# All Questions

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### An image in movement viewed by different cameras [on hold]

Why in the image the string looks like is in two places at the same time, what is the optical reason or is it because of how cameras work?
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### Combining sound absorption coefficients

I am trying to predict the reverberation time in a room with different surfaces and different absorption coefficients (i.e. curtains, wood panels, carpet etc). My question is about how to calculate ...
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### D branes Ns brane and p-branes

It is now a common knowledge that "D-p branes are equivalent to p-branes" due to Polchinski's work. Note that D-p branes are objects in string theory and p-branes are objects in blackhole theory. So ...
24 views

### How to parametrize off-shellness?

The energy of a massive on-shell particle of mass $m$ and three-momentum $\vec{p}$ satisfies $$E_\vec{p} = \sqrt{\vec{p}^2+m^2}.$$ What would be the analogous expression for an off-shell particle? ...
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### Calculation of angular acceleration [on hold]

Hi I am doing a physics question and it's like this: Two identical blocks, each of mass M, are connected by a massless string over a pulley of radius R and rotational inertia I . When the system is ...
41 views

### Why 5D gauge theory is non-renormalizable?

My question is following "Why 5D gauge theory is non-renormalizable?" Here I treat $5D$ supersymmetric gauge theories. Also I heard Non-renormalizablity of $5D$ gauge theories implies the ...
44 views

### Thermodynamics : Work done on gas inside container by the force due to pressure exerted by external atmosphere

Suppose a container is fitted with a massless and frictionless piston lying on a table such that pressure due to gas is greater than pressure due to external atmosphere. Hence piston will move. Now ...
18 views

### Calculating the entropy of a monatomic ideal gas

I am looking at the start of the consider how to calculate the entropy of a monatomic ideal gas. We need to determine the number of microstates in $E \leq \mathcal{H}(\Gamma) \leq E+\Delta$. The ...
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### Perceived solution to grand unification theories and more specifically the TOE [on hold]

My question is doesn't the fact that escaping Earth's atmosphere significantly reduces gravitational attraction lead one to agree with Einstein's original intuition that aether is everywhere and ...
292 views

### Reflected and refracted light have same frequency as that of the incident light frequency. Why?

My text book says- When a monochromatic light is incident on a surface separating two media, the refracted and reflected light both have the same frequency as the incident frequency. Can anyone ...
24 views

### Why don't we consider cubic terms in the Higgs potential? [duplicate]

In the Standard Model scalar potential, we only consider quadratic and quartic terms, why not cubic terms though? I've noticed also in BSM theories with one extra scalar singlet, only quadratic and ...
19 views

### In the Standard Model Lagrangian, why does every term's mass dimension have to be less than four?

In the Standard Model Lagrangian, why does every term's mass dimension have to be less than four? I know that the Lagrangian has to be renormalizable, I guess my question then translates into why ...
50 views

### How do you visualize a quantized electromagnetic field?

Quantizing the EM field gives you the standard sum of all quantum harmonic oscillators as given by this hamiltonian: $$\hat{H} = \sum_k \hbar\omega_k( \hat{a}^\dagger_k \hat{a}_k + 1/2)$$ ...
32 views

### Bounce height of ball on Mars vs Earth

I understand that if a ball is dropped on mars and on earth the ball will bounce back to basically the same height on both planets thanks to the law of conservation of energy. But can anyone prove ...
29 views

### Why does negative energy imply that a system is bounded? [duplicate]

I wanted to know why "negative energy" of a two particle system implies that it is bounded. That is what happens in the case of a hydrogen atom; my textbooks say so, but they do not give any reason ...
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### The standard textbook on supernovae?

This is a straightforward question: What is considered to be the standard treatment of supernovae? Could be a textbook, lecture notes, review article, etc.
15 views

### Numerical Estimates for the fermi Energy [on hold]

The question is to give the numerical estimates for the Fermi Energy of electrons in a typical metal, nucleons in a heavy nucleus and $He^3$ atoms in a liquid $He^3$ and compare the results. I know ...
52 views

### What is meant by a “sodium line”?

What speed should a galaxy move with respect to us so that the sodium line at $589.0\ \mathrm{nm}$ is observed at $589.6\ \mathrm{nm}$? In the above question what's meant by a sodium line? The ...
22 views

### Conformal group and stereographic projection

In Ginsparg's Applied Conformal Field Theory (http://arxiv.org/abs/hep-th/9108028, on the bottom of p. 5) the following remark is made: Indeed the conformal group admits a nice realization acting ...
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### As an older student, is it better to finish my degree or go straight into studying physics now? [on hold]

I'm a 23 year old going through a very early mid-life crisis, and considering a career change to physics. I would be very greatful for any advice :) I'm currently studying medicine, but I've realized ...
24 views

### Acceleration of an incompressible fluid along a conical pipe [on hold]

I've been reading Theory of Flight by Richard von Mises and early on I came across this problem. The full text of the problem is as follows: "Show that along a conical pipe the acceleration of an ...
42 views

### Scientific Laws for Engineering Materials [on hold]

I have a conceptual question. There is a law in science for every phenomenon in nature, like gravity or electric field. But also there are laws for springs or capacitors etc... I mean the ...
28 views

### Pendulum point in polar coordinates for Lagrangian

So I'm really stumped with this. I have a particle in a cone, like pictured. The particle orbits the z axis on the dotted line for $r$. So knowing that $\alpha$ and $r$ remain constant in this ...
19 views

### Spectroscopy - Absorption lines

Let's say we run a light source (a strong torch) with full spectrum light through a big, transparent, glass box filled with neon. Will we be able to see any Fraunhofer lines on the spectral analysis ...