boris_73

The Official "Quick Question" Thread

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>If you are looking for very strong magnets' date=' you might try

>Neodymium-Iron-Boron permanent magnets. They are probably the strongest

>permanent magnets you can buy. I have seen these magnets attract dollar

>bills (metallic ink) and magnetically suspend liquid oxygen, which is only

>paramagnetic.

>

>Although I am unsure of how you might direct the field (perhaps pole

>pieces), their strength is unbeatable if you can design the gap-magnet

>combination to take advantage of it. [/quote']

 

Cool. Where do i get some?

 

Are they like the ones from a HDD.

 

It says on here to buy them from Edmund Scientific, but thats in the US.

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sorry I seem to have posted all of this in the wrong Thread, it should be in 'Breaking Magnets', not sure how I did that one guys, sorry about that.

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Lance I just pointed out that i could not buy from as Edmund Scientific is in the US and as a result giving me a number of links to sites in the US is not very helpful :)

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to answer your question in post #54, you can get 2 lovely NIB magnets from most HDDs and the older the drive the bigger the magnet as a general rule :)

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well to add to what YT said i can only say in the case of two HDDs, one 14 years old had 4 NIB mags, each one about 1cm across and 0.5cm high.... compared to one which was about 5 years old, that just had two big ones, about 2cm across and 0.8cm high.

 

again, im not saying YT is wrong because i dont know, but from the two ive looked at, that's what ive seen.

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sorry I seem to have posted all of this in the wrong Thread, it should be in 'Breaking Magnets', not sure how I did that one guys, sorry about that.

No, your posts were moved here because you were taking someone else's thread off-topic.

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lol, thats quite funny :D ed thought he'd accidentally posted a few posts in the wrong thread and didnt know how he did it, then he didnt they were moved! :)

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im very confused! I asked YT what NIBS were because he mentioned them in the breaking magnets thread.

 

Im sure your right and all sayo, but it may be helpful to explain to me the situation, as im not sure how this thread is more relevant.

 

and sorry for bringing the Breaking magnets off track

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how do we know where light is? we know it's velocity is c, so shouldn't we have no clue where it is?

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well firstly its massless, so you cant say, right you, ive got you in my pair of photon-tweezers now!

 

also remember QM's HUP (heisenberg uncertainty principle).

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how do we know where light is? we know it's velocity is c, so shouldn't we have no clue where it is?

 

Do you actually ever know where a photon is, unless it has interacted?

 

Anyway, the HUP deals with momentum, not speed. There will be an uncertainty in the energy, and thus the momentum, of any photon.

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when you write a chemical symbol like Mg you could write Mg (s) coz Mg is a solid... H2O is a liquid so (l)? but (aq) is sumin disolved in water... so how would you write H2O (??)..... prob (l) but im not 100% sure!?!?!?

 

I remember seeing H20 (aq) in a text book during A-level chemistry and having a giggle at the pointlessness of it :)

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H2O(l) would have been correct.

 

maybe by H2O(aq) they meant dilluted water? (a water based sollution of Dihydrogen Monoxide).

 

edit: I`m joking btw :)

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i was trying to make an interference pattern for electrons and got stuck.

[math]\lambda=\frac{h}{p}=\frac{h}{\sqrt{2m(E-V®)}}[/math] i may have gotten the equation wrong because i typed it from memory, but it will have little consequence for my question.

 

what is scalar potential?([math]V®[/math])

 

another question: how do I get from [math]\lambda and \omega\to\psi(r,t)[/math]?

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I wasn't sure where to ask this, but I thought that the quick questions thread looked like a suitable place.

 

I recieved marks for a chemistry test recently and only got half marks for all of the questions that I answered with a chemical formula. My teacher has explained that this is because all of the numbers in my formulas are above the letters. (Attached image: "h20 - top.bmp")

 

My teacher says the numbers should go bellow the letters. (Attached image:"h20 - bottom.bmp")

 

But I am not sure that there actually is a correct way to do this and I lost a slab of marks because of this. If I can prove to my teacher that both ways of doing this are correct then I might be able to reclaim lost marks.

 

So, does anyone know if there actually is a rule suggesting that numbers go bellow letters in chemical formulas? I would be very grateful if someone helps me out here. Thanks all.

h20 - top.bmp

h20 - bottom.bmp

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the convention for number use is to use the bottom in a formula, level with when stating the quantity 2H2O (2 parts H2O).

and for above it`s usualy reserved for the valency like in Fe2 or Fe3 (sometimes accompanied by the charge (+ or -).

 

hope that helps a little :)

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The numbers should go at the bottom.... I think that the best thing to do is just to learn from your mistakes!

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[math] X ^aE^b_c [/math]

 

E = element, eg [math] O [/math]= Oxygen,

 

a = atomic weight, ie number of protons + number of nutrons, so [math] ^{16}O [/math] = oxygen with 8 protons (cos thats what defines oxygen) and 8 nutrons (8+8=16); oygen 16 is the most common isotope of oxygen.

 

b = the charge of the atom. so, if we are considering the O ion which has gained 2 eletrons, its charge would be -2, ie [math] ^{16}O^{-2} [/math]

 

as the atomic weight is the standard for oxygen, we dont have to right it (it is assumed that O = atomic weight of 16). so wed just right [math] O^{-2} [/math]. + or - must always be put in.

 

c = the number of atoms present in the molecule, so if we added a hydrogen ion ([math] H^{+1} [/math]), wed get [math] HO^{-1} [/math], or just [math] HO^- [/math]; add another H ion, and wed get [math] H_2O [/math]

 

x = number of mols of the substance: [math] 5H_2O [/math] would be 5 mols of water

 

so yes, it dus have to go down the bottom, or people get confused.

 

[math] H^2O [/math] seems to be describing a compound with the same number of protons as eletrons, consisting of an atom of hydrogen and an atom of oxygen 2, ie atom with 8 protons and, umm, -6 nutrons (6 anti-nutrons?), everyone gets confused, and then u get bad marks.so there

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we know that as gas expands it cools, or heats up when compressed.

we know the Universe is expanding and the universe contains Gas (mostly Hydrogen).

 

Is that why it`s so cold in space?

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To cut a long story short, the second law of thermodynamics dictates that (being so huge and empty) that it must be.

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