Title text:
‘This HAZMAT container contains radioactive material with activity of one becquerel.’ ‘So, like, a single banana slice?’
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: Aaaaa! Be careful!!
White Hat: Put it down!!
Source: https://xkcd.com/3106/
Their names are Cueball, Megan, and White Hat?
It is my understanding that XKCD’s “characters” are somewhere between an actual character and an archetype. It isn’t clear…and kind of doesn’t matter, if Black Hat is the same guy in every comic or if he’s a different devious schemer in each. Randall hasn’t bothered to name any of them so the community has given them unofficial nicknames.
I remember reading about their names in explainxkcd. I think the only one never named in the comics is Cueball.
For a while, there was a blog, but I don’t think it named any character.
This capacitor will cost around one Bitcoin
We use it to ignite the tokamak.
Only criticism is the use of non-metric weight units when everything else is SI-based.
Wikipedia currently says:
the international avoirdupois pound, […] is legally* defined as exactly 0.45359237 kilograms
So, technically, a pound is a metric weight, only a niche one whose use may or may not be permitted by local regulations.
Similar is true* of the inch, which is defined as precisely 25.4 millimetres.
* The US, UK and a handful of others collectively signed this into their respective laws in 1959. You might think we don’t use the pound in the UK any more but it still shows up often in informal situations. Ditto inches and feet.
Haha that’s a good one
Capacitors are usually in the realm of pico to micro farads
A one farad capacitor charged to a respectable voltage would feel like a doomsday device in your hand
You see low voltage ones for things like memory backup on hi-fi gear. I have some 3F/5v capacitors in an old Technics tiner.
That is why I like supercapacitors.
Wait so this is like one mistake away from turning that stickman into a fried stickman?
Depends on the voltage it’s charged with, but household current would give it more energy than a shotgun has.
Realistically one would not do that unless you were dealing with something industrial. You would use them otherwise for things like dampening lower voltage systems that need a lot of current.
Closer to the danger level of someone holding two exposed wires plugged into the wall.
Would that not leak a ton to the environment? Parasitic capacitance or smth. I ain’t not voltager.
If we’re getting into practical realities it would probably pop and smolder long before it got fully charged. Capacitance is how much charge something will hold per volt. Doesn’t say anything about how much charge it holds before catching on fire. :)
As long as the voltage is high enough, it does not need a whole Farad to wreck havoc. One of the first pranks they played on me in the lab was the “hey, catch” thing with a large, charged capacitor. Yes, I caught it. And I regretted it soon afterwards.
Household current pumped through a full bridge rectifier, that is.
Capacitors don’t seem to do very much with AC Other than attenuate it a bit
Technically correct. The best kind of correct. :)
I basically solved for shotgun, confirmed in was in the ~100V range and disregarded every other consideration for actually doing it.
I’m pretty sure most hand sized capacitors would just pop if you actually tried to put that much in them.Read in electroboom’s voice: FULL BRIDGE RECTIFIER!!!
Actually, they act like a short circuit to high-frequency AC, so it is more like “blow up” (in general case).
Fun thing. Cheap aluminium capacitors do blow up, when you plug them in the wrong way.
Well by attenuate it a bit you mean they pretty much filter ac out if you have the right capacitance and resistance values as capacitors act like low pass filters.
Capacitors can be used to remove ripple from a DC current. Ripple is basically alternating current that is running along a DC current. So, attenuation, I believe, is the correct terminology.
They generally don’t completely get rid of AC, and they don’t perfectly filter it out unless they are perfectly matched for the AC, and even then, I don’t know of any capacitors that are used in lieu of a full-bridge rectifier or half-bridge rectifier to convert AC to DC.
I could very well be wrong. I am far from an electronics expert, But this is what my understanding tells me.
Well youre not far off. They are used to filter ac, not convert it. They act as low-pass filters which means if you have a setup which is a 100khz low-pass filter it means it only lets through frequencies that are under 100khz. There are of course more accurate but complicated ways of explaining this but that is out of scope for this comment. Also nothing is perfect in the real world but you can calculate how much of the signal it lets through.
but you can calculate how much of the signal it lets through.
Shouldn’t that be “noise” instead of “signal”?
AC units have beefy capacitors, right? Do you know in what range, for comparison?
If by AC you mean air conditioner, I just replaced mine with a 50+5uF dual cap @ 370/440 VAC
Still tens to maybe low hundreds of microfarads.
Oh. I thought it would be more impressive, but that’s still orders of magnitude away. Thanks!
And when they are used for air-conditioning units, they are typically boost capacitors, which means they store up a nice amount of juice for when the compressor powers on and needs a sudden rush of energy, but that’s only a very small amount, like you couldn’t crank a car with the amount of energy in these capacitors.
Operation Sundial 2.0, electric boogaloo.
“This magnet has one tesla”
Most neodymium magnets have like 7 Tesla at their surface.
That stucks ;-)
It is not that much though. You could easily make an electromagnet with magnetic flux density of multiple tesla in it’s core.
And you can get 1F capacitors in bulk from China for a few dozen dollars each.
Those things are still dangerous and scary. The 1T magnet way more so than the capacitor.
I used to teach AP physics to kids on the weekends. One asked me why Farads were so big. I had to explain that there’s a fixed ratio between Farads, Volts, and Joules. One of them had to be crazy big or crazy small.
See also Coulombs.
Caps are especially scary because they can develop their own charge through static electricity, so large value caps are often shipped with their terminals tied together.
There’s nothing in the SI system that says ratios have to be between base units. Units that involve mass are defined against the kilogram not the gram.
But kilogram is the base unit
Of the SI system. The metric system started with cgs (centimeter, gram, second) and evolved from there.
You sent me down a freaking rabbit hole, thanks! :)
From what I found is that there is the simple reason that the weird ones are distance, time and weight - the rest I looked into are based on formal non-normalized definitions (including lumen, which surprised me).
My guess is that in depends on where the unit comes from: science or day to day use.
I learned about the Siemens, the Weber and the Gray on the way.
Thanks again!
They were all done by scientists or engineers.
The meter was defined based on what they calculated as 1 millionth of the length of Paris’ meridian.
The second was 1/86400 of a day, which makes sense with the angle/circle nomenclature on the clock.
The gram was initially set to be the mass of 1cm³ of water at 4°C - which is why 1l of water ≈ 1kg.
The concept of length is way older than these definitions, same for weight and so on.
The meter is an awesome example for what I mean: the 1/1000000 wasn’t random. From my understanding it won over the alternatives in dezimal because of it’s relative closeness to an arms length and the definition was used to remove issues in France because of the (metric) fuckton of different measurements for length.
And the second example of yours is even better describing what I meant: it’s just making sense and is practical not a deep scientific reasoning.
And I won’t bliebe that the foot and inch was conceived by anyone who has a scientific approach.
To be clear: you’re right that basically by definition the units were done by professionals. I try to point out that for the more broader used units practical aspects were at least as important (after all it wasn’t a square meter that was used for the gram but a centi of one).
The kilogram is just a thousand grams, so if they’re tied together, they would still be tied together.
Right. 1F = 1C/1V … they could have just as easily said 1kF = 1C/1V. Many things use kg instead of g. You can tie together things other than the unscaled base units. Then they are still tied together but 1F is a more reasonable amount.
However, 1 farad is really goddamn big.
Lol, explainXKCD
Ah, Randall is alive! I kept thinking my bot had broken as it’s so rare for him to miss an upload.
But why pick one pound? The are so many fun units to choose from, only some of which are conveniently sized. How about a stick 1 mile long, or a rock that weights 1 grain?
A rock that weighs one stone (14 lbs).
Or a barleycorn that’s one barleycorn long? Or a really large foot that’s a foot long. Or a chain that’s a chain long?
A chain is 66 feet long.
That’s 2376 barleycorns, or a small bag of grain if you will.
I bet it’s kind of going off of the original SI representation where, like, a foot was the length of the king’s foot, and that was what they had to measure against to make sure everything was accurate.
I’d be the clueless guy in the room. “I’m not familiar with that unit of measurement.”
A capacitor of 1 farad at standard American 120 volts has the energy between 7.62×54 and .50 BMG, and will discharge just as violently.
Great. Now I get to be the “I’m not familiar with that unit of measurement.” guy.
3,291 J (2,427 ft⋅lbf) to 3,400 J (2,508 ft⋅lbf)
The .50 BMG round can produce between 10,000 and 15,000 foot-pounds force (14,000 and 20,000 J), depending on its powder and bullet type, as well as the weapon it is fired from
foot-pounds
Oh, you Americans and your silly made-up units.
Oh you non-Americans and your lack of wheelchair access ramps.
See how stupid and annoying this is?
All units are made up.
I totally agree that imperial units are silly, though. Base 10 is the way things should be.
But then we’d miss the fun of domain specific units, like A barn
Didn’t even need to translate to foot-pounds-force, since .50 BMG was already in freedom-loving units.
