Reverse Polarity



"Harley Quinn: holding a raygun Don't come any closer, or I'll... (reads label on her raygun) reverse polarity! Harley Quinn: I don't know... but it always works on Star Quest."
 * Odd look*

- Gotham Girls, "Cold Hands, Cold Heart"

When a major obstacle in a Science Fiction show is resolved purely through the judicious application of Techno Babble, the characters have successfully Reversed the Polarity. It seems that every futuristic gadget or space ship subsystem performs some miraculous function if only you route the power through it backwards. Urban legend has it the expression originated on Doctor Who. In reality, the phrase "Reverse the Polarity" can be traced back at least as far back as a Carl Barks comic in March 1961. However, it was popularized by Doctor Who, as Jon Pertwee asked the writers for a simple piece of Techno Babble he could reliably deliver. The version most associated with the Third Doctor is "reverse the polarity of the neutron flow", although he only said it once during his time as the Doctor.

A type of Applied Phlebotinum, Reversing the Polarity is the be-all end-all technical solution for any problem. Usually only thought of at the very end of the show ("Captain... we could reverse the polarity of the positron toilet and send a stream of charged crap particles toward the Romulans, rather than away..."). It always works. Always.

Of course, you can "reverse the polarity" in real life — just put the battery in the other way round. Doesn't quite have the same effect, though. Most simple powered toy vehicles, electric toothbrushes and other devices that rely on a spinning electric motor will simply run backwards while more complex electronics with a DC power supply may even break or fry the device in question. This is why most "complex" devices nowadays are equipped with diodes, which keep the current from flowing backwards if the polarity is reversed, preventing damage to the main circuitry. Still, Don't Try This At Home, kids!

Reversing the polarity on a car is also possible—some vintage cars, particularly British ones are positive-ground while negative-ground has been the standard worldwide since The Sixties, so if you want to put a modern MP3-compatible stereo in your '59 Morris Minor a car polarity swap is a must.

Besides, it makes the characters in question look a lot less like brilliant scientists when they are (basically) sighing and asking the technician, "Did you plug it in the wrong way again? I mean, seriously. Red cable is positive. How hard can it possibly be to remember?"

Of course you can't do this with neutrons, because they're as electrically neutral as the name suggests, although if we're getting technical, they do have a magnetic polarity. However, if the neutrons are flowing somewhere, reversing the polarity might refer to changing the direction of flow.

Closely related to the Forgotten Superweapon. Also see Techno Babble and Revive Kills Zombie.

Compare to Tim Taylor Technology.

Anime & Manga
"She reversed the polarity of one of the missiles! It's coming right back at us!"
 * This once happened in Pokémon's English dub when Team Rocket tried to get hold of two Luvdisc, and then reverse the polarity to get rid of all of the love in the world. This being Team Rocket, it's pretty much an Affectionate Parody of the trope. The original version just has them wanting the Luvdisc captured for an ongoing Team Rocket project.
 * In Pokémon: Jirachi Wishmaker, Butler makes a machine that is supposed to create a live Groudon from its fossilized remains. When the machine creates an enormous evil monster instead, he is able to make the machine destroy Groudon by simply reversing the direction of the fossil and the levers.
 * Uchuu Senkan Yamato: This was how they got the drill-missile to unscrew itself out of the barrel of the Wave Motion Gun.
 * In Transformers Victory, Braver invents a device that can detect Decepticon brainwaves. During the inevitable battle, he is able to drive them off by actually reversing the polarity.
 * Cowboy Bebop episode "Honky Tonk Woman":

Comic Books
"Gertrude: Relax, people. He's a powerless kid holding a remote control. Victor: I... I flipped this thing's vibranium battery when you weren't looking. If I press one button while the polarity is reversed, it... it won't be pretty. Molly: Yeah, right. Even I know he's tricking, and I dropped out of the fourth grade."
 * Subverted in Runaways: Victor Mancha (who is being held captive by the aforementioned group) attempts to escape by threatening Gertrude York with a remote that has had its "polarity reversed". The other Runaways scoff at the idea.

"Engineer: "I have to de-amp the resistor diodes to reverse the polarity of the potentiometers -- it's simple when you know how!" Dewey: We'll take your word for it, sir."
 * Ironically, it might not be pretty... but really only for the remote. This is one of those things you don't try at home.
 * A Carl Barks comic book in the Disney Ducks Comic Universe is the earliest recorded use of Reverse Polarity as technobabble, dating all the way back to March 1961 (US #33) in "Billions in the Hole".


 * Atomic Robo's solution for sending the Vampires back the Vampire Dimension is to reverse polarity. Shockingly, the experiment that brought them into our world does not have a "reverse" option, causing Robo to declare that the feature is to be strict company policy from then on. Lampshade, thou art hung.
 * In Marvel Comics' adaptation of Transformers: The Movie, the heroes' ship is targeted by Quintesson missiles. Kup's solution is to reverse the polarity, like he did against the Shrikebats of Dromedan. Hot Rod is afraid it will tear the ship apart.
 * Decepticon missiles. And that was right from the movie, not just the adaptation.
 * Buck Rogers. Did it way more than Star Trek ever did, too.
 * In Sonic the Comic Tails states lines involving this a few times, which is unusual since he isn't a child genius in Fleetway's continuity.

Films
""'...until, from the midst of this darkness, a sudden light broke in upon me. A light so brilliant and wondrous and yet so simple. Change the poles from plus to minus and from minus to plus. I alone succeeded in discovering the secret of bestowing life. Nay, even more... I myself became capable of bestowing animation upon lifeless matter!' ...IT - COULD - WORK!!!""
 * Used to defeat energy-eating giant square stompy robot in Kurt Neumann's 1957 Sci Fi film Kronos, Destroyer of the Universe.
 * In Austin Powers in Goldmember, the tractor beam used by Goldmember and Dr. Evil to pull an asteroid to Earth has "Do not reverse polarity" written on a low-tech-looking panel. When Dr. Evil,, does reverse the polarity, the beam destroys the asteroid instead of sending it to Earth.
 * The original 80s Transformers movie: Being pursued by heat seeking missiles, the fleeing heroes reverse polarities, which apparently causes a sorta energy beam to appear beneath their spaceship. The trope is then subverted because, despite the missiles flying straight through said beam, it has absolutely no effect whatsoever.
 * No. They inverted their shield polarity, which caused the missiles to lose the lock and miss the ship.
 * The 2007 Oceans Thirteen had Brad Pitt dismissing Don Cheadle's technobabble by saying, "Becomes magnetized, reverse polarization, I know."
 * Batman: The Movie (1966): "If I could just... reverse the polarity... send out waves... of super-energy!" Highly effective on torpedoes until... "Confound it! The battery is dead!"
 * For reference, he reverses the polarity on his radio. Yes, that's right, he detonates torpedoes by reversing the polarity of his radio. Then again, WWII-vintage missiles could be thwarted with electric shavers, so...
 * In the 1952 British film The Sound Barrier. the hero solved the problem of controlling a supersonic airplane by reversing the flight controls. To increase lift, for example, he pushed the stick forward instead of back as would be expected. The movie does not state whether this also held true for the engine: would you apply more throttle if you wanted less forward thrust? In any case, Major General Chuck Yeager, the man who was actually the first to fly an airplane faster than sound, was asked about this and stated that any such method would result in the pilot's death (in reality, the problem of lack of control in the transonic range was solved in a straightforward manner by creating much larger control surfaces).
 * This does work above about Mach 6. At that speed and higher if you move the control stick of the Space Shuttle to the right the shuttle would actually bank left. Fly By Wire takes care of this for the pilot.
 * Some of the later model Spitfires had problems with this in dives. They increased the size of the ailerons in order to bump the roll rate, but the super-thin elliptical wings weren't stiff enough to handle the increased force imparted by the larger ailerons at high speeds. Applying the ailerons in a dive would result in the ENTIRE WING twisting under the force, causing the plane to roll in the opposite direction that commanded (note that 'Wing Warping' was the original roll control method used by the Wright Brothers). Initially solved by 'clipping' the wing tips and later by stiffening the wings. Other situations can cause this effect, known as 'Control Reversal'.
 * Control reversal is almost always caused by wing warping of one sort or another when it isn't just pilot error or a maintenance mistake (it's not uncommon for home-built aircraft to get a twist in the control cables during maintenance and have one of the controls backward when it's all put back together). When there is supersonic airflow over wings not designed for it, there can be shockwaves that cause momentary control reversals, but they are basically unpredictable and change vastly with very small speed adjustments, because they depend on precisely where and at what angle a shockwave is hitting a control surface.
 * In the original Spy Kids, the heroes force a Heel Face Turn of the titular Spy Kids robots by reversing their alignment polarity. He does this by inverting the binary code. While it probably would stop the robots from attacking, they would be more likely to crash then turn good. Of course, you can Never Say "Die" in a kids film, so...
 * In Young Frankenstein, Frederick reads from his grandfather's book How I Did It:


 * Some fans justify it in that, being at the end of the journal, we don't hear all of it. Basicly what if one neck bolt was positive and the other negative, and the first experiment got them wrong? For the second one, you would reverse the poles and it would then work.
 * In possibly the earliest use of this trope, Frankenstein Meets the Wolf Man (1943), Dr. Frankenstein's journal explains that the practically immortal monster can be killed by attaching him to the machine that gave him life and "changing the poles".
 * The 1963 movie Son of Flubber features a rain machine that does not work until they reverse the polarity.
 * In the 1996 TV movie Gulliver's Travels Gulliver reversed the big magnet in the flying island to counter the plot of the people on the ground to crash the island by using another big magnet that attracts the island.
 * Self-inflicted in Casino Royale 1967 when a henchman with a crude battery-powered pacemaker is unplugged by Joanna Pettet's character. He frantically reconnects himself and gets the leads wrong, running backward at high speed.
 * Apollo 13: Justified. Shortly before re-entry they needed "four more amps" to power up the Command Module. They used a circuit intended to provide power from the Command Module to the Lunar Module to do the opposite.
 * In Superman II, Superman reverses the chamber that takes away Kryptonian powers. Instead of taking away the powers of the person inside the booth, it removes the powers from the three Kryptonians (Zod, Ursa and Non) standing around outside with Lois and Lex Luthor while he was safe inside. Lex Luthor even comments that "He switched it...".
 * Data literally uses the phrase "Reverse the Polarity" concerning the magnetic door in Star Trek Generations. Course, reversing the polarity on a magnetically-controlled door would open it. Go figure.
 * In Ghostbusters, the Ghostbusters defeat Gozer by crossing the energy streams from their proton packs. This, we are informed, will "reverse the particle flow through the gate." Naturally it works.
 * In Cars 2, Holley says this while trying to escape a death trap in the Big Bentley clock tower. On one hand, they at least keep it grounded in reality: once reversed, the only effect is the clock's motor and gear system running in reverse. On the other hand, she does it by shocking the motor with a Taser...
 * Forbidden Planet. Commander Adams orders a subordinate to "Stand by to reverse polarity" during the initial landing on Altair 4.
 * One of the many reasons Fantastic Four was criticized was its wham-tastic use of this trope. Reed is constantly spouting technobabble, and quite literally, his plan to return the Four to normal is to reverse the polarity of the cosmic rays that gave them their powers.

Literature

 * Robert A. Heinlein's Yellow Peril novel Sixth Column features two kinds of Reverse Polarity used with the book's race-specific-Death Ray. The first way turns it in to a health-ray (don't think too hard about that), and the second way lets you use it on non-Asians.
 * Subverted in one of the fiction-chapters of The Science of Discworld. After the Roundworld is transformed into a snowball (Ice Age), the Dean proposes (after four glasses of sherry) to "get Hex to reverse the thaumic flow in the cthonic matrix of the optimized bi-direction octagonate" to fix it. The Archchancellor replies that he would prefer a non-gibberish opinion.
 * Also in Discworld, there's a spell called the "Rite of Ashk Ente" which summons Death to you, in order to partake in his wisdom. Alberto Malich thought that if the spell makes Death go to you, then performing it backwards would make Death go away. However, he soon finds out that there is another way to consider the spell backwards: sending you directly to Death (which, oddly enough, worked out pretty well for him).
 * In Sandy Mitchell's Warhammer 40000 novel Scourge the Heretic, the jury-rigged device to keep a machine going "reversed the polarity of the neutron flow" (a clear Shout-Out to Doctor Who).
 * Considering the amount of tropes invoked and subverted in the book and the fact that the above-mentioned machine simply didn't work due to the tampering, this can probably be considered deliberate.
 * Kemren the "Purple Mage" in Thieves' World generated Mana by means of waterwheels. It gave him a lot of extra power, but running those waterwheels backwards was enough to beat him.
 * In the Star Trek Voyager novel Ragnarok, the aliens of the week are using shields that automatically reverse poliarty whenever something is shot at them. The crew figures out that they can shoot the shields and then reverse polarity so their next shot will ignore the shields.

Live-Action TV
"The Doctor: Really shouldn't take that long to reverse the polarity. Must be out of practice."
 * Similarly, the cast of Mystery Science Theater 3000 once attempted to shake an alien monster off the satellite with a polarity-reversal maneuver; theirs involved an actual car battery and jumper cables. Also, the alien liked it.
 * The CSI New York Season 1 finale had someone actually "reverse the polarity".
 * In episode 17 of the Sakura Taisen TV series, Kohran puzzles over how to make Iris' kohbu properly handle her vast spirit energies, and comes up with an idea that, among other things, reverses the flow of her spirit energy through the regulator crystal.
 * Star Trek: The Original Series
 * In the episode "That Which Survives", Spock orders Scotty to reverse the polarity of a "magnetic probe". Scotty's incredulous, "reverse polarity?!" qualifies as the Trope Namer.
 * In the episode "Obsession", Spock once did this by "cross-circuiting to B". Same thing.
 * Star Trek: The Next Generation
 * Geordi could make the Enterprise do anything by "routing (some piece of Techno Babble) through the main deflector array".
 * Wesley Crusher is famous for reversing the polarity on every damn thing.
 * In the Star Trek: Voyager episode "Drone", Janeway and Seven of Nine thought they could fry a Borg tractor beam by reversing the polarity of Voyager's phaser banks; it looked on-screen like it was about to work, and instead their own phaser array was knocked out.
 * Memory Alpha records a total of at least five instances in which this order was given on the show. In three instances, it was helpful; in two, it was not.
 * In Star Trek: Enterprise, used almost word for word by Malcolm Reed in the episode "Harbinger", when he reversed the polarity on the plasma coils to knock out an alien.
 * Lampshaded in Stargate SG-1 in which Carter's analogue on the parallel show "Wormhole X-treme!" attempts to solve all problems by reversing the polarity.
 * She also did actually get her homemade naqadah reactor working by reversing the polarity of a trinium plate in Learning Curve. "Reversing the polarity" sounded more professional than "aw shit I put it in backwards".
 * And in "200", during a Star Trek parody, Mitchell as The Captain asks Carter to reverse the polarity in an overly dramatic manner.
 * Doctor Who, as mentioned above. Even LESS justified as it is often neutron flow that is reversed—as neutrons are one of the few particles with no electric charge, changing their polarity would do a great big sod all. After a long time of deliberately not using the phrase, the Tenth Doctor once said it Continuity Nod.

"Arthur Rollo: Yes, yes. I know what it's supposed to do. But, uh, how about the other one? The Minus-X? Lillian Stemmler: No problem. To get the Minus-X drug, I only have to reverse the chemical processes inherent in the Plus-X."
 * Doctor Who also provides a rare example of polarity reversal not working. When Nyssa and Tegan are rapidly aged every time the Doctor tried to take off the ship in Mawdryn Undead due to... something or other, the Fifth Doctor attempts to reverse the polarity of the neutron flow. This only causes them to de-age into children. Try not to think about it.
 * The exact same thing happened to the Fourth Doctor, only it was a chicken turning into an egg, and it wasn't a failure—he was making a point about the technology. It Makes Sense in Context.
 * Parodied again in the new-series episode "The Almost People". An  is created. As he tries to process the Doctor's multiple regenerations, he goes a little weird; one point he says the "neutron flow" variety, only a few lines later to say, using Four's voice; "Would you like a jellybaby?" and then, in Eleven's voice, "Reverse the jellybaby of the neutron flow!"
 * The Doctor's sonic screwdriver once had its polarity reversed to turn it into an electromagnet and draw back a heavy bolt.
 * Space Cases: Catalina is having some trouble with the concept from her textbook. "Reverse the polarity of the neutron flow? What's that all about?" Aren't shout outs fun?
 * Paul Chuckle is always using this in Chucklevision. At one point he reverses the polarity of a UV light (which helps plants grow) to shrink his brother Barry.
 * In the second season The Man From UNCLE episode "The Minus-X Affair", THRUSH scientist Lillian Stemmler is developing a pair of drugs. One ("Plus-X") heightens the senses of the recipient to an almost superhuman degree. The other ("Minus-X") is intended to incapacitate its victims. And how is Minus-X made? Obviously:


 * In "The Moonglow Affair", Solo and Kuryakin are poisoned with deadly radiation from a THRUSH ray gun. To cure them, substitute agent April Dancer must obtain the ray gun so that UNCLE scientists can reverse the polarity and shoot our heroes with it again.
 * Reversing the polarity of the Lexx's main drive causes an EMP of sufficient power to fry any circuits on or near the ship.
 * Power Rangers RPM: "Ranger Blue"—Flynn can't morph due to a bug in his morpher that has led to an energy buildup. While Dr. K is unable to work out a solution, Flynn realizes that he can discharge the energy by simply morphing with his activator chip in backwards.
 * In the Mighty Morphin Power Rangers episode "Opposites Attract", the magnet-themed monster did this trick to sabotage the Rangers' weapons. He could also cause a "polarity switch" for individual people and Angel Grove as a whole. What this actually meant apparently involved a Screen Shake and some storm effects.
 * Spoofed in Kyle XY, when Josh tells a drunken Kyle to sober up by "reversing the polarity of his liver". Kyle goes offscreen, vomits, and comes back sober, saying that he took Josh's advice. It's hard to say whether he was joking or not.
 * Eureka solves a lot of problems this way.
 * Blatantly and explicitly so in the season 3 finale, where
 * Reversed polarity is apparently how the anomaly-locking device on Primeval works.
 * In Smallville, a villain with magnetic powers pushes a car at Clark Kent. Clark catches the car, then uses a live wire to electrify it. Somehow, this causes the villain's "repel" to change to "attract", and he's pulled into the car and defeated.
 * In the 1960's Batman episode "Better Luck Next Time", Batman reverses the polarity on his belt communicator in order to create an ultrasonic signal to drive away a tiger. It was shown on March 17, 1966, thus preceding both both the Star Trek: The Original Series and Batman: The Movie examples.
 * In Emergency, there is a factory worker with his arm caught in a feeding hopper of a machine and Dr. Brackett is rushing over to have it amputated to save his life. However while he is en route, the paramedics come up with a better idea: they work with the factory's engineers and rewire the machine to make the hopper work in reverse to free the worker instead. Just as Dr. Brackett arrives, the modification is finished and they are able to free him instantly.
 * In Sliders Season 2, Episode 3: Gillian of the Spirts, Quinn (via a spirit medium, the titular Gillian) instructs Arturo how to fix the timer by reversing the polarity. It might have been brought up other times in the show, I don't know, who cares?

Music

 * A popular filk song, "The USS Make Shit Up" by Voltaire, about the Star Trek series contains a similar line: "Bounce the graviton particle beam / Off the main deflector dish / That's the way we do things, lad / We're making shit up as we wish..."
 * A musical example is in Bob Carlton's -- sorry, William Shakespeare's -- Return to the Forbidden Planet. Before the show starts, the 'crew' or ensemble members walk out and instruct the audience in standard safety procedures for their flight (air masks will deploy from ceiling, use of cell phones will cause the ship to explode, etc.) and end with teaching the audience how to Reverse Polarity themselves—only for an emergency situation, which is highly unlikely, nigh impossible—by putting their hands on their heads and twisting their torsos and heads to and fro. In Act II, of course, polarity needs to be reversed ("But it's not logical!" "Damn your logic! I've got lives to save!") and the audience has to help.
 * As an added bonus, at the end of the show, as the crew and captain prepare to launch back to Earth (singing Born to Be Wild, of course), crew members announce that all is well by calling "Iambics functioning, Pentameters locked in, Hyperboles all off the scale!" and "R.S.C. jettisoned", in jokes all relating to Shakespeare's text, a conceit of language, and the Royal Shakespeare Company, respectively.
 * Many of the posters (and T-shirts) for the show consist of a warning sign saying "WARNING: Do not reverse polarity!", and the playbill warns of the dangers of polarity reversal in space. Note that it is never actually specified what the polarity is reversed on, just that polarity in general is reversed - which makes the joke even more tongue-in-cheek...
 * Pops up in the Rush song "Vital Signs".

Tabletop Games

 * According to the Star Trek d6 RPG sourcebooks, reversing the polarity in different ways on the main deflector array can create a low power phaser, force someone out of warp, and allow you to basically do ANYTHING you could think of. The Main Deflector Array; Swiss Army Weapon of the Federation. In fact players are encouraged to come up with Techno Babble explanations for whatever it is they are trying to do.
 * Magic: The Gathering made a card for "Reverse Polarity"—any damage taken so far that turn from artifacts is retroactively added to your health total. Lampshaded, but most certainly not explained, in that the picture shows a mace acting as a Healing Shiv.
 * The Yu-Gi-Oh Card Game has a similar card: Rainbow Life.
 * Paranoia adventure "'The Yellow Clearance Black Box Blues''. The Maxwell-Effect Moleculokinesic Field Device is basically a Pyrokinesis gun (e.g. it acts like a flamethrower). 50% of the time it fires at reverse polarity and freezes the target.
 * Ghostbusters adventure Hot Rods of the Gods. If a Ghostbusters fires his proton pack at Meera at the same time as Meera shoots at him with the red devolvo ray, it will reverse the polarity. The devolvo beam will affect Meera and the Ghostbuster will evolve into a superior being with increased intelligence and a large head.

Radio

 * Lampshaded nicely in the Doctor Who BBC Radio drama The Ghosts of N-Space, in which the Brigadier jokingly suggests that the (Third) Doctor "Reverse the polarity of the neutron flow", to which the Doctor replies that the Brig knows as well as he does that the phrase is meaningless.
 * The Torchwood radio play "Lost Souls" plays this trope entirely straight, with the world saved from disaster by reversing the polarity of the positron flow. CERN apparently approved the science, and the impression is the writer was delighted to have found a context where the phrase actually made sense.

Videogames
"By reconfiguring the polarity of the daedron fields, it is possible to manipulate and trace the streams in the following cases..."
 * In Freedom Force vs. the Third Reich, Sky King gets his jetpack to work and saves the day after Bullet tells him to reverse the polarity on his neutrino pack. Bullet is from the future and knew this from reading the Sky King comic books written after Sky King got his jetpack to work, but causality sucks anyway.
 * It turns this is the way to reconnect Clockwerk's body in Sly 2.
 * In Ikaruga, polarity reversing is a gameplay mechanic. White polarity absorbs white bullets, and does double damage to black targets. Black polarity does the opposite.
 * Space Quest 5 has you "reverse the phase polarity of the interface grid" multiple times throughout the game.
 * Referenced in Final Fantasy VI. One of the final bosses uses an attack named 'R. Polarity' to reverse the characters.
 * The video game adaptation of the Death Gate novels uses Magi Babble instead of Techno Babble, but the principle remains the same. There's no point to casting a spell that sets you on fire—but reversing the order of the spell runes casts it on your Doppelganger.
 * Star Trek Online actually has a skill called "Reverse Shield Polarity" that causes energy weapons to increase the shields instead of damaging them.
 * At the end of Ratchet and Clank 2,
 * Morrowind makes a reference to this trope in a certain mage's notes:


 * Your Mission Control in Vanquish says this word for word. But in that case, you're just trying to make a Humongous Mecha's giant energy cannon blow up.

Webcomics
"3: Perhaps if we reverse the polarity of-- 2: Oh, that's your answer to everything!"
 * At least Narbonic's Genre Savvy Dave Davenport knows he's appealing to the Theory of Narrative Causality: "Sometimes it helps, for some reason".
 * Referenced in this Penny Arcade comic.
 * Serron suggests reversing the polarity of something.
 * Keychain of Creation has Misho point out the implausibility of this: "SOL DAMNIT THAT SHOULDN'T DO ANYTHING EVEN IF IT IS POSSIBLE!"
 * Lampshaded in Doctor Who Fanfic Webcomic The 10 Doctors.


 * Done here in Exterminatus Now, to shut down the Void. Complete with references to both Star Trek, Ghostbusters, and a lampshade.
 * Used in Gunnerkrigg Court, here. Annie is trying to fake a Relationship-Salvaging Disaster, and her lack of tech-savvy shows.

Web Originals

 * Yaeger has to do this to the Gravity Engine in The Mercury Men to put the moon back in its proper orbit.
 * This is #4 of Cracked's 6 Sci-Fi Movie Conventions (That Need to Die).

Western Animation
"Sam: I'm impressed. Danny: (makes muscles) With my strength? Sam: No. That you knew what reverse polarity was."
 * Reversing the polarity of energy sources was one of the many plot convenient things Penny's computer book could do on Inspector Gadget.
 * IQ in the James Bond Jr. cartoon also reverses the polarity all the time. He once took control of the bad guy's helicopter with a simple remote control and some polarity reversal.
 * One episode had James himself perform probably the most ludicrous variation ever: In the beginning of the episode, James berates IQ for not fixing his digital watch which for some reason has started counting backwards. Later, James is locked in a room with a doomsday device set to go off. What does he do? He uses some pieces of wire to connect the watch to the device's timer and lo and behold, the watch starts working normally and the timer starts counting backwards.
 * It also happened in The Real Ghostbusters all the time, and probably plenty of other cartoons where people tinker with electronics.
 * A particularly memorable from The Real Ghostbusters occurs when some ghosts get their hands on a proton pack—the standard Ghostbuster weapon—and try exacting some revenge. With the Ghostbusters busy elsewhere, it falls to the Ghostbusters' secretary Janine to corral the ghosts. She does this by using tools at hand and no formal technical training whatsoever to reverse a second proton pack's polarity so it will neutralize the ghost's weapon. Then, with a small twist of a screwdriver, she re-reverses the polarity and uses the pack to capture the disarmed ghosts.
 * In another episode where the Ghostbusters are trapped in an old movie studio and about to be blasted with their own packs, Ray reverses the PKE Meter to send signals to ghosts. It causes ghosts of the studio's hero characters to appear and save the day.
 * In an episode of Extreme Ghostbusters, the team was faced with a ghost that multiplied whenever the proton packs were used against it. They overcame this by converting them into electron packs.
 * Justice League episode "Secret Origins": Batman saves the day by "reversing the ion charge" on an alien ship (this also appeared on the first episode of Challenge of the Superfriends, and very similarly).
 * In the Kim Possible episode "Clean Slate", reversing the polarity on a memory-enhancement device causes it to erase Kim's memories.
 * The device adapted to switch heroes and villains between good and evil is even called the "Reverse Polarizer".
 * In The Tick (animation) Vs Reno, Nevada, Arthur is asked to reverse the polarity on a fish magnet. He finds two cables, blue and red, and a box with two similar a big label saying "Observe Correct Polarity. Use AC current", and two colored sockets. Arthur puts the cables in the wrong sockets, which seems to work, despite the obvious AC current issue.
 * In The New Adventures of Superman, reversing the polarity of an electric charge transferred the powers of the episode's villain (and some other guy) back to Superman... After they got them from him through an electric shock.
 * This is the solution to many a kink in Jimmy's machines in Jimmy Neutron, whether it makes sense or not.
 * In Dexter's Laboratory: Ego Trip, all that takes to turn Mandark's stupid dystopia into Dexter's brilliant utopia is to reverse the polarity of the Neurotomic Protocore from negative to positive, with a button.
 * Shows up in the second G.I. Joe miniseries. Apparently, "reversing the polarity" of a pair of antennae just involves making the tips touch.
 * In the very last episode of the original Transformers cartoon, "The Rebirth, Part 3", the heroes by reversing the polarity of Galvatron's rocket thruster.
 * And in "Call of the Primitives", Grimlock manages to stop Tornedron, an energy-eating being, by reversing his energy polarity (by throwing a switch).
 * In Danny Phantom, Danny uses reverse polarity on the Fenton Thermos to close a ghost portal.

"Alien 1 "That would be very complex..." Alien 2 "Nah, just switch the wires in the bottom and use it again.""
 * In Ben 10 Alien Force, this is required to get Ben's hand back from the Null Void after Sunder separates it from the rest of his body.
 * In Megas XLR due to some wire changes, a weapon Coop uses accidentally gives the enemy reflective shielding. Then when he teleports the stabilizer out of the enemy robot it "reverses the polarity" of the shield making the opponents weapons hit itself.
 * South Park spoofs this (spoilered for Squick, not actual plot spoilers):
 * Also used in the episode "Cancelled", when Jeff Goldblume tries to reverse the polarity of the satellite in Cartman's asshole to figure out where the video is being sent.
 * Filmation 1960's versions of DC Universe heroes.
 * Batman episode "How Many Herring In A Wheelbarrow?". To stop the Joker's Solar Mirror from melting Gotham City, Batman must reverse the polarity of the Master Electrodes powering it by hitting them simultaneously with Batarangs. Seriously.
 * Hawkman episode "The Twenty Third Dimension". Hawkman's "quazer" is converted into a Dimension Ray by reversing its polarity.
 * The Atom episode "The House of Doom''. The Atom reverses the polarity of a miniature nuclear battery to turn it into a Self-Destruct Mechanism.
 * In an episode of the original Teenage Mutant Ninja Turtles cartoon, "Enter The Fly", one of Shredder's evil schemes failed because Baxter Stockman "forgot to reverse the polarity of the neutron flow".
 * This is also how Donatello Deus Ex Machina's just about every other episode once all of the hilarity and wacky hijinks have been taken care of.
 * The Amazing Spiez. In "Operation The 50 Ft. Hacker" a device called the Super Soaker Supersizer has its polarity reversed to return Megan and Davey to normal size.
 * An episode of the Men in Black Cartoon had a super-power giving device. How do you undo its effects? To paraphrase:


 * Subverted in the Founding Zombies episode of Johnny Test. When Johnny uses a ray gun to bring the town's Founding Fathers back to life, Susan (or Mary) attempt to stop them by "reversing the polarity" of the gun. However, because they weren't completely alive, it did nothing. Johnny then had them "reverse the reverse polarity thing" to bring back their mothers and "save" the day.
 * In the Real Adventures of Jonny Quest episode "DNA Doomsday," Hadji reverses the polarity of a DNA blob monster, turning it into mush.
 * Transformers Prime uses this as the Autobots' method of blowing up Megatron's space bridge.
 * Superfriends 1973/74 episode "The Shamon U". Professor Shamon reverses the polarity on his giant electromagnet to repel the Batmobile instead of attracting it.
 * The Herculoids episode "Revenge of the Pirates". Zok does it with his laser Eye Beams to neutralize a force field.

Real Life

 * When a phone exchange fails to hang up on a land line, what do you do? Polarity Reversal!
 * A certain model of text message pager made by Motorola and Unication can be cleared from certain faults by removing and re-inserting the single AA battery in reverse to the normal installation for about 15 seconds, then removing it and installing it normally again.
 * Antimatter is normal matter with Reverse Polarity. The charges of protons and electrons are switched.
 * Every particle also spins into the opposite direction as their normal counterpart. Combining both gets you a real-life Yin-Yang Bomb.
 * Technical support sometimes ask people to reverse the wire. Of course, this is just a subtle way of making sure the customer has the danged thing actually plugged in.
 * Most mains-powered electronic devices with ungrounded (2 prong) cords have the neutral side of the cord connected to the case through a small capacitor. This provides a high-pass filtered path to ground on the case. The idea is to allow high frequency (typically RF) noise to be shunted to ground to prevent interference. Back in the days of non-polarized two-prong plugs, there was actually a benefit to reversing the plug to minimize noise. While the line is AC, it is not balanced. One side is grounded. If two audio devices are connected together, it is best if both cases are bonded to the same side of the mains wiring, ideally the grounded side. Otherwise a small AC current is induced in the shield of the interconnecting cables, which in turn induces a hum in the signal wire.
 * Ground noise actually pops up in the modern age, too. VGA cords conduct the damn crap, causing a ground loop (powerstrip-computer-cable-monitor-powerstrip). Monitor/TV noise (generally seen as "waves") is a classical feature. HOWEVER, the best way to fix this is to unground the computer, though you should then avoid touching metal parts of the chassis when plugged in, just in case.
 * Reversing the Polarity of one speaker of a stereo sound system can have real effects. This happens because waveforms that are 180 degrees out of phase will cancel each other out. The listener will usually hear this as weakened bass response. Of course, this only works once: "My stereo sounded much better when I reversed the polarity on the left speaker. I can't wait to hear how much better it will sound when I reverse the right speaker too!"
 * This can also serve as a simple way of converting mono to stereo. Take a mono sound file, put your sound editor into stereo mode, then invert one of the channels. Quick surround sound. Mind you, it only works well with headphones, and if the resulting file is converted to mono again, silence will result.
 * Which is how noise canceling works. Two waves of 180 degrees will cancel each other out. Of course, this only works when the noise is more or less predictable.
 * Live sound reinforcement mixing consoles have a "phase" switch on every input which is really just a Reverse Polarity switch. This is often used when placing two microphones on the same sound source directly facing each other. If there are 2 microphones on a snare drum, one above facing down and a second below facing up, the engineer will usually Reverse Polarity on the bottom mic.
 * Converting a voltage follower with gain into a comparator with hysteresis is as simple as reversing the polarity of the amplifier.
 * In classical Chinese thought, if the Yellow River runs clear when it should be muddy, or muddy when it should be clear or anything that should be Yin is Yang (or vice versa), it is considered an omen that the ruling dynasty has lost the Mandate of Heaven. Reversing the polarity, in other words, is an omen of DOOOM!
 * The Earth literally reverses the polarity of its magnetic field every couple of hundred thousand years. Scientists are not entirely sure what happens to life when it happens, but you can bet it will be the solution to somebody's problem.http://en.wikipedia.org/wiki/Capillary_electrophoresis
 * Similary, the magnetic field of the sun itself rearranges itself so that at any point, in eleven years it'll be the exact same pattern, only backwards (and when it goes another eleven to twenty-two years, it gets back to where it started).
 * Diode will work different depending on the direction of current.
 * Thermal optics can also reverse polarity. Doing so switches between White Hot and Black Hot (Meaning that heat shows up as white or black, respectively.)
 * In an MRI, the spinning dipoles slowly come out of sync with each other over time, which makes it difficult to observe them. The solution is to use a burst of radiation to reverse the polarity of the spin, which means that all the dipoles will sync up again after the same amount of time between the initial burst and the polarity reversal. This process can be repeated until other sources of error eventually overwhelm the signal.
 * DC motors spin in the opposite direction when their power source is reversed.
 * Electrolytic coating. If the given polarity makes a metal condense on the electrode, the reversed current will dissolve it back.
 * Vascular plants get rid of air bubbles in the xylem by reversing the flow of water during the night.
 * In Capillary Electrophoresis, reversing the polarity is necessary to have your sample actually flow to the detector. Otherwise you just lost all of your sample and contaminated the buffer, And That's Terrible.