explain xkcd - User contributions [en]

Talk:3106: Farads

2025-06-25T08:14:58Z

Gautee:

Who wrote this description? It's complete nonsense. A capacitor can't throw a stone. A 1 F capacitor is also not remotely dangerous unless it's charged to a high voltage — except that a 1 F capacitor and a 0.01 F capacitor can be charged to essentially the same maximum voltage!

Unlike other units of measure where a single unit is non-extreme, "The capacitance of the Earth's ionosphere with respect to the ground is calculated to be about 1 F." [https://en.wikipedia.org/wiki/Farad] Most capacitors in practical use are measured in pico, nano, or micro farads. 03:04, 25 June 2025 (UTC)

Please note that the pound, shown in panel 2, is not an SI unit. The corresponding SI unit is the kilogram; an item with a mass of one kilogram is still commonplace. [[User:Troy0|Troy0]] ([[User talk:Troy0|talk]]) 03:11, 25 June 2025 (UTC)

When my father was a young engineer, the old guys would haze the new kids by asking them to fetch a "one farad capacitor". But everybody in the lab said "Sorry, I ran out, go ask Fred on the top floor", "Go ask Tom in the basement", "Try Peter's Parts on Vine St", etc--- give the kid a run-around. The joke was: at the time, 1F was likely large than a large garbage can and many hundred (non-SI) pounds. But the world changed, and in recent years you can easily buy 1F @ 16V, about the size of a soup can, to smooth car sound power feeds. --[[User:PRR|PRR]] ([[User talk:PRR|talk]]) 03:27, 25 June 2025 (UTC)

This explanation would benefit from some elaboration on how and why supercapacitors are dangerous. [[Special:Contributions/195.252.226.234|195.252.226.234]] 04:41, 25 June 2025 (UTC)

Funnily enough, the wikipedia page for "Farad" (https://en.wikipedia.org/wiki/Farad) currently has a 1 farad supercapacitator as the title image. It looks pretty unassuming. [[User:Mouse|Mouse]] 08:54, 25 June 2025 (UTC)

Top of the page says June 23 even though it looks like this came out on June 25. Should it be changed? [[Special:Contributions/85.76.9.43|85.76.9.43]] 05:15, 25 June 2025 (UTC)

I agree with [[User:Troy0|Troy0]] that having a non-SI unit in there (1 pound) is incongruous, and it should instead be a sugar crystal weighing 1 gram. [[Special:Contributions/121.98.227.79|121.98.227.79]] 06:52, 25 June 2025 (UTC)

"most consumer electronics use at most a nanofarad" -> nah... Several hundreds of microfarads are quite common. But so are tens-of-picofarad, mostly in HF/RF filters etc. Calculating an average over all capacitors in all consumer electronics makes no sense anyway... But I'd say "Most consumer electronics use capacitors in the picofarad to milifarad range".
"To prevent static electricity from building lethal charge, unused supercapacitors are usually stored and transported with a "keeper", a steel or aluminum bar shorting the terminals." -> Static charge won't change the voltage of a 1 F capacitor much... V=q/C with small q and large C... The shorting is for high voltage capacitors that 'recharge' themselves trough {{w|Dielectric_absorption|dielectric absorption}}... Interesting, but completely different. -- [[User:Gautee|Gautee]] ([[User talk:Gautee|talk]]) 07:52, 25 June 2025 (UTC)

Talk:3106: Farads

2025-06-25T08:00:31Z

Gautee:

Who wrote this description? It's complete nonsense. A capacitor can't throw a stone. A 1 F capacitor is also not remotely dangerous unless it's charged to a high voltage — except that a 1 F capacitor and a 0.01 F capacitor can be charged to essentially the same maximum voltage!

Unlike other units of measure where a single unit is non-extreme, "The capacitance of the Earth's ionosphere with respect to the ground is calculated to be about 1 F." [https://en.wikipedia.org/wiki/Farad] Most capacitors in practical use are measured in pico, nano, or micro farads. 03:04, 25 June 2025 (UTC)

Please note that the pound, shown in panel 2, is not an SI unit. The corresponding SI unit is the kilogram; an item with a mass of one kilogram is still commonplace. [[User:Troy0|Troy0]] ([[User talk:Troy0|talk]]) 03:11, 25 June 2025 (UTC)

When my father was a young engineer, the old guys would haze the new kids by asking them to fetch a "one farad capacitor". But everybody in the lab said "Sorry, I ran out, go ask Fred on the top floor", "Go ask Tom in the basement", "Try Peter's Parts on Vine St", etc--- give the kid a run-around. The joke was: at the time, 1F was likely large than a large garbage can and many hundred (non-SI) pounds. But the world changed, and in recent years you can easily buy 1F @ 16V, about the size of a soup can, to smooth car sound power feeds. --[[User:PRR|PRR]] ([[User talk:PRR|talk]]) 03:27, 25 June 2025 (UTC)

This explanation would benefit from some elaboration on how and why supercapacitors are dangerous. [[Special:Contributions/195.252.226.234|195.252.226.234]] 04:41, 25 June 2025 (UTC)

Funnily enough, the wikipedia page for "Farad" (https://en.wikipedia.org/wiki/Farad) currently has a 1 farad supercapacitator as the title image. It looks pretty unassuming. [[User:Mouse|Mouse]] 08:54, 25 June 2025 (UTC)

Top of the page says June 23 even though it looks like this came out on June 25. Should it be changed? [[Special:Contributions/85.76.9.43|85.76.9.43]] 05:15, 25 June 2025 (UTC)

I agree with [[User:Troy0|Troy0]] that having a non-SI unit in there (1 pound) is incongruous, and it should instead be a sugar crystal weighing 1 gram. [[Special:Contributions/121.98.227.79|121.98.227.79]] 06:52, 25 June 2025 (UTC)

"most consumer electronics use at most a nanofarad" -> nah... Several hundreds of microfarads are quite common. But so are tens-of-picofarad, mostly in HF/RF filters etc. Calculating an average over all capacitors in all consumer electronics makes no sense anyway... But I'd say "Most consumer electronics use capacitors in the picofarad to milifarad range".

"To prevent static electricity from building lethal charge, unused supercapacitors are usually stored and transported with a "keeper", a steel or aluminum bar shorting the terminals." -> Static charge won't change the voltage of a 1 F capacitor much... The shorting is for high voltage capacitors that 'recharge' themselves trough {{w|Dielectric_absorption|dielectric absorption}}... Interesting, but completely different. -- [[User:Gautee|Gautee]] ([[User talk:Gautee|talk]]) 07:52, 25 June 2025 (UTC)

3106: Farads

2025-06-25T07:55:52Z

Gautee: To prevent static electricity from building lethal charge, unused supercapacitors are usually stored and transported with a "keeper", a steel or aluminum bar shorting the terminals. -> Static charge wont change the voltage of a 1F cap much at all...

{{comic
| number = 3106
| date = June 23, 2025
| 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==
{{incomplete|This page was created recently by one Katal. Don't remove this notice too soon.}}
This comic shows Cueball showing off several items that (he claims to) compose approximately one of a given unit, with Megan and White Hat reacting appropriately. The first three – meters, pounds, and volts – are all very common units that everyday people will regularly encounter, and so receive minimal reaction.

Most household batteries are around 1.5V, although 1V batteries do exist {{Actual citation needed}}. As a battery is discharged, the outputted voltage slowly decreases. Since one volt is below what most batteries market themselves as, the battery could be close to being completely drained and should be recharged. If the battery is supposed to operate at higher voltages, it might indicate that the battery had suffered a deep discharge. In this case, the battery may have suffered permanent damage to its capacity to charge and special care should be taken to safely recharge it.

However, 1 {{w|farad}} is really big. In common use, most consumer electronics use capacitors in the picofarad to milifarad range, and 1 milifarad 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 not-unreasonably ask why the hell he's carrying it around and brandishing it in front of them.

Capacitance (C) is the ratio between charge (coulombs or amp-seconds) and electromotive force (V, volts or joules per coulomb). Weight (pounds or newtons) is the ratio between gravitational potential energy (joules) and height (meters). The stone weighs 1 pound or 4.45 newtons. If the 1-farad capacitor is charged to 1 volt, it will hold 1/2 C * V2 or 0.5 joules. If its discharge is used to raise the 4.45 N stone, it will throw the stone 1/8.9 m or about 11 centimeters. This is a hammer blow.

A 1-farad capacitor charged by a 9-volt battery will throw the stone 10 meters high, a sledgehammer blow. A 0.1-farad capacitor intermittently shorted with a screwdriver makes "lightning flashes" that will illuminate a theater.

The title text resumes more ordinary units, albeit on a less common topic. A becquerel amounts to one radioactive decay per second on the atomic level, 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 potassium-40 in the total potassium it contains). Hence, it is both impractical and unnecessary to contain it inside a hazmat container unless the material is dangerous for other reasons (such as corrosiveness or flammability). In comparison, the human body itself [https://web.archive.org/web/20200220103556/https://radioactivity.eu.com/site/pages/Activity_Doses.htm has an activity of 8000 Bq].

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}
: [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: Aaaaa! Be careful!!
: White Hat: Put it down!!

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

3106: Farads

2025-06-25T07:54:39Z

Gautee: 1 nanofarad? Nah, 470 uf is common enough, and so is 100 nF or 10 nf or 18 pf or 4700 uf...

{{comic
| number = 3106
| date = June 23, 2025
| 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==
{{incomplete|This page was created recently by one Katal. Don't remove this notice too soon.}}
This comic shows Cueball showing off several items that (he claims to) compose approximately one of a given unit, with Megan and White Hat reacting appropriately. The first three – meters, pounds, and volts – are all very common units that everyday people will regularly encounter, and so receive minimal reaction.

Most household batteries are around 1.5V, although 1V batteries do exist {{Actual citation needed}}. As a battery is discharged, the outputted voltage slowly decreases. Since one volt is below what most batteries market themselves as, the battery could be close to being completely drained and should be recharged. If the battery is supposed to operate at higher voltages, it might indicate that the battery had suffered a deep discharge. In this case, the battery may have suffered permanent damage to its capacity to charge and special care should be taken to safely recharge it.

However, 1 {{w|farad}} is really big. In common use, most consumer electronics use capacitors in the picofarad to milifarad range, and 1 milifarad 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 not-unreasonably ask why the hell he's carrying it around and brandishing it in front of them.

Capacitance (C) is the ratio between charge (coulombs or amp-seconds) and electromotive force (V, volts or joules per coulomb). Weight (pounds or newtons) is the ratio between gravitational potential energy (joules) and height (meters). The stone weighs 1 pound or 4.45 newtons. If the 1-farad capacitor is charged to 1 volt, it will hold 1/2 C * V2 or 0.5 joules. If its discharge is used to raise the 4.45 N stone, it will throw the stone 1/8.9 m or about 11 centimeters. This is a hammer blow.

A 1-farad capacitor charged by a 9-volt battery will throw the stone 10 meters high, a sledgehammer blow. To prevent static electricity from building lethal charge, unused supercapacitors are usually stored and transported with a "keeper", a steel or aluminum bar shorting the terminals. A 0.1-farad capacitor intermittently shorted with a screwdriver makes "lightning flashes" that will illuminate a theater.

The title text resumes more ordinary units, albeit on a less common topic. A becquerel amounts to one radioactive decay per second on the atomic level, 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 potassium-40 in the total potassium it contains). Hence, it is both impractical and unnecessary to contain it inside a hazmat container unless the material is dangerous for other reasons (such as corrosiveness or flammability). In comparison, the human body itself [https://web.archive.org/web/20200220103556/https://radioactivity.eu.com/site/pages/Activity_Doses.htm has an activity of 8000 Bq].

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}
: [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: Aaaaa! Be careful!!
: White Hat: Put it down!!

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

Talk:3106: Farads

2025-06-25T07:52:18Z

Gautee:

Who wrote this description? It's complete nonsense. A capacitor can't throw a stone. A 1 F capacitor is also not remotely dangerous unless it's charged to a high voltage — except that a 1 F capacitor and a 0.01 F capacitor can be charged to essentially the same maximum voltage!

Unlike other units of measure where a single unit is non-extreme, "The capacitance of the Earth's ionosphere with respect to the ground is calculated to be about 1 F." [https://en.wikipedia.org/wiki/Farad] Most capacitors in practical use are measured in pico, nano, or micro farads. 03:04, 25 June 2025 (UTC)

Please note that the pound, shown in panel 2, is not an SI unit. The corresponding SI unit is the kilogram; an item with a mass of one kilogram is still commonplace. [[User:Troy0|Troy0]] ([[User talk:Troy0|talk]]) 03:11, 25 June 2025 (UTC)

When my father was a young engineer, the old guys would haze the new kids by asking them to fetch a "one farad capacitor". But everybody in the lab said "Sorry, I ran out, go ask Fred on the top floor", "Go ask Tom in the basement", "Try Peter's Parts on Vine St", etc--- give the kid a run-around. The joke was: at the time, 1F was likely large than a large garbage can and many hundred (non-SI) pounds. But the world changed, and in recent years you can easily buy 1F @ 16V, about the size of a soup can, to smooth car sound power feeds. --[[User:PRR|PRR]] ([[User talk:PRR|talk]]) 03:27, 25 June 2025 (UTC)

This explanation would benefit from some elaboration on how and why supercapacitors are dangerous. [[Special:Contributions/195.252.226.234|195.252.226.234]] 04:41, 25 June 2025 (UTC)

Funnily enough, the wikipedia page for "Farad" (https://en.wikipedia.org/wiki/Farad) currently has a 1 farad supercapacitator as the title image. It looks pretty unassuming. [[User:Mouse|Mouse]] 08:54, 25 June 2025 (UTC)

Top of the page says June 23 even though it looks like this came out on June 25. Should it be changed? [[Special:Contributions/85.76.9.43|85.76.9.43]] 05:15, 25 June 2025 (UTC)

I agree with [[User:Troy0|Troy0]] that having a non-SI unit in there (1 pound) is incongruous, and it should instead be a sugar crystal weighing 1 gram. [[Special:Contributions/121.98.227.79|121.98.227.79]] 06:52, 25 June 2025 (UTC)

"most consumer electronics use at most a nanofarad" -> nah... Several hundreds of microfarads are quite common. But so are tens-of-picofarad, mostly in HF/RF filters etc. Calculating an average over all capacitors in all consumer electronics makes no sense anyway... But I'd say "Most consumer electronics use capacitors in the picofarad to milifarad range". -- [[User:Gautee|Gautee]] ([[User talk:Gautee|talk]]) 07:52, 25 June 2025 (UTC)

3106: Farads

2025-06-25T07:47:06Z

Gautee:

{{comic
| number = 3106
| date = June 23, 2025
| 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==
{{incomplete|This page was created recently by one Katal. Don't remove this notice too soon.}}
This comic shows Cueball showing off several items that (he claims to) compose approximately one of a given unit, with Megan and White Hat reacting appropriately. The first three – meters, pounds, and volts – are all very common units that everyday people will regularly encounter, and so receive minimal reaction.

Most household batteries are around 1.5V, although 1V batteries do exist {{Actual citation needed}}. As a battery is discharged, the outputted voltage slowly decreases. Since one volt is below what most batteries market themselves as, the battery could be close to being completely drained and should be recharged. If the battery is supposed to operate at higher voltages, it might indicate that the battery had suffered a deep discharge. In this case, the battery may have suffered permanent damage to its capacity to charge and special care should be taken to safely recharge it.

However, 1 {{w|farad}} is really big. In common use, even millifarads are quite large, and most consumer electronics use at most a nanofarad. A 1-farad capacitor is considered a supercapacitor. Cueball claiming to have a 1-farad capacitor elicits panic from Megan and White Hat, who not-unreasonably ask why the hell he's carrying it around and brandishing it in front of them.

Capacitance (C) is the ratio between charge (coulombs or amp-seconds) and electromotive force (V, volts or joules per coulomb). Weight (pounds or newtons) is the ratio between gravitational potential energy (joules) and height (meters). The stone weighs 1 pound or 4.45 newtons. If the 1-farad capacitor is charged to 1 volt, it will hold 1/2 C * V2 or 0.5 joules. If its discharge is used to raise the 4.45 N stone, it will throw the stone 1/8.9 m or about 11 centimeters. This is a hammer blow.

A 1-farad capacitor charged by a 9-volt battery will throw the stone 10 meters high, a sledgehammer blow. To prevent static electricity from building lethal charge, unused supercapacitors are usually stored and transported with a "keeper", a steel or aluminum bar shorting the terminals. A 0.1-farad capacitor intermittently shorted with a screwdriver makes "lightning flashes" that will illuminate a theater.

The title text resumes more ordinary units, albeit on a less common topic. A becquerel amounts to one radioactive decay per second on the atomic level, 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 potassium-40 in the total potassium it contains). Hence, it is both impractical and unnecessary to contain it inside a hazmat container unless the material is dangerous for other reasons (such as corrosiveness or flammability). In comparison, the human body itself [https://web.archive.org/web/20200220103556/https://radioactivity.eu.com/site/pages/Activity_Doses.htm has an activity of 8000 Bq].

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}
: [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: Aaaaa! Be careful!!
: White Hat: Put it down!!

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