Basic Quantum Physics

[MaxCathedral]

What exactly is Quantum Physics?

 

My minor research informs me that it deals with small variations in energy.

 

That the classic model of the atom is wrong.

 

That its very, very hard to understand...lol.

 

Enlighten me with some basic concepts.

[5614]

wow, i could write pages!

 

quantum physics is often referred to as quantum mechanics

 

QM (quantum mechanics) describes many quantum phenomena which classical mechanics (or i spose you could say normal physics) cannot explain or disagrees with.

 

things such as:

uncertainty principle,

angular momentum,

wave-particle duality,

entaglement &

pauli's exclusion principle

are all explained by QM.

 

i would not say a bit of it is very hard to understand, at the same time to know the detailed explanation of every quantum phenomena is effectively impossible! QM is not basics but you can simplify things until you understand them... im just a 15 (almost 16!) year old kid, but i can get the basics of it... ask me about those 5 things i just mentioned and i can give you a description and some info... ask the average 15 year old and they wont have a clue, as a quantum physicist and you'll get essays!

 

QM is complex, but dont let that put you off, take me as an example, i love it, to me QM is amazing, i learn little bits of it here and there and its useful and fascinating.

[blike]

And it's not really the sort of subject you want to learn on an internet forum. I suggest "Quantum: A Guide for the Perplexed" as an entry-level basic introduction to QM. It's got tons of visuals and it's very easy to read.

[5614]

I've learnt everything i know from the internet, find a few trustworthy sources and ya done! that is obviously to a certain extent or level of details... the internet should be sufficient for a while.... although i may see if i can get a copy of some books soon.

 

i find that:

http://wikipedia.org/

or in english:

http://en.wikipedia.org/wiki/Main_Page

is quite good and then there's always google but be careful what you believe, some stuff on the net is crap and sometimes there's just genuine mistakes, like The Times the other day didnt know the difference between an anode and a cathode in a hydrogen cell, that was a few weeks ago!

[MaxCathedral]

I've learnt everything i know from the internet' date=' find a few trustworthy sources and ya done! that is obviously to a certain extent or level of details... the internet should be sufficient for a while.... although i may see if i can get a copy of some books soon.

 

i find that:

http://wikipedia.org/

or in english:

http://en.wikipedia.org/wiki/Main_Page

is quite good and then there's always google but be careful what you believe, some stuff on the net is crap and sometimes there's just genuine mistakes, like The Times the other day didnt know the difference between an anode and a cathode in a hydrogen cell, that was a few weeks ago![/quote']

 

Max: I am gonna go both way..the internet..great source link by the way 5614, and that book you mentioned blike.

 

Thanks guys...

[5614]

and if you have any questions come here.

 

if i know the answer its good practice and if i dont its good learning!

[Tom Mattson]

i find that:

http://wikipedia.org/

or in english:

http://en.wikipedia.org/wiki/Main_Page

 

I'd be really careful about Wikipedia. There is a woman who has been going through it and rewriting vast sections of QM webpages simply because she is anti-QM. There is a warning header at the top of at least one of her articles' date=' but even so I wouldn't put too much stock in this.

 

If you're hunting for info on the internet then I think it is best to stick with ".edu" websites (those are colleges and universities).

 

That said, try this one:

HyperPhysics

 

On the bubble map, click on "Quantum Physics" and go nutty.

[BlackHole]

I believe that it's very difficult to understand the application of mathematics to physical situations in quantum mechanics without knowing elementary physics first (and of course one has to know it very well).

[ydoaPs]

i put this in the quick question thread, but got no response. i hope that i could get help here.

 

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]?

[fuhrerkeebs]

what is scalar potential?(V®)

 

It's just the potential, such as gravitational potential or electromagnetic potential. The negative gradient of the potential is the force, if that helps.

 

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

 

Just fourier transform.

[ydoaPs]

It's just the potential, such as gravitational potential or electromagnetic potential. The negative gradient of the potential is the force, if that helps.

 

so it is the potential for the slowly varying field? like gravitational or electric potential energy?

 

 

Just fourier transform.

can you explain that?

[5614]

can you explain that?

 

Fourier transform:

http://en.wikipedia.org/wiki/Fourier_transform

[ydoaPs]

wow, i have no clue how to do that. is there anyone that would be willing to show how step-by-step?

[Tom Mattson]

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

 

That's what you're supposed to tell us! You can't solve the problem without knowing it. I'm guessing that you're talking about the double slit experiment. If so then you need to integrate the wavefunction over both slits to find the amplitude at the screen. I don't have time to type up the LaTeX code right now' date=' but I'll try to get you started later.

 

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

 

You don't. You solve the Schrodinger equation for a free particle to get the wavefunction.

[ydoaPs]

i was trying to find the wavelength, not the scalar potential. i didn't even know what it is. by fuhrerkeebs' description, it sounds like it is just potential energy.

 

i thought the schrodinger equation for a free particle deals with how the wave acts. isn't the schrodinger equation for a free particle [math]i\hbar\frac{\delta}{{\delta}{t}}\psi(r,t)=-\frac{{\hbar}^2}{2m}\Delta\psi(r,t)[/math]?

[ed84c]

I think thats;

 

[ydoaPs]

well, i was going from memory. i didn't think i would have it totally correct. that still doesn't help me get the wavefuntion.

[fuhrerkeebs]

Yeah, just use the potential energy that you're particle is interacting in. If there your particle is in an electric field, with one electric charge at the origin forming the field, then you would use V=kq/r^2, where k is Coulomb's constant. Same thing goes for any other potential energy. Then, just solve the equation (sometimes it isn't solvable exactly, however, and you're going to have to rely on numerical methods).

[Tom Mattson]

i was trying to find the wavelength' date=' not the scalar potential.

[/quote']

 

I know. That's the question I was answering. More explicitly, you do not find the wavefunction from the wavelength and the angular frequency.

 

i didn't even know what it is. by fuhrerkeebs' description, it sounds like it is just potential energy.

 

Yes, it is the potential energy function that the particle moves in. You should be able to tell what it is from the problem statement.

 

i thought the schrodinger equation for a free particle deals with how the wave acts. isn't the schrodinger equation for a free particle [math]i\hbar\frac{\delta}{{\delta}{t}}\psi(r,t)=\frac{{\hbar}^2}{2m}\Delta\psi(r,t)[/math]?

 

Yes, it does. And that is how you determine the wavefunction itself.

[Tom Mattson]

well' date=' i was going from memory. i didn't think i would have it totally correct.

[/quote']

 

Actually, you did get it correct, except for using the wrong symbol to denote partial differentiation.

 

that still doesn't help me get the wavefuntion.

 

It won't help you until you specify the potential and the boundary conditions.

 

It would help a lot if you would simply post the exact problem statement.