# Search results

1. ### Doppler broadening in a gas

Hi, A very hot gas is enclosed in an oven with a small window. The gas molecules emits radiation at a characteristic wavelength. I assume that because of the thermal motion of the molecules the emitted wavelengths will form a spectrum of some kind (Doppler broadening.) I am trying to derive...
2. ### Statistical physics

Yea, thanks. So if there is N atoms we would have Z_{tot} = Z^N? I think what was confusing me was the fact that I used to think of the heat capacity intuitively as "the amount of energy needed to raise the temperature by 1 degree", and so, the heat capacity approaching 0 seems to imply that...
3. ### Statistical physics

Hi. I'm having trouble with this statistical physics thing again. I am given this exercise: Problem 9 – A spin model In a solid at temperature T the atoms have spin 1 so that the m quantum number takes on the values m = 0, ±1. Due to an interaction with the electrostatic field in the...
4. ### Heat capacity (statistical physics)

Yes, yes, the partition function, I know :-)

6. ### Heat capacity (statistical physics)

Hi. I've just started a course on statistical physics and the first assignment is this: A system possesses 3 energy levels, E_1 = \epsilon, E_2 = 2\epsilon and E_3 = 3\epsilon. The degeneracy of the levels are g(E1) = g(E3) = 1, g(E2) = 2. Find the heat capacity of the system. I've...

Thanks, Tom!
8. ### Line element in spherical coordinates

Hi, I was just reading up on some astrophysics and I saw the line element (general relativity stuff) written in spherical coordinates as: ds^2 = dr^2 + r^2(d\theta^2 + \sin\theta\d\phi) I don't get this. dr is the distance from origo to the given point, so why isn't ds^2 = dr^2 without...
9. ### Calculation of ion radii

Ok, but two electrons in two different atoms can have the same set of quantum numbers without violating the exclusion principle. Why is this not a violation and when does it become a violation? (i.e. how close must the atoms be.) I hope you understand my question.
10. ### Calculation of ion radii

I see. Thanks for taking the time! This is off-topic, but how can we even talk about free space, when electrons are clouds that, theoretically, penetrate all space with some small amplitude. And also, a totally unrelated question: What is the scope of the Pauli exclusion principle. It states...
11. ### Calculation of ion radii

Thanks, man. But how do I know that the cations and anions exactly touch (no free space between them), which is the assumption in your calculation (right?). Aren't they, like, hovering with some free space between them? (this is probably a stupid question :-)
12. ### Calculation of ion radii

Hi, I have yet another problem with this diffraction thing. I have little clue on these questions: e) The radius of the O^2- ion is assumed to be 0.126 nm. By x-ray diffraction experiments the dimensions of the unit cells for MgO, CaO, SrO and BaO has been determined to be 0.4213 nm...
13. ### Bragg diffraction

Thank you very much. My book is Descriptive Inorganic Chemistry by Canham and Overton and I can't find that formula in it.
14. ### Bragg diffraction

I don't know, but man, I'd like to know that formula :!!) I'm having some trouble visualizing this, to say the least.
15. ### Bragg diffraction

Hi, In the solid form FeO, CoO and NiO all has the NaCl-structure (simple cubic). In a series of diffraction experiments with x-rays (\lambda = 0.15406~\text{nm}) one found reflexes from the (111), (200) and (220)-planes with the following \theta-values (\theta is the angle in Bragg's law...
16. ### Introductory nuclear physics

Ok, thanks. That's a pretty stupid exercise. I can't believe it was on last years exam.
17. ### Introductory nuclear physics

Hi. Can anybody help me with this exercise in Introductory Nuclear Physics: One of the magic numbers for nuclei is 28. How many stable isotopes exist with N = 28. (N being the number of neutrons) I have no idea on how to solve this. Thanks.
18. ### Half-harmonic oscillator potential

Wow, that was fast! Thanks. :smile:
19. ### Half-harmonic oscillator potential

I have to find the allowed energies of this potential: $V(x)= \begin{cases} \frac1{2}m\omega^2x^2 & \text{for } x > 0\\ \infty & \text{for } x < 0 \end{cases}$ My suggestion is that all the odd-numbered energies (n = 1, 3, 5...) in the ordinary harmonic osc. potential are...