# Search results

1. ### How do I see if the equations of motion are satisfied?

Homework Statement (a) Calculate the Conserved currents $$K_{\mu \nu \alpha}$$ associated with the global lorentz transformation and express them in terms of energy momentum tensor. (b) Evaluate the currents for $$L=\frac{1}{2}\phi (\Box +m^2)\phi$$. Check that these currents satisfy...
2. ### A What is orientation of a needle shaped spacecraft?

After much thinking I have found that we need to use the equation for tidal forces acting on the spaceship as it approaches the star. and it appears that there is a big difference (a few hundred g's if i remember correctly) in gravitational acceleration between tip of the spaceship and its tail...
3. ### A What is orientation of a needle shaped spacecraft?

this is a small part of a problem on tidal forces and I wasn't sure what the question asks as it seems to me that more information is needed. Am I right or is there something im missing? the question goes as: "A spacecraft approaches a neutron star of radius 10 km and mass 1.5 times mass of...
4. ### Cylinder parallel to a constant external B field

Homework Statement A cylinder of permeability ##\mu## is placed in an external field ##B_0##. find the strength and direction of magnetic field inside the cylinder for: a) when axis of cylinder is parallel to external field. b) when axis of cylinder makes an angle ##\theta _0## with external...
5. ### Finding canonical transformation

I actually couldn't figure out how to edit the question and insert more details into it so I just created another thread at: "https://www.physicsforums.com/threads/canonical-transformation-two-degrees-of-freedom.846585/#post-5309162" and I included my attempt at solution there (I have actually...
6. ### Canonical Transformation (two degrees of freedom)

so using the Hamiltonian equations of motion I have: $$\dot{Q_1}=\frac{\partial H}{\partial P_1}=aP_1 \Longrightarrow \frac{d(q_1^2)}{dt}=2q_1\dot{q_1}=aP_1\\\dot{Q_2}=\frac{\partial H}{\partial P_2}=b \Longrightarrow \dot{q_1}+\dot{q_2}=b\\\dot{P_1}=0\\\dot{P_2}=0$$ So I guess these are the...
7. ### Canonical Transformation (two degrees of freedom)

Homework Statement Point transformation in a system with 2 degrees of freedom is: $$Q_1=q_1^2\\Q_2=q_q+q_2$$ a) find the most general $P_1$ and $P_2$ such that overall transformation is canonical b) Show that for some $P_1$ and $P_2$ the hamiltonain...
8. ### Finding canonical transformation

Homework Statement If in a system with i degrees of freedom the $$Q_i$$ are given what is the best way to proceed for finding the $$P_i$$ so that we have an overall canonical transformation. say for a two degree freedom system we have $$Q_1=q_1^2$$ and $$Q_2=q_1+q_2$$ Homework Equations...
9. ### Collision of two photons using four-momentum

Thank you so much I have found it. it will be as following: the four momentum of system after the collision and creation of two identical particle will be: $$p^{\mu}_T=(2 \gamma mc,0,0,0)$$ now using $$\gamma=1$$ and using the invariance of the square of the total momentum in a reaction we get...
10. ### Collision of two photons using four-momentum

Then how do we do we solve the last part (part d), I thought i was gonna need it for determining the minimum energy.
11. ### Collision of two photons using four-momentum

Can we use the Lorentz boost ti find it? I mean looking for a transformation that makes the spatial components of the total four momentum vanish?
12. ### Collision of two photons using four-momentum

Homework Statement Two photon of energy ##E_1 ## and ## E_2## collide with their trajectory at an angle $\theta$ with respect to each other. a) Total four-momentum before collision? b) square length of 4-momentum in lab frame (LB)and in center of momentum frame (CM)? c) 4-momentum of two photon...
13. ### Separation of variables and potential

Homework Statement A potential satisfies ##\nabla^2 Φ = 0## in the 2d slab ## -\inf < x < \inf ##, ##-b < y < b ##, with boundary conditions ## Φ(x, +b) = +V_s(x)## on the top and ##Φ(x, b) = -V_s(x)## on the bottom, where[/B] ##V_s (x)= -V_0 for -a<x<0## ##V_s (x)=+V_0 for 0<x<a## (a) what...
14. ### Finding potential using Greens function

I have actually found out a way to do it, its not through bessels functions though. but thank you for the help
15. ### Quantum mechanics operators

should I solve it without the resolution of Identity?
16. ### Quantum mechanics operators

since the problems says for every state A so should I write as following ##<A_i|L|A_i>=0 \to ## then as before ## <B_j|L|A_i>=\sum_{i}<B_j|A_i><A_i|L|A_i>=0## is it right now?
17. ### Quantum mechanics operators

Homework Statement Suppose a linear operator L satisfies <A|L|A> = 0 for every state A. Show that then all matrix elements <B|L|A> = 0, and hence L = 0. Homework Equations ##<A|L|A>=L_{AA} and <B|L|A>=L_{BA}## The Attempt at a Solution It seems very straight forward and I don't know how...
18. ### Finding potential using Greens function

Homework Statement A potential ##\phi(\rho, \phi ,z)## satisfies ##\nabla^2 \phi=0## in the volume ##V={z\geqslant a}## with boundary condition ##\partial \phi / \partial n =F_{s}(\rho, \phi)## on the surface ##S={z=0}##. a) write the Neumann Green's function ##G_N (x,x')## within V in...
19. ### Can we make use of Greens function if there are no charges?

never mind I have found out where I was missing. your hint was very helpful. but there is one further question that pops out here. say we have written the greens function for such a problem in cylindrical coordinates, on the surface and considering the ##F_s = E_0## a constant, we arrive at the...
20. ### Can we make use of Greens function if there are no charges?

Lets say we have the following conditions given and we want to find the greens function in cylindrical coordinates: ## \nabla^2 \phi =0## this will eliminate the volume charge term in the equation for ##\phi## we also have that ##\phi|_{s} = F_{s}(\rho , \phi)## at the surface...
21. ### Can we make use of Greens function if there are no charges?

I can't think of a situation where we can utilize greens function without the presence of a point charge. lets consider the following equation: \Phi=\frac{1}{4\pi \epsilon} \int dv \rho(x')G_{N} (x,x')+ \frac{1}{4\pi} \int da F_{s}(\rho , \phi) G_{N} + <\phi>_S Here we see that a volume...
22. ### Partition function

first of all id like to thank you for taking time to answer my question. I have attached the 1st page of the original paper. well here we are dealing with lnZ since, later to find the average energy we have to take partial derivative of lnZ with respect to β.
23. ### Partition function

in the paper written by Jose Torres-Hernandez in 1984 titled as : "Photon mass and blackbody radiation" in the first page he writes for the partition function: lnZ=λ \sum_{normal modes} e^{-βε_l} = \frac{-λπ}{2} \int_{ε_0}^∞ n^2 ln(1-e^{-βε}) \frac{dn}{dε}dε i really don't understand...

It is indeed odd. But even more surprisingly i found what it refers to after reading the next chapter. After some pages it is indicated that the constant sigma actually refers to the damping constant (as the system is considered as damped oscillator since it emits radiation) but still i don't...

Thank you very much for your time. actually that is the part i didn't understand. because i don't see any relation between the formula for the conseravation of energy and σ , in the book it just appears suddenly and then the author concludes the final equation (the differential equation) by...

consider energy for a damped electric oscillator . ("f" indicates the dipole moment of the oscillator) in the absence of the damping force U= \frac{1}{2}kx^2 +1/2 (\frac{d^2x}{dt^2}) ^2 and the energy conservation tells us dU=0. but if there is damping force we get the following...
27. ### Relativistic Quantum Mechanics

@naturale and by the way naturale can you please show me the steps how you get that? we put the solution into ψ=Z(z)T(t) get the follwoing: ψ(z,t)=(Ae^{iωt} + Be^{-iωt})(Ce^{ikz} + De^{-ikz}) how do we apply the periodic conditions to this??
28. ### Relativistic Quantum Mechanics

@Fredrik well Im sorry I'm not really that good with -Latex- since i have just started using it. for the momentum Im just applying the following formula: π_μ = \frac{∂L}{∂(∂_μψ)} and applying this to lagrangian L=(1/2)[(∂ψ/∂t)^2 -(∂ψ/∂z)^2 -m^2ψ^2] we get the follwing : π_0 =...
29. ### Relativistic Quantum Mechanics

@Fredrik what I mean is that we have two partial derivatives (with respect to t,z) present in the Lagrangian so we have to apply the following formula: \frac{\partial L}{\partial ψ} = \sum_{i=1}^\infty \frac{\partial (\frac{\partial L}{\partial ψ_xi})}{\partial x_i} where x_i...
30. ### Research In Theoretical Physics

thank you very much tia89. I really appreciate your help. I think I will go for dark matter and dark energy since a lot of researches are being done in these fields recently.