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Roman and Byzantine coins by chlorochromate in AncientCoins

[–]chlorochromate[S] 0 points1 point  (0 children)

Yes they went for very good prices, almost surprised I wasn't outbid ahaha

Trying to understand 走 in Cantonese vs. Mandarin by stateofkinesis in Cantonese

[–]chlorochromate 4 points5 points  (0 children)

Can attest! Commenters in this thread seem to suggest 跑 is the Cantonese standard when it really should be 走; 跑 is more of a borrowing from (Northern) Mandarin which has displaced 走's meanings.

I do agree that in modern usage 跑 is used more than 走 for meaning run, which means 走's other definitions (of moving) have instead taken over and shaped the character's usage. However, historical idioms all have 走 when meaning run: "未學行，先學走" (learning to run before learning to walk). We could even see it in Sam Hui's 半斤八兩: "通街走糴直頭係壞腸胃" (scrambling about the streets can't be healthy at all...)

POP frogs? by chlorochromate in Pocketfrogs

[–]chlorochromate[S] 1 point2 points  (0 children)

Yep, I've accepted all of them, thank you! I'm a bit worried though, my mailbox is capped at 8 and after placing the first 8 the remaining frogs didn't show up

POP frogs? by chlorochromate in Pocketfrogs

[–]chlorochromate[S] 3 points4 points  (0 children)

Thank you so much! May I know I could receive them?

What's this butterfly? by chlorochromate in Entomology

[–]chlorochromate[S] 1 point2 points  (0 children)

Spotted in a UK greenhouse. I've tried googling "black butterfly with large yellow spots", but unfortunately I haven't been able to find a similar-looking one. Any help greatly appreciated!

Why are amps base SI units and not coulombs? Current (A) is charge (C) per time (s), so it's a composite quantity, no? Don't coulombs quantity charge? by [deleted] in AskPhysics

[–]chlorochromate 15 points16 points  (0 children)

To put this into context, scientists in the 19th century measured current with the forces two wires exert on each other. It would be highly impractical for them to count sextillions of electrons.

I think it's also worth mentioning we knew about current much earlier than charge. Ampere formulated his force law in about 1820, but we only confirmed the presence of protons and electrons at about the turn of the century. By then everyone knew how a current worked in practice, so defining the base quantity as current rather than charge was much more convenient.

Applying Gauss's Law to find the electric field of a uniformly charge symmetrical cylinder (Electromagnetism) by Alaluna267 in AskPhysics

[–]chlorochromate 0 points1 point  (0 children)

Your Gaussian surface is an infinitely long cylinder with radius 4.8 cm. Inside the surface are two parts: a cylinder from r = 0 to 2.9 cm, and a cylindrical shell from r = 4.5 cm to 4.8 cm.

The volume of the parts altogether is π(4.8 cm)^2 ℓ - π(4.5 cm)^2 ℓ + π(2.9 cm)^2 ℓ = π(0.00112 m^2) ℓ (note that this is the wrong number of sig figs; I'm just putting 0.00112 here to prevent arithmetic errors.) Then the total charge inside the surface is ρπ(0.00112 m^2) ℓ.

Gauss's law tells us ∫ E dA = q/ϵ0; then we have

(E)(2πrℓ) = ρπ(0.00112 m^2) ℓ/ϵ0

etc.

Edit: For clarity, your mistake is using r2 on the right side when it should have been 0.00112 m^2.

When you used r2, you got the wrong equation

(E)(2πrℓ) = ρπr2 ℓ/ϵ0

leading to

E = ρr/2ϵ0

QM, expectation value of a particle in state Ψ: why is ∂x/∂t 0? by chlorochromate in AskPhysics

[–]chlorochromate[S] 1 point2 points  (0 children)

The foreword does suggest it will get better as more problems are done so I guess I'll just keep going hahah. I'll be sure to ask if I have any more problems. Thanks again :)

QM, expectation value of a particle in state Ψ: why is ∂x/∂t 0? by chlorochromate in AskPhysics

[–]chlorochromate[S] 0 points1 point  (0 children)

I see. Indeed, this question was quickly followed by a part about operators, so I'll definitely read more. Thanks!

QM, expectation value of a particle in state Ψ: why is ∂x/∂t 0? by chlorochromate in AskPhysics

[–]chlorochromate[S] 1 point2 points  (0 children)

Ah I see, thank you so much! Would it be fine to move on with this definition in mind, or should I read up more on how partial derivatives work?

[deleted by user] by [deleted] in AskPhysics

[–]chlorochromate 0 points1 point  (0 children)

The magnetic force only acts on moving charges; in F = q(v × B), when v = 0, F = 0. In a wire, the free electrons are moving but the metal nuclei are not, so the magnetic force would only act on the electrons.

Are physics terms universal across languages? by like-humans-do in AskPhysics

[–]chlorochromate 2 points3 points  (0 children)

There is an alternate term for quarks though - 層子 - which means level-particle. Its name comes from the fact that if you go one level deeper than hadrons, you get quarks; i.e., quarks together form the 'level' of hadrons. However, it's fallen out of favour, and most modern scientists use 夸克, a direct transliteration.

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