this post was submitted on 25 Jun 2025
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xkcd #3106: Farads (imgs.xkcd.com)
submitted 1 week ago* (last edited 6 days ago) by [email protected] to c/[email protected]
 

xkcd #3106: Farads

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/

explainxkcd for #3106

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[–] [email protected] 57 points 1 week ago (10 children)

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.

[–] [email protected] 27 points 1 week ago (9 children)

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.

[–] [email protected] 5 points 6 days ago (1 children)

But kilogram is the base unit

[–] [email protected] 5 points 6 days ago

Of the SI system. The metric system started with cgs (centimeter, gram, second) and evolved from there.

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