# Search results

1. ### Dependence of the stress vector on surface orientation

According to Cauchy's stress theorem, the stress vector ##\mathbf{T}^{(\mathbf{n})}## at any point P in a continuum medium associated with a plane with normal unit vector n can be expressed as a function of the stress vectors on the planes perpendicular to the coordinate axes, i.e., in terms of...
2. ### I Problem involving a sequential Stern-Gerlach experiment

Well, with the answers I have read, I think I have managed to clarify myself with this topic (also, looking at vanhees71's articles, it seems that the topic is extensive). Thank you very much :)
3. ### I Problem involving a sequential Stern-Gerlach experiment

Rather than a book, I should have said notes, it's a text written by the professors for the Quantum Mechanics course I am taking (and not a very good one, by the way). I'm sorry, I don't have more information...
4. ### I Problem involving a sequential Stern-Gerlach experiment

The statement of the problem doesn't specify it. I guess that Demystifier is right and that there are two second SG magnets.
5. ### I Problem involving a sequential Stern-Gerlach experiment

Yes, the first beam splits in two after passing through the first S-G, and then both beams pass through the second S-G.
6. ### I Problem involving a sequential Stern-Gerlach experiment

An electron beam with the spin state ## |\psi\rangle = \frac{1}{\sqrt{3}}|+\rangle+\sqrt{\frac{2}{3}}|-\rangle##, where ##\{|+\rangle,|-\rangle\}## is the eigenstates of ##\hat S_z##, passes through a Stern-Gerlach device with the magnetic field oriented in the ##Z## axis. Afterwards, it goes...
7. ### I Parallel transport of a tensor

Oh ok, it is by far much clearer the way you wrote it. Now I see it, thanks!
8. ### I Parallel transport of a tensor

According to my book, the equation that should meet a vector ##\mathbf{v}=v^i\mathbf{e}_i## in order to be parallel-transported in a manifold is: ##v_{, j}^{i}+v^{k} \Gamma_{k j}^{i}=0## Where ##v_{, j}^i## stands for ##\partial{v^i}{\partial y^j}##, that is, the partial derivative of the...
9. ### I Showing that the determinant of the metric tensor is a tensor density

Ok, these were just the "tricks" I was looking for, thank you very much!
10. ### I Derivation of the contravariant form for the Levi-Civita tensor

The covariant form for the Levi-Civita is defined as ##\varepsilon_{i,j,k}:=\sqrt{g}\epsilon_{i,j,k}##. I want to show from this definition that it's contravariant form is given by ##\varepsilon^{i,j,k}=\frac{1}{\sqrt{g}}\epsilon^{i,j,k}##. My attempt What I have tried is to express this...
11. ### I Showing that the determinant of the metric tensor is a tensor density

I'm trying to show that the determinant ##g \equiv \det(g_{ij})## of the metric tensor is a tensor density. Therefore, in order to do that, I need to show that the determinant of the metric tensor in the new basis, ##g'##, would be given by...

13. ### I Doubt about the purpose of some elements in tensor calculus

I would like to know what is the utility or purpose for which the elements below were defined in the Tensor Calculus. They are things that I think I understand how they work, but whose purpose I do not see clearly, so I would appreciate if someone could give me some clue about it. Tensors. As...
14. ### I Expressing the vectors of the dual basis with the metric tensor

Okay, thanks, I see that it was the notation that confused me.
15. ### I Expressing the vectors of the dual basis with the metric tensor

Oh, why not? They are written like this in my textbook
16. ### I Expressing the vectors of the dual basis with the metric tensor

I'm trying to understand why it is possible to express vectors ##\mathbf{e}^i## of the dual basis in terms of the vectors ##\mathbf{e}_j## of the original basis through the dual metric tensor ##g^{ij}##, and vice versa, in these ways: ##\mathbf{e}^i=g^{ij}\mathbf{e}_j##...
17. ### I Time derivative of the angular momentum as a cross product

Okay, but does the formula ##\frac{d \boldsymbol{L}}{d t}=\boldsymbol{\Omega} \times \boldsymbol{L}## have any special meaning, being ##\boldsymbol{\Omega}## the angular velocity?
18. ### I Time derivative of the angular momentum as a cross product

I am trying to find the equations of motion of the angular momentum ##\boldsymbol L## for a system consisting of a particle of mass ##m## and magnetic moment ##\boldsymbol{\mu} \equiv \gamma \boldsymbol{L}## in a magnetic field ##\boldsymbol B##. The Hamiltonian of the system is therefore...
19. ### I Change of variables in the Density of States function

Oh ok, I see, thank you very much!
20. ### I Change of variables in the Density of States function

I have a problem where I am given the density of states for a Fermion gas in terms of momentum: ##D(p)dp##. I need to express it in terms of the energy of the energy levels, ##D(\varepsilon)d\varepsilon##, knowing that the gas is relativistic and thus ##\varepsilon=cp##. Replacing ##p## by...
21. ### Potential energy of a system of two punctual charges along the X axis

Ok, thanks, here it is the correct expression: ##E_{p}=E_{p_1}+E_{p_2}=-kQ^2 (\frac{1}{|x+a|}+\frac{1}{|x-a|})##
22. ### Potential energy of a system of two punctual charges along the X axis

Ok, so the expression of the potential energy should then be written in a different manner to avoid negative distances? What would be the equation? I hadn't written it, but the correct result, according to my textbook, should be ##W=\Delta E_{p}=-2 k \frac{Q^{2}}{a}##
23. ### Potential energy of a system of two punctual charges along the X axis

It's true, I was referring to point charges xD
24. ### Potential energy of a system of two punctual charges along the X axis

I have not clear how to solve this problem. Here it is my attempt at a solution: Let the charge at ##-a## be the number one and the one at ##+a## the number two. the potential energy of the punctual charge ##-Q## due to each charge +Q will be then ##E_{pi}=-k \frac{Q^2}{r_i}##, whit ##r_i## the...