567: Urgent Mission

Explain xkcd: It's 'cause you're dumb.
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Urgent Mission
Sure, we could stop dictators and pandemics, but we could also make the signs on every damn diagram make sense.
Title text: Sure, we could stop dictators and pandemics, but we could also make the signs on every damn diagram make sense.


Benjamin Franklin was one of the Founding Fathers of the United States. Aside from uniting most of his country against Britain's heavy-handed rule, he was also an author, printer, musician, politician, postmaster, inventor, scientist, and diplomat. Some of his legacies include bifocals, the Franklin stove, an odometer for a horse-drawn carriage, the almanac, abolitionist ideals, and his image on the $100 bill. For the purposes of this comic, Franklin also created the lightning rod and discovered the fundamentals of electricity, such as positive and negative charges, as well as the conservation of electric charge.

When Franklin first wrote down his notes for electricity, he defined a positive charge as a charge caused by glass rubbing on silk, and a negative charge as a charge left when fur rubs on rubber. This definition for electrical charges still exists today, including in electrical diagrams (as the title text notes). The problem is that as our knowledge of electrical circuitry increased, we realized that the flow of a current, from positive to negative, is not how electrons move in a wire. Rather, it is how the absence of electrons moves in a wire. The flow of electrons themselves go from negative to positive terminals, which is not the first thought that comes to mind in terms of electrical concepts. It's a confusing concept to many fledgling engineers, and one that the time-traveler considers a greater priority. It also adds minus signs in a few physics formulas.


[Cueball steps out of rift. Benjamin Franklin is sitting at his desk with quill and parchment.]
Cueball: Benjamin Franklin?
Franklin: Yes?
Cueball: I bring a message from the future! I don't have much time.
Franklin: What is it?
Cueball: The convention you're setting for electric charge is backward. The one left on glass by silk should be the negative charge.
We were going to use the time machine to prevent the robot apocalypse, but the guy who built it was an electrical engineer.

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The explanation is backwards. Current is defined as the flow of *positive* charge, thus moving from positive to negative terminals. In most cases, the current is actually electrons, which are moving from the negative terminals to the positive. 16:48, 27 June 2013 (UTC)

Hopefully fixed. This was hard to write clearly. 01:43, 11 January 2014 (UTC)

I might be completely mistaken but I've thought that the reason why the positive and negative terminals are assigned as they are originated from observing the electric current passing through the solutions of salt. In the said solutions the current consists of the positively charged ions that get deposited onto the negative electrode, while the positive electrode slowly dissolves. This naturally makes one think that the electric current carries the charged particles from the positive to the negative electrode. Of course it might be that I've completely forgotten what I've been taught in school and gotten everything wrong. 01:50, 29 January 2014 (UTC)

In a circuit, it is the electrons, or the negative charges, that are actually travelling. The positive charges, the nuclei of the material carrying the current, remain fixed. This is opposite to the definition of current, which is defined as the flow of positive charge. In other words, the particles that we define as flowing in a current are not the ones that actually move. Confusing, right? I think what you may be referring to is when a salt solution undergoes electrolysis, the anions (negatively charged part of the salt) travel to the anode (positively charged electrode), and the cations (positively charged particles) travel to the cathode (negatively charged electrode). 06:03, 12 August 2014 (UTC)

Do the same thing with dating conventions, Venerable Bede, and 0 AD. :-) 23:25, 24 August 2015 (UTC)

Ben Franklin just decided to call two opposing charges positive and negative. Blame the guy who decided electrons should be considered negative and protons should be considered positive. 03:28, 20 August 2014 (UTC)

Up until Franklin's experiments with electricity, there was debate as to whether electricity came in two forms, vitreous, as in a glass rod rubbed with silk, and resinous, which other experiments before him was shown to be the one in the rubber rubbed with fur (or amber rubbed with fur, hence the name). Franklin felt there was a single "fluid" which flowed to produce an electric current. He felt that when an object such as the glass rod had an excess of this fluid, it was "positive", and when there was a deficiency of this fluid, the object was "negative". Current flow was the flow of a region of excess "fluid" to a region deficient in it. Unfortunately what actually flowed was electrons and the glass rod form contained excess electrons, not a deficiency of the positively charged fluid. Therefore, HE was the one who started the convention of calling electrons positive. 03:47, 24 August 2014 (UTC)

What we need here is a time machine so we won't waste too much time arguing. -- Weatherlawyer (talk) (please sign your comments with ~~~~)

Wait, I interpereted it completely differently. What if Cueball thought that the Apocalyptic Inventor went evil out of rage over the charge confusion? Trying to make sure that the guy's reason for going evil counts as averting the apocalypse. -[VectorLightning the guest]

At the risk of stating the obvious, the scene is a joke on Terminator (where a time machine was used to fight a robot apocalypse). The time-travelling cueball appears in a Terminator-like bolt. Mountain Hikes (talk) 03:48, 10 December 2015 (UTC)

No, in no way is this even close to the Terminator time travel scenes. 14:22, 6 March 2016 (UTC)