this post was submitted on 31 Mar 2025
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Science Memes

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all 46 comments
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[–] [email protected] 1 points 1 day ago

That's revolting.

[–] [email protected] 3 points 1 day ago (2 children)

Love how there are so many actual solutions in The comments

[–] [email protected] 3 points 1 day ago

Bet they're all engineers.

[–] [email protected] 3 points 1 day ago

But not really. At this level of precision, the heat from electricity passing through it would throw off the actual resistance value.

[–] [email protected] 4 points 1 day ago
[–] [email protected] 10 points 1 day ago

This implies a physicist would do anything practical ever

[–] [email protected] 18 points 1 day ago (1 children)

Simple, all you need is a 6 ohm resistor and a 0.18457216 ohm resistor in series.

[–] [email protected] 3 points 1 day ago

No just get a bunch in parallel!

[–] [email protected] 5 points 1 day ago

And no spherical cows either??

[–] [email protected] 13 points 1 day ago (1 children)

A 11.8 and a 13 in parallel is 6.1854838709677 which is 0.01% off from that resistance. Of course even using matched 1% would screw you as soon as someone opens the door.

[–] [email protected] 3 points 1 day ago (1 children)

You could get exactly 6.1854838709677 for an instantaneous moment by heating up a 6ohm resistor.

[–] [email protected] 2 points 1 day ago

So you just need to figure out the precise amount of prewarming, then subsequently cooling in coordination with the circuit's load to make sure it stays at the right temperature?

[–] [email protected] 4 points 1 day ago* (last edited 1 day ago)

miyazaki-laugh just now realizing that I missed this comm actually

[–] [email protected] 27 points 2 days ago* (last edited 1 day ago) (4 children)

I used to make shunt resistors out of a pencil and a piece of paper. Rub pencil all over paper, cut strips to size of required resistance.

EDIT: I mean megaohm resistors not shunt resistors. 20MOhm for DIY theramin.

[–] [email protected] 2 points 1 day ago

That's cool, could you share some photos? The theramin I mean

[–] [email protected] 2 points 1 day ago

This is exactly how high precision resistors are calibrated. A laser is usually used to notch out bits of the resistor to tune it after it's made.

[–] [email protected] 3 points 1 day ago

I made a potentiometer with paper and graphite clay once

[–] [email protected] 9 points 1 day ago

I admire it but also...wtf lol

[–] [email protected] 12 points 2 days ago (1 children)

A 6.2R in parallel with a 2.5K is pretty close.

[–] [email protected] 9 points 2 days ago

Add in a 400k and you're better than most tolerances you can find

[–] [email protected] 64 points 2 days ago (2 children)

First of all, why are they in the chip aisle looking for resistors? Everybody knows they're in the bread aisle...

[–] [email protected] 12 points 2 days ago (1 children)

He's going to make potato chip resistors to get the right number of course.

[–] [email protected] 5 points 1 day ago (1 children)
[–] [email protected] 3 points 1 day ago

Careful, capacitors reduce ripples

[–] [email protected] 33 points 2 days ago

If you're breadboarding this, you've already lost

[–] [email protected] 26 points 2 days ago (1 children)

What's the significance of that number? It's less than 0.1 away from tau, but somehow I doubt that's it...

[–] [email protected] 32 points 2 days ago (1 children)

I assumed the number is not significant, figure it's just supposed to mock the idea that physicists don't know what tolerances are.

[–] [email protected] 1 points 1 day ago

An experimental physicist should know as far as I know meanwhile a real (theoretical) physicist would probably not even touch numbers that have those scary decimals.

[–] [email protected] 26 points 2 days ago (2 children)

There is if you have a potentiometer and a steady enough hand!

[–] [email protected] 3 points 1 day ago (2 children)

Can you even measure that accurately? Like is it physically possible?

[–] [email protected] 3 points 1 day ago* (last edited 1 day ago)

Based on some rough calculations... no. A precision of 0.0000000000001 ohms is 1000x less than the resistance of 1um of copper with a diameter of 1cm (A piece of wire 10,000x wider than it is long). I'm sure a few molecules of air between your contact points would cause more noise in the measurement.

[–] [email protected] 1 points 1 day ago (1 children)

I thought it had to do with physicists working off theoretical calculations finding precise values for the circuit and not realizing that components come in discrete values.

[–] [email protected] 1 points 1 day ago (1 children)

Yeah, but they could just calculate the right mix of parallel and series discrete resistors to get there.

It’s gonna make a long BOM though.

[–] [email protected] 1 points 23 hours ago

Lol, I was actually going to add that but decided it would be too pedantic if I said it myself.

[–] [email protected] 17 points 2 days ago

U probably need a climate controlled box as well.

[–] [email protected] 17 points 2 days ago (3 children)

I'm too dumb for this joke

[–] [email protected] 6 points 1 day ago* (last edited 1 day ago) (2 children)

I think it’s a joke about physicists not understanding tolerances.

I remember hearing an old story about a company buying signs from a contractor. The contractor produced all kinds of things, so it was fairly straightforward to send them the CAD file and stop worrying about it. One manager did an audit, and realized they were paying hundreds of dollars each for these basic signs. They weren’t fancy or anything, and were just signs throughout the facility that got updated regularly. So why the hell were they paying so much for what should have been a simple print job?

After some investigating, the manager discovered it was because the company didn’t want to hire an artist to design the signs; They just had one of their engineers do it. And the engineer who did the design forgot to change their default tolerances from 3/1000 of an inch. So to comply with the order as written, the contractor was busting out calipers and meticulously measuring the spacing and sizing on each letter before it shipped out the door.

[–] [email protected] 1 points 1 day ago

Damn, engineer time isn't cheap either. Contractor was doing pretty well though

[–] oleorun 2 points 1 day ago (1 children)

"Fuck, Jerry, this one is 2/1000 of an inch! Rerun the batch!"

[–] [email protected] 2 points 1 day ago

Wouldn't that be within tolerance of 3‰?

[–] [email protected] 16 points 1 day ago (3 children)

To a mathematician, pi is 3.1415926535897932384626433832795028841971693993

To an engineer, pi is 3

The joke is basically the same, since you get resistors in certain values, and it's necessary to select the value closest to the one you need

[–] [email protected] 1 points 1 day ago* (last edited 1 day ago)

Maybe round it up to 4 just to be safe.......

[–] [email protected] 2 points 1 day ago

To an engineer, pi is 3

No, to an engineer pi is 22/7, 355/113 if your tolerances are really tight. 3 is pi to a theologist, because that's what the Bible uses.

[–] [email protected] 1 points 1 day ago* (last edited 1 day ago)

I mean, depending on your calculations and scale, you might go a little more precise with it. At a diameter of, say, 10m for a semicircular bridge arc, that's a difference of 0.7m.

(For mathematicians, the difference will be 0.00796m and then some I can't be arsed to write out, but compared to the total arc of 15.7m, that'd be a deviation of 0.05% which is basically zero anyway)

[–] [email protected] 18 points 2 days ago* (last edited 2 days ago)

Fixed resistors
https://en.m.wikipedia.org/wiki/Resistor
The TCR of foil resistors is extremely low, and has been further improved over the years. One range of ultra-precision foil resistors offers a TCR of 0.14 ppm/°C, tolerance ±0.005%, long-term stability (1 year) 25 ppm, (3 years) 50 ppm (further improved 5-fold by hermetic sealing), stability under load (2000 hours) 0.03%, thermal EMF 0.1 μV/°C, noise −42 dB, voltage coefficient 0.1 ppm/V, inductance 0.08 μH, capacitance 0.5 pF.

Quantum based resistors :
https://en.m.wikipedia.org/wiki/Quantum_Hall_effect
Quantum Hall effect →
Applications →
Electrical resistance standards :

(...) Later, the 2019 revision of the SI fixed exact values of h and e, resulting in an exact
R~K~ = h/e^2^ = 25812.80745... Ω.

(this is precise to at least 10 significant digits)

Quantum Ampere Standard
https://www.nist.gov/noac/technology/current-and-voltage/quantum-ampere-standard
.
https://www.nist.gov/noac/technology/current-and-voltage

(...) Quantum-based measurements for voltage and current are moving toward greater miniaturization (...)

(there also been research for defining a quantum based volt standard)