Applies to questions of primarily educational value - not only questions that arise from actual homework assignments, but any question where it is preferable to guide the asker to the answer rather than giving it away outright. Please READ THE GUIDANCE IN META before asking homework-like questions.

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0
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1answer
15 views

Wave Equation - Vibrations & Waves

My question is basically how to do part ii) of this question even with the hint I am confused; the first part was simple; There's no dispersion & vp = vg = sqrt(hg) as required. But how would I ...
1
vote
1answer
28 views

How do you derive the Dirac equation for momentum space?

$\require{cancel}$ \begin{align} 0 &= i \gamma^\mu \partial_\mu \psi(x) - m \psi(x) \\ &= \int \frac{d^4 k}{(2\pi)^4}e^{-i k x}\left( \gamma^\mu k_m \tilde{\psi}(k) - m \tilde{\psi}(k) ...
0
votes
0answers
23 views

Gas Pressure in Industrial processes

Can anybody please help with the following? Ammonia is produced by the Haber process where nitrogen and hydrogen combine to form ammonia according to the equation: N2 + 3H2 == 2NH3 If 1 mole of N2 is ...
2
votes
1answer
35 views

What are the tidal effects of Io on Jupiter?

I recall reading an essay by Asimov (I think) around 1980 stating that the tides are a function of a power of the diameter of the primary, so (surprisingly) small close moons of Jupiter raise large ...
0
votes
1answer
39 views

Determine the equation of motion

The problem is the following. A ring of mass $m=1$ is moving along a circle of radius $R$ without friction. It's tied to a spring (coefficient $k$) of natural length $0$. The other end of the spring ...
1
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0answers
18 views

Hydrogen atom Ionization by Magnetic Field

The source of a magnetic field (it could be a magnetic dipole) is moving at relativistic speed. This magnetic field encounters a hydrogen atom at rest with respect to the source. Will this encounter ...
1
vote
1answer
43 views

Normalisation of a wavefunction

If the system if found in the state: $$\psi=\sqrt{\frac{1}{2\pi}}(\frac1{\sqrt3}e^{-i3\phi}+ce^{-i4\phi})$$ what value of $c$ normalizes the wavefunction? Clearly: $$\int_0^{2\pi}\psi^*\psi ...
1
vote
1answer
60 views

Radiation pressure (Jackson exercise)

Here's an exercise from Jackson: A plane wave is incident normally on a perfectly absorbing flat screen. From the law of conservation of linear momentum show that the pressure exerted from the ...
-1
votes
0answers
23 views

Balancing an equation [on hold]

I had an exam today and I havn't be able to find an answer to the question asking to balance this reaction equation, about oxalic and permanganate. Could you balance it or is it just impossible ? ...
-1
votes
0answers
36 views

Establish a relation between height of the water column and time in a $spherical$ container with a hole in the bottom

Suppose we have half of a sphere of radius $R$ filled with water. In the bottom of the container there is a hole of area $S_0$. Velocity of the water flow out of the hole is $$V=\lambda(2gh)^{1/2}.$$ ...
0
votes
1answer
29 views

Solving Lagrangian equations of motion for two point-bodies with gravitational interaction

I would like to solve the equations of motion with the Lagrangian function for two point-bodies that interact gravitationally via the potential $$V= {-Gm_1m_2 \over r_{12}} $$ where $$r_{12} = **r_1 ...
4
votes
2answers
45 views

Electric field due to a uniformly charged FINITE rectangular plate

I was teaching kids about how to find electric field using the superposition principle for continuous charge distributions, I thought may be I should derive the formula for electric field due to the ...
0
votes
1answer
49 views

Probability of finding particle in infinite square well, displaced walls

Initially a quantum particle moves in a one-dimensional well ($x$-axis) from $-a$ to $ a$, $ V = \infty $ outside and $ V = 0 $ inside the well. So initially, the wave-function $$ \psi_0 = ...
0
votes
1answer
29 views

System of two harmonic oscillators and its quantum partition function

Consider a system of two harmonic oscillators with different frequencies $\omega_1,\omega_2$ and masses $m_1,m_2$ so the hamiltonian is $$\mathcal{H}(p_1,q_1;p_2,q_2)=\sum_{i=1}^2 ...
2
votes
1answer
59 views

Can someone explain this solution for the motion of a falling chain?

In an example of Marion's classical dynamics 5th edition, I found example 9.2 not making sense, which states: My questions are: The horizontal motion cannot be ignored even in the idealized ...
0
votes
0answers
19 views

How to calculate free energy mixing of a solution?

http://imgur.com/tCBG7kF I'm struggling with part d). Given the volume fraction for oil as 0.3, I've assumed to use the other volume fraction as 0.7 to follow with the incompressibility condition as ...
0
votes
1answer
36 views

Showing existence of negative temperature for a quantum system

It may be shown that the partition function for a quantum system containing N distinguishable particles each of which has energy state $\epsilon_1$ and $\epsilon_2$ is given by ...
0
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0answers
31 views

Quantum Mechanics for 1D box

For particle in a box with mass $M$ length $L$,assume $\Delta x=L$. Assume further that $\Delta p_{min}=\langle p^2\rangle^{1/2}$.Use the uncertainty principle to obtain an estimate of the energy of ...
0
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0answers
20 views

A linear response system with a periodic input

I'm currently trying to solve the following exercise: A linear system is driven by a periodic input $f(t)$ such that $f(t+T)=f(t)$. The response $g(t)$ of the system is such that a sinusoidal ...
0
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0answers
20 views
-1
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0answers
31 views

Kepler law - 2 proof (area vectors) [on hold]

How to prove Keplers second law? I tried but I could not get how to make the proof in area vectors and time Differentiated equation can't be used for area vectors then how to prove it?
1
vote
0answers
30 views

Killing vector field along geodesic [on hold]

I was trying to show that a Killing vector field satisfies the Jacobi Equation for a geodesic, just by assuming that \begin{equation} \nabla_\mu X_\nu + \nabla_\nu X_\mu=0 \end{equation} Indeed, if I ...
1
vote
2answers
36 views

Period of a simple pendulum accounting for friction

The period of a simple pendulum is $$T=2\pi\sqrt{\ell/g},$$ but no where in there do I see that it accounts for friction. Does it somehow account for friction, and if not, how could you do that?
0
votes
2answers
81 views

Calculating quantum partition functions

...By quantizing we the get the following Hamiltonian operator $$\hat{H}=\sum_{\mathbf{k}}\hbar \omega(\mathbf{k})\left(\hat{n}(\mathbf{k})+\frac{1}{2} \right)$$ where ...
0
votes
0answers
18 views

Photon sphere of Sagrittarius A* , calculation correct? [on hold]

For Kerr Parameter a=0.52, my result for the photon sphere of Sagrittarius A* is ca. 19 Mio. km. (direct orbit and retrograd) Equation Calculation (direct orbit) I am not sure about the arccos ...
-2
votes
0answers
36 views

Please help in this question [on hold]

An object slides down frictionlessly from the top of a fixed straight slope of base 30cm.At least how long does it take for the object to slide down?
0
votes
1answer
31 views

What are the state variables like temperature after the system has done an adiabatic irreversible process? [on hold]

Consider a system containing ideal gas which is initially at a volume $V_{1}$ and then suddenly its volume is increased to a volume $V_{2}$. What is the final temperature of the system if the initial ...
0
votes
0answers
24 views

Mass of lead balls (Cavendish experiment) [on hold]

I have to find the mass of those two lead balls, what is given is the following things: Radius ball 1 [meters] $$0.05$$ Radius ball 2 [meters] $$0.3$$ And the next formulas: where G is the ...
2
votes
1answer
48 views

How do you prove that $L=I-V+1$ in $\lambda\phi^4$ theory?

It is known that the number of loops in $\lambda\phi^4$ theory is given by the formula $$L=I-V+1$$ where $L$ is the number of loops, $I$ the number of internal lines and $V$ the number of vertices. ...
0
votes
0answers
19 views

How do you find current in this electromagnetic induction problem? [on hold]

I'm a bit lost on this. I'm given bfield strength, a velocity, and a length, and also resistance. However, I have no idea how to use any of those variables to find a current.
1
vote
0answers
14 views

help calculate the Rydberg constant for hydrogen [on hold]

The wavelength difference between the longest lines in the Balmer and Lyman series for hydrogen is 534.7mm. Calculate the Rydberg constant for hydrogen.
-1
votes
0answers
54 views

amplitude of two carts attached by a spring [on hold]

The problem statement: All variables and given/known data [Coupled Oscillators] A cart of mass $m$ (car #1) and another cart of mass $2m$ (car #2) on a horizontal surface are connected by an ideal ...
0
votes
1answer
33 views

Concerning railguns and magnetic fields

I'm part of a group working on a Physics II project based on electromagnetism, and my group decided to create a proof-of-concept railgun, shown here: ...
0
votes
0answers
31 views

Finding final velocities given initial velocities and angles [on hold]

You and a friend stand on a snow-covered roof. You both throw snowballs from an elevation of 14 m with the same initial speed of 12 m/s, but in different directions. You throw your snowball downward, ...
0
votes
0answers
15 views

Rheostat and how ohms affect them [on hold]

I have a two welding machines with the same problem. The rheostats, Ohmite 1.5Ω, 5.77 amps, are damaged. The replacement cost from manufacturer are $100 each. After searching on ebay I found some ...
0
votes
0answers
26 views

Friction forces [on hold]

I have a cylinder filled with water with mass $M$ rotating on the axle with angular velocity equal $\omega$ Friction loss is about $2\%$ How friction loss (in percentage) will be changed if speed ...
1
vote
0answers
17 views

Displacement Vectors [on hold]

Displacement vectors of 3m and 5m in the same direction combine to make a displacement vector. How long is it? What is a displacement vector and how do I calculate this?
1
vote
0answers
24 views

Diffusion of a chemical proof (fick's law general)

I want to prove that: $$C(x,t)= \frac{C_0}{\sqrt{4\pi Dt}} \exp\left[{\frac{-x^{2}}{4Dt}}\right]$$ I've proven so far that Fick's law coupled with the conservation of mass (assuming no influx or ...
0
votes
0answers
12 views

Absortion of light by a plasma

Considering a plasma generated in a fixed volume by increasing the temperature of Helium gas from the environment temperature (this temperature is not stated) and an initial presure of 0.001 Torr, to ...
0
votes
0answers
13 views

How to find heat transfer and released heat? [on hold]

Given the sterling cycle with the following processes 1-2 isothermal expansion - heat addition from external source 2-3 constant volume heat transfer - internal heat transfer from the gas to the ...
3
votes
0answers
28 views

Transformation law for field strength tensor [on hold]

How do I derive the transformation law for the field strength tensor$$F_{\mu\nu}^A = \partial_\mu V_\nu^A - \partial_\nu V_\mu^A - gC_{BC}^A V_\mu^B V_\nu^C$$to show that it transforms like a vector ...
-2
votes
0answers
13 views

Finding the temperature needed to have speed of gas atom equal to Ve [on hold]

We are given n moles of a monatomic gas Argon Molar mass 6.4*10^-26. Pressure equal to 101300 pascals. Temperature = 300 K Need to find the average speed of one of the atom of the gas. Secondly I ...
0
votes
1answer
29 views

Normalisation of simple wave function [on hold]

I'm currently hanging on a simple normalization of following wave function: $$\psi_1(x)=N_1\exp(-\frac{(x-a)^2}{4a^2}),$$ where $N_1$ is the normalization factor to get, and $a\in \mathbb{R}$ ...
2
votes
1answer
63 views

White noise and Fourier transform

I try to solve a Langevin equation in the Fourier space. My understanding of the white noise in the Fourier space seems to be wrong. Suppose I have a particle with its time evolution of the position ...
1
vote
1answer
40 views

To find average speed of gas molecule when the temperature is incresed

We are given moles of gas let say $n$. Temperature is increased from $T_1$ to $T_2$. Volume is held constant at $V_0$. We need to find the average speed of gas molecule when the temperature $T_2$ is ...
-3
votes
1answer
29 views

Using creation and annihilation operators to prove the expression for the $n$th excited state in terms of the vacuum state

How does one prove that the $n^{th}$ excited state of a quantum harmonic oscillator (QHO) can be obtained by applying the creation operator $a^{\dagger}$ $n$-times to the vacuum state $\vert ...
1
vote
1answer
41 views

Derivation of Interaction energy of Dipole - Induced Dipole Interaction

I see that the formula giving the potential (interaction) energy of a dipole and an induced dipole is $$V=-\frac{C}{r^6}$$ where $$C=\frac{\mu_1^2 \alpha'_2}{4 \pi \epsilon_0}$$ and that the formula ...
0
votes
1answer
23 views

How to calculate the radiation impedance of the horn loudspeaker?

The mouth of the horn is circular and there are many models in order to approximate the radiation impedance, such as: massless circular piston in an infinite baffle, unbaffled massless ...
-3
votes
0answers
52 views

Jee mains 2015 online [on hold]

A particle is moving in circle of radius r under the action of force F=ar^2, which is directed towards centre of the circle. total mechanical energy (kinetic + potential) energy of the particle (take ...
1
vote
1answer
21 views

showing that polytropic exponent n = 5/3 corresponds to an isentropic process for a monoatomic ideal gas [on hold]

Given an ideal monoatomic gas with $pV = NT$ and $E = \frac{3}{2}NT$ what are the types of processes described by $n = 0, 1, \frac{5}{3}$, where n is the polytropic exponent ($p V ^ n = const.$)? ...