timo

No for two reasons: 1) Black Holes are strongly tied to relativity. Newtonian Gravity (which is where the F=GmM/r² comes from) does not describe black holes. 2) Even for a similar construction in Newtonian Gravity (which would be pretty boring without because it didn´t have an event horizont or any other of the interesting effects of a black hole) this would not be true. The actual reason for weightlessless at the center of earth is what s_pepperchin mentioned as "the complete answer": The fact that the parameter M you plug into the equation and therefore also the resultant force approach zero as you come closer to the center. This would not be true in the newtonian analogon of a black hole where M would be constant and the magnitude of the force would increase as you came closer to the center. We have a thread with the "complete answer" in Newtonian Gravity lying around somewhere in these forums (let´s see if I can find it...). In GR, you´d first have to define what you actually mean by "gravity" but you´d most probably run into the "is not defined at the singularity"-problem for any reasonable definition. EDIT: There´s the thread: http://www.scienceforums.net/forums/showthread.php?t=17027 . Not exactly what I was looking for but it should still be an interesting read.

And before the typo gives rise to confusion: It´s [math] 6.022 \cdot 10^{23} [/math], not 6.022*1023

Not sure how obvious it is for you. From the way TeX is used in forums like these, one might think it is for formulas. That´s not true. TeX is for whole articles/presentations/books. Install Miktex, install TeXnicCenter afterwards. Texniccenter should be able to automatically find the miktex installation. Just don´t bother about miktex. You can chose either to output the file as a .ps or .pdf. After successful compilation of the source, there should be a file of that type in the same directory as the source. Just view it with the viewer you normally use for these filetypes (which in windows usually boils down to "double click on it"). No. You can change the settings of texniccenter to add one and the only difference is that without having a viewer specified, you have to manually click on the file created instead of being able to launch the viewer from texniccenter. Hard to say what you did wrong. I barely know what you have done so far (apart from installing). My advise still is to take a latex-source from someone else (I´m cuttently on a windows comp at my partent´s so I have very limited access to my data, otherwise I´d attach one here) and try to compile it. If that works, start learning tex by replacing the text in the source with your text and use the old source as a a guide of what´s possible and how it´s done.

Hg, "very toxic and dangerous".

Strictly speaking (from the physics point of view) ommiting the units is plain dead wrong. It is sometimes done when the units are obvious like in medicine where mmHg simply is the unit normally used for blood pressure. Therefore ... ... is not a good idea. Of course, with a little thinking you might realize that the numbers are most certainly not mmHg but that doesn´t help too much. That´s how I´d write it.

If 1 mmHg = 0.133 kPa, how much kPa would you think 120 mmHg (120 times 1 mmHg) equal? Not sure if I really get your question but perhaps you´re simply making the question harder than it is.

Go for latex. It´s easy to learn by just writing stuff. Get a latex distribution for windows (like miktex), an editor (like TeXnicCenter) and perhaps some simple latex source so you don´t have bother about stuff like chosing the style-format and including the nessecary packages but only plug in your text.

I don´t really know the "concept of before and after" but I can guess what you are talking about: When two events in spacetime can be connected by a path light could take (mirrors allowed, shielding of light not allowed - the definition is not really about light), then you can tell that the two events have a definite time order. If you cannot, than you cannot say so as you will always find a coordinate system in which the the time order will be reversed. For understanding how two events can have a different time order, think of time as a direction in spacetime (the time I´m talking about here actually is - curvature aside). Put two objects on your table. When you look at them you can hopefully tell which one is left of the other. But when you look at the objects from a different direction, the order which of which being left might have changed. It´s not so much different with time. The harder thing within this analogy is to explain why some events will still always have the same time-order. The reason is that the time-direction is not completely arbitrary but I don´t have any good analogy at hand for this right now. As said, the lightspeed-barrier has nothing to do with light. Light just incidently has the property to travel with the velocity of the barrier ... well, and that´s why the barrier is called lightspeed. Absolute zero temperature would be the same even if Lord Kelvin hadn´t become a scientist.

The first thing I´d try to do is looking "superimposed" up in a dictionary but assuming you´re either a native english speaker or translated that term from your native language, you might skip that step. Having looked it up and it being what I assumed I´d say start by asking yourself what the total deviation is when the deviation of osci 1 is x and the deviation of osci 2 is y. Aswering this question gives you the "resultant oscillation".

I had approached the 3rd question slightly differently but it´s about a rough approx so there´s no "the one" way to do it. The 650 kK seem pretty reasonable to me: In semiconductors, the energy gap between valence band and conducting band is in the order of eV (10^-19 J), IIRC. At room temperature, only a tiny fraction of the electrons are in the conducting band, so thermal energies at 300 K are much below that energy gap.

I think a careful analysis of this statement is advisable. It has the potential for new insights.

I´m actually planning to use it as a repository for things that I expect to be repeatedly posting so that I can simply put a link there and maybe tune for the current situation when a topic appears a 2nd time. This is especially interesting for stuff including a lot of equations. Sadly, last time I had a post which I thought might be a good idea putting on WiSci (the question was what the nabla operator in an above post meant) I had deleted my cookies, forgotten my PW and the mail with the new PW took too long to arrive... I still say you should allow edits by unregistered users, btw.

[x] Other. I´m quite happy without a car till now.

Mostly. Strictly speaking the magnitude of the magnetic force is qBv*|sin(a)| where a is the angle between the direction of the magnetic field lines and the movement direction of the electron. But if you´re only interested in the case where the electron moves perpendicular to the field, then your equations are ok.

I can´t see any problem sketching that function except for that your piece of paper lacks a dimension so you can´t plot a R->C (time -> value of wf) function on it. Either plot real and imaginary parts seperately or plot psi². I can´t see how the wavefunction should look the same for both times. At t=0, the exponential factor gives 1 for both, at the other time, the first eigenfunction will be multiplied by -1 and the second by 1 -> I doubt that this results in the same function. EDIT: ^^ And putting that together, the wavefunction will be real-valued for both times, anyways so there´s even less of a problem.

Psi is a superposition of two eigenstates with diferent energies (different n in your case). So you cannot multiply the whole wavefunction by a common phase to get the time-developement.

I fail to find a c_n in the text. But since I have a guess what it´s supposed to be: I think the poblem assumes that you know the (energy-) eigenstates of the particle (after all, they are given - you only have to identify them).

No. [math] \vec \nabla = \left( \begin{array}{c} \frac{\partial}{\partial x} \\ \frac{\partial}{\partial y} \\ \frac{\partial}{\partial z} \end{array} \right) [/math], in the case of cartesian coordinates. Therefore, [math]\vec \nabla \cdot \vec E = \left( \frac{\partial}{\partial x} \ \frac{\partial}{\partial y} \ \frac{\partial}{\partial z} \right) \left( \begin{array}{c} E_x \\ E_y \\ E_z \end{array} \right) = \frac{\partial E_x}{\partial x} + \frac{\partial E_y}{\partial y} + \frac{\partial E_z}{\partial z} [/math] x-hat, y-hat and z-hat were supposed to be the base vectors in Norman Alber´s notation. For more information see: http://en.wikipedia.org/wiki/Del

Sure. Not true in general but true for vector-bosons (so it is true for photons). If the spin-base for your state is {|u>, |d>} where the two base vectors are left-handed and right-handed polarisation, then you can construct a linear polarisation by |state> = (|u> + |d>)/sqrt(2), for example. It´s a pure one-photon state - it´s only not an eigenvector to the helicity operator.

What do you think? And why?

Perhaps you could show HOW this comes out of the Maxwell eqs for a start?

Isn´t Partition Magic a commercial product (by which I mean: "you have to buy it")? You don´t need to have Linux installed to use qtparted. I downloaded a QTParted Live-CD two weeks ago (but I don´t have the link anymore).

No it doesn´t imply it. It´s a terrible pitfall in relativity: When physicists say that the universe expands, this is not meant in the sense of a shockwave of an explosion expanding out through ... well, there you have your first problem: A shockwave expands in/through air. What does the universe expand into when there´s nothing else than the universe? The expansion is usually visualized by a balloon that´s blown up (for later use, let´s place an ant on the balloon). If you paint two points on the balloon and start to blow it up, the distance between the two points will increase even though the points stay on the same place on the balloon. This increase in distance is NOT limited by lightspeed. In this analogy, the radius of the balloon is the time and the very surface of the balloon is space, btw. And it´s only an analogy so don´t stretch it too much or the balloon will burst . Now for the ant mentioned before. The ant can move around on the surface of the balloon freely. But it´s only a small animal so its speed is limited. In fact, it can´t go faster than lightspeed. If you blow up the balloon sufficiently fast, that poor animal will never get from A to B. No, even if you blew up the balloon very slowly (or even not at all), the ant could walk around the surface of the balloon but never leave it. Unless, of course, Mokele stumbles across this thread and points out that some ants can fly - but we´re talking about an ant that moves at lightspeed and this type can´t fly unless someone manages to prove otherwise. Oh, and welcome to SFN. Don´t be afraid, usually you won´t have to bother with overlength-posts - at least not on scientific topics, that is.