Polarity

The Doctor had experience, most notably in their third incarnation, with reversing polarities, particularly of the neutron flow. (TV: The Sea Devils et al.)
Nyssa observed that the Ergon, a being of the anti-matter universe, would have to reverse its polarity to remain in N-Space. (TV: Arc of Infinity)
In 1979, the Fourth Doctor reversed the polarity on Fyodor Nikolai Kerensky's equipment to reduce a chicken's personal timeline back to being an egg. (TV: City of Death)
Whilst inside the hypersonic soundwave manipulator with Martha Jones, the Tenth Doctor used his sonic screwdriver to reverse the polarity of the device to incapacitate Richard Lazarus. Exiting the chamber, the Doctor commented that it should not have taken so long, going on to suggest that he was "a bit out of practice." (TV: The Lazarus Experiment)
While trying to stabilise into his namesake's form and personality, a Ganger duplicate of the Eleventh Doctor rapidly fluctuated through the earlier incarnations and spontaneously exclaimed "I've reversed the polarity of the neutron flow!" He then mixed sentences together and said, "I've reversed the jelly baby of the neutron flow." (TV: The Almost People)
Meeting the Tenth Doctor England in 1562, the Eleventh Doctor used his sonic screwdriver in an attempt to reverse the polarity of a time fissure, instructing his previous incarnation to do the same. However, the Tenth Doctor found that, while he was reversing the polarity, the Eleventh Doctor was reversing it back again. As such, the two Doctors only succeeded in "confusing" the polarity before the War Doctor came through the fissure. (TV: The Day of the Doctor)
During the Siege of Trenzalore, the Doctor used his sonic screwdriver to send an instruction to the firearm of a wooden Cyberman to reverse the polarity and fire out the back end, resulting in its destruction. (TV: The Time of the Doctor)
Using the Twelfth Doctor's sonic sunglasses, Clara Oswald reversed the polarity of a neural block which the Doctor had intended to use to wipe her memory of him for her protection. When Clara confessed to this, the Doctor voiced his doubt that she was able to do so but considered either alternative before activating the neural block. As it happened, Clara was successful and so the Doctor lost his memory of her. (TV: Hell Bent)
Yasmin Khan suggested to the Thirteenth Doctor that she reverse the polarity of the mirror leading to the Solitract plane. Upon hearing this, the Doctor observed that her companion spoke her language. (TV: It Takes You Away)
Category:Physics from the real world