567: Urgent Mission

Explain xkcd: It's 'cause you're dumb.
Revision as of 18:59, 21 January 2014 by (talk) (Explanation)
Jump to: navigation, search
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 and abolitionist ideals. He has since been honored with the use of 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 principal of conservation of charge.

When Franklin first wrote down his notes for electricity, he defined a positive charge as one left on a glass rod by rubbing it with silk, and a negative change as one left on rubber by rubbing it with fur. Without realizing it, this meant that he had assigned a negative value to the charge on the electron, later identified as the fundamental carrier of electrical charge.

In an electrical circuit, we envisage the charge to be flowing from positive to negative. This is analogous to energy flowing from a region of high temperature to one of low temperature, or a fluid moving from an area of high pressure to one of low pressure. However, because an electron is negatively charged, the actual flow of electrons is in the opposite direction, from negative to positive. This reversal of the natural expectation has caused unnecessary confusion to many fledgling engineers.

Time-travelling Cueball believes that reversing this decision has a higher priority than, say, avoiding the robot apocalypse. Rubbing a glass rod with silk removes electrons from the rod, and defining the resulting charge of the rod as negative would have thus assigned positive charge to electrons. Nothing, could ever be the same.

This would mean that protons would have been assigned a negative charge, and a different name would have been used for the positron. Negatronic brains, anyone? Of course it is too late to change now. But a time traveler...


[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.

comment.png add a comment! ⋅ comment.png add a topic (use sparingly)! ⋅ Icons-mini-action refresh blue.gif refresh comments!


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)

There was not and should not have been a 0 CE (or AD) year. If there were, there would also have to be a 0 BCE (or BC) year. Sticking two zero years into the numbering system would not only have played havoc with mathematical systems which were incapable of treating zero as anything other than empty or null, but would also have created a historian's headache. Besides, even for those who believe in the Bible, God did not make Jesus "both Lord and Christ" until his ascension. 23:19, 10 December 2019 (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)
For sure it is not a copy of the sphere which appeared in Terminator, which he draws in 2222: Terminator: Dark Fate, but the reference to Robot Apocalypse is a reference to Terminator none the less. But the comic in it self is not mainly a terminator joke. --Kynde (talk) 15:29, 10 December 2019 (UTC)

Those of us in the year 2020 would have preferred using the time machine for stopping pandemics...Mathmannix (talk) 15:00, 21 August 2020 (UTC)