4/letter/j/3ec8ea/32.png) [@JWT\_Kottekoe](https://boards.straightdope.com/u/JWT_Kottekoe)\ **Post date:** [September 4, 2017, 1:58pm UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/19 "2017-09-04T13:58:04Z")
> [@Chronos](#): > > it’ll produce anti-photons. a.k.a. “Darkons”. When trying to sleep it is useful to flip the switch and flood the room with darkness. ---
**Author:** ![What\_Exit](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/what_exit/32/10652_2.png) [@What\_Exit](https://boards.straightdope.com/u/What_Exit)\ **Post date:** [September 4, 2017, 2:06pm UTC](https://boards.straightdope.com/t/reversing-the-polarity/795450/20 "2017-09-04T14:06:04Z")
I’m a Computer Programmer by trade, used to be an HVAC mechanic and before that a Navy electrician. On top of that an old time Star Trek and Science Fiction fan and a TVTroper. So I was well aware of the phrase “reversing the polarity” but never had a situation where it came up until last year. I have to support a pair of old Twinax printers. Twinax is a very dated communication cable. So I purchased a devise for the company that connects to the network via Ethernet and then supports up to 8 Twinax devices. It would not worked. Tried 2 different units and many firmware updates. Tried almost every setting, finally tunneled down to a wiring setup mode that allowed changing the pairing of the cables. The button I pushed for this was labeled “reversing the polarity”. [Next page](https://boards.straightdope.com/t/reversing-the-polarity/795450.md?page=2)