# All Questions

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### Measuring the solid air surface tension

For hydrophilic and hydrophobic materials, $Y_{SG}$= Interfacial tension between the solid and gas $Y_{SL}$ = Interfacial tension between the solid and liquid $Y_{LG}$ = Interfacial tension ...
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96 views

### Finding Tension in an Elastic String?

I know that this is a homework type question and I'm not asking a particular physics question, but I'm really desperate for help. Here's the question: I tried to divide the string to 2 parts with ...
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56 views

### Condensate fraction and single-particle density matrix

In Bose–Einstein condensation (BEC), how to prove the largest eigenvalue of the single-particle density matrix $$\rho_{ij}=\frac{\langle\Psi|a_i^{\dagger}a_j|\Psi\rangle}{N}$$ is ...
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72 views

### path integral quantization of EM field derived from canonical quantization?

In Peskin's QFT book page 294, he formally addressed the quantization of EM field, $$propagotor_{EM}=\frac{-ig_{\mu\nu}}{k^2+i\epsilon}$$ Now that we have the functional integral quantization ...
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386 views

### Hysteresis Curve and how to implement it using Preisach model or other models

As a homework I need to draw a hysteresis curve (preferably an interactive one) using Matlab or any other programming language. The problem is I have trouble finding a good algorithm to do so. I need ...
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60 views

### Beamsplitter and Dielectric Mirror

Among two optical components. One is a Nd:YAG Laser 50/50 Beamsplitter and the second one is a Dielectric Mirror see pictures. Both of them almost looks like the same. If the specification is not ...
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112 views

### Were Maxwell's equations first formulated by McCullough?

Some years ago, I heard a talk about a an Irish or Scottish physicist named McCullough who had formulated Maxwell's equations several years before Maxwell. This fellow was recognized for his work, ...
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39 views

### Could a strong AC electric field adversely affect the capacity of a lithium battery?

I run some battery powered test equipment in close proximity (~10cm) to a conductor carrying 25kV (50Hz AC). I find the battery life is much shorter than expected, having checked the current ...
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### Compact manifold taken as an Einstein Manifold

In Kaluza-Klein theories I often see that the compact space is assumed to be an Einstein manifold, that is, its Ricci tensor is proportional to its metric. So, why is this done?
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### If air was significantly compressed, and then the force compressing it suddenly disappeared (no container), what would happen?

Question: If air was significantly compressed, and then the force compressing it suddenly disappeared (no container), what would happen? Side Question: I'm imagining significantly compressed, but ...
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68 views

### Conformal mapping for calculating magnetic reluctance

I work currently on the calculation of magnetic resistance for a air-gap of an electrical machine. For this I am using conformal transformations. I am doing this on a 2D slice. As the machine is ...
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189 views

### Uncoupling a coupled oscillator Hamiltonian by change of variables

I'm working on the problem of two entangled harmonic oscillators with Hamiltonian: $$H = \frac{1}{2} [p_1^2 + p_2^2 + k_0(x_1^2 + x_2^2) + k_1(x_1 - x_2)^2].$$ Introducing the variables \$x_± = ...
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### Which power should a radio transmitter have to overcome attenuation of 100 km thick ice crust?

Imagine I put a floating probe inside the subglacial ocean of Encelado or Europa: how much power should my radio have to be able to communicate from external surface with the probe? Or, in different ...
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35 views

### What can I say about compatibility between predictions and results?

If I have these theoretical predictions: \begin{align} \omega_{p_1} = 4.5132 \pm 0.0003~\text{rad/s} && \omega_{p_2} = 4.5145 \pm 0.0002~\text{rad/s}\\ \omega_{b_1} = 0.0707 \pm ...
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I'm looking at the radiosity equations for heat transfer http://en.wikipedia.org/wiki/Radiosity_(heat_transfer)#Radiosity_method Specifically, I'm hesitant to accept the equation: \dot Q_i = ... 0answers 38 views ### Regulating a particular function I am interested in computing the integral of this function: \begin{align} \int_0^\infty\frac{2du(u^2+1)}{(1-e^{2\pi u})}, \end{align} which of course at first sight, does not converge. But in QFT ... 0answers 22 views ### Instabilities in the CDMT Could anyone explain or refer to references on why the CDMT f(R) gravity model suffers from Instabilities any why the sign of {\mu}^{4} matters. 0answers 103 views ### Restrained double pendulum The equations of motion of a double pendulum are well-known. Usually you'd have the them expressed in the rotations \theta_1(t) and \theta_2(t). There are two degrees of freedom. Now consider the ... 0answers 26 views ### Time scale when measuring total activity from radioactive sample I have measured the total activity from a radioactive sample during an experiment by counting the number of decays happening in 3 seconds intervals. I got data as: Time bin: 0 1 2 3 4 5 6 7 ... ... 0answers 139 views ### Finding Time & Required Angle for Projectile Motion with Quadratic Air Resistance This is a physics/calculus/computer science problem, but I think I'll get better results in the Physics SE. I have a fun little project I've been working on (hobby, not homework/production), that ... 0answers 116 views ### Physical Meaning of Linear dependence of vectors in quantum mechanics I have got some questions regarding the mathematical concepts in Quantum Mechanics that I have listed below- 1) What is the physical meaning of linear dependence of vectors in Quantum Mechanics ? 2) ... 0answers 32 views ### Quantity with approximate lognormal distribution I am studying a quantity x for which \log( x) is nearly (although not exactly) lognormal. What would be the appropriate "typical" value: the mean \langle x\rangle or rather ... 0answers 59 views ### Ion-neutralization processes and its energies Ionization energies/Electron affinities are well mapped. I wonder about opposite processes... I imagine for anion the necessary energy will be equal to the electron affinity (energy released when ... 0answers 53 views ### Stationary wave on a string The problem says: A string lies on the x-axis, and is fixed at  x=-a  and  x=a . At  t=0  we impose a transversal velocity given by  a^2-x^2 . Assuming that the velocity of the wave is  c ... 0answers 410 views ### Sommerfeld radiation conditions for an electromagnetic field There is some confusion in the definition of Sommerfeld radiation conditions for an electromagnetic field, which are related to the asymptotic behaviour of the field for a distance r \to \infty ... 0answers 29 views ### Multiple Entanglement What happens when certain percentage in a group of multiple photons with same quantum state change their state. Does it affect all photons in the group or some members? 0answers 300 views ### Can somebody explain the graphical integration method in a better way? After hours of research all what I can find is this: http://www.public.iastate.edu/~fanous/ce332/virtualwork/homepage.html can somebody explain this method in a better way. If the moment diagram ... 0answers 122 views ### Can I detect/measure strength of a FM radio wave using a Electro magnetic field meter? I understand that an alternating current produces an Electro magnetic field . The strength of this magnetic field can be measured by measuring devices. What I wanted to understand is Are the FM ... 0answers 49 views ### What will be the direction of the force required on the ball to move the ball up the stairs? Is this diagram correct? The point of force A is at the farthest distance from the fixed centre O ,so the moment arm CD is greater and therefore,maximum torque would be produced.Is my concept ... 0answers 128 views ### Symmetry argument about degeneracy of graphene energy band at Dirac point This question is very related to the thread here. In the answer given by @BebopButUnsteady , the statement is that as long as the inversion and time-reversal symmetry are respected, the Dirac points ... 0answers 131 views ### Number of wave modes in a cavity I'm trying to calculate the number of acoustic modes that can exist in a room in a certain range of frequencies. I thought of using the Rayleigh-Jeans formula for the electromagnetic standing wave ... 0answers 49 views ### Four-current, Induced Charge and Magnetic Flux I'm studying Jackiw's "Fractional Charge and Zero Modes for Planar Systems in a Magnetic Field" DOI: 10.1103/PhysRevD.33.2500 but I have difficulties at some points. One of the problems is\langle ...

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