Editing 3106: Farads

{{comic
| number    = 3106
| date      = June 23, 2025<!-- this is its official date, though it appeared 'a day late'; or even two days, by some measures -->
| title     = Farads
| image     = farads_2x.png
| imagesize = 677x253px
| noexpand  = true
| titletext = 'This HAZMAT container contains radioactive material with activity of one becquerel.' 'So, like, a single banana slice?'
}}

==Explanation==
In the comic, [[Cueball]] shows off several items that comprise approximately one of a given unit to [[Megan]] and [[White Hat]]. The first three — {{w|Metre|meter}}s, {{w|Pound (mass)|pound}}s and {{w|volt}}s — are all units of which "1" is a not extraordinary amount for an item that can be easily held in the hand. As such, they elicit minimal reaction from Megan and White Hat. A meter (a unit of length) is visually verifiable; a pound (a unit of weight) is easy to hold in the hand; and a volt (V, a unit of electric potential) would cause minimal harm even if discharged. White Hat's remark that the battery "might need a recharge" refers to the fact that 1 V batteries are somewhat uncommon, but a battery with a larger voltage like an {{w|AA battery|AA}}, {{w|C battery|C}} or {{w|D battery|D}} cell (typically up to 1.5 V) might read as 1 V if significantly depleted.

In contrast, 1 {{w|farad}} is an unusually large amount of capacitance. Capacitance is the ability to store charge, a large amount of which could be dangerous. In common use, most consumer electronics use capacitors in the picofarad to millifarad range, and 1 millifarad is already considered a "large" capacitor. A 1-farad capacitor is considered a supercapacitor. Cueball claiming to have a 1 farad capacitor elicits panic from Megan and White Hat, who fear that {{w|Capacitor#Hazards and safety|it could be very dangerous}}.

For the same charging voltage and load/resistance, a larger capacitor won't deliver greater current or instantaneous power than a smaller one, but the total amount of energy and duration of discharge would be proportionally longer. If the capacitor's wires accidentally touch each other or a third piece of metal, an accidental "short circuit" is created, and all of the capacitor's stored energy discharges very quickly. For example, a 1 farad capacitor charged to 10 volts stores 50 joules of energy, and discharging all of that into a copper wire could cause the wire to heat up by a few dozen degrees Celsius faster than the blink of an eye and cause serious burns (see the [https://old.reddit.com/r/xkcd/comments/1ljxvdo/do_i_not_understand_what_a_capacitor_is/mzqg7ug/ calculation]). Large capacitors are often associated with larger voltages and heavy machinery, which can contribute to the feeling of caution around large capacitances.

The title text explores the inverse situation, where “1” of a unit is a very <b>small</b> amount. A {{w|becquerel}} (Bq) amounts to one radioactive atomic decay per second, which is a really low level of radioactivity. As observed, the material in question could be a single slice of a banana (primarily due to the decay of trace {{w|potassium-40}} in the total potassium it contains, a natural proportion of 117 parts per million). Hence, it is both impractical and unnecessary to contain it inside a container for hazardous materials unless the material is dangerous for other reasons (such as corrosiveness, flammability, or overripeness). For comparison, a 70 kg human body itself [https://web.archive.org/web/20200220103556/https://radioactivity.eu.com/site/pages/Activity_Doses.htm has an activity of 8000 Bq], and the 1986 meltdown of the Chernobyl nuclear power plant released [https://pubmed.ncbi.nlm.nih.gov/10628087/ 2×10<sup>18</sup> (that's 2,000,000,000,000,000,000) Bq]! The earlier common unit for radioactivity is the {{w|Curie (unit)|curie}}, originally defined as the decay rate of 1 gram of radium. It has since been redefined to be 3.7×10<sup>10</sup> decays/second, i.e., 37 GBq. Radioactive material emitting 1 curie that is small enough to fit into a container for hazardous materials is dangerous enough that it probably ''should'' be in one. Bananas as a unit of measurement for radiation exposure are also discussed in the [[Radiation]] chart.

==Transcript==
: [Cueball holds a stick while talking with Megan and White Hat.]
: Cueball: This stick is one meter long.
: Megan: Cool.
: White Hat: That's a nice stick.

: [Cueball holds a smallish rock.]
: Cueball: This rock weighs one pound.
: Megan: I'd believe it.
: White Hat: Looks like a normal rock.

: [Cueball holds a small battery.]
: Cueball: This battery is one volt.
: Megan: Seems fine.
: White Hat: Might need a recharge.

: [Cueball holds a capacitor while Megan and White Hat panic.]
: Cueball: This capacitor is one farad.
: Megan: <b><em>Aaaaa! Be careful!!</em></b>
: White Hat: Put it down!!

==Trivia==
Of the three 'normal' unit quantities, the battery gets a comment that it might not necessarily be. Common household versions of {{w|electrochemical cell}} will normally be designed to produce around 1.5 volts (though some fairly common other versions go as low as 1.2&nbsp;V or as high as 2.1&nbsp;V), with single-/multi-cell {{w|List of battery sizes|batteries in general}} often being rated at a simple multiple of that (e.g. 1.5&nbsp;V, 4.5&nbsp;V, 9&nbsp;V, ...). A cell producing nearer just a single volt, as is pointed out, might be significantly discharged and need recharging. If not replacing entirely, having aged due to too many recharges, as it also definitely would if it is a {{w|primary cell}}.

Also, of all four measures, the {{w|Pound (mass)|pound}} is the only non-SI unit given. A mass of 1 {{w|kilogram}} would also not be too odd a weight to have quoted here, being about 2.2 lb, but may not have been chosen due to its relative unfamiliarity to everyday US readers (even compared to the meter<!--?-->), or else because of its {{w|metric prefix}} (the only one of the {{w|SI base unit}}s, even including the {{w|SI derived unit|derived ones}}, to not be a bare unit) and the gram itself perhaps being even less relatable.

This comic was uploaded very late. Despite the normal three-a-week comic schedule having it come out on Monday, June 23, and being listed on [https://xkcd.com/archive/ xkcd's archive list] for that day, it was actually released well into the next day. This is one of very few times other than [[:Category:April Fools' Day comics|April Fools' comics]] that Randall was so late. The next comic, [[3107]], came out well within its nominal day (Wednesday, and not just by US time zones), such that possibly this comic, of all comics in the usual three-a-week cycle, spent the least time as the "latest" comic before being replaced by the next in its cycle.

{{comic discussion}}<noinclude>
[[Category: Comics featuring Cueball]]
[[Category: Comics featuring White Hat]]
[[Category: Comics featuring Megan]]
[[Category: Physics]]