All Questions

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1answer
108 views

Why does a green glass block more UVA/B rays than a blue one?

Why does a green glass block more UVA/B rays than a blue one? White glass blocks 36%, blu 43% and green glass blocks most UVA rays. That is why beer and olive oil bottles are green, they say. Edit: ...
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1answer
51 views

Photons “rate of fire”

I'm not sure if this makes any sense but, do photons "discharge" from a source at an infinite rate?
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2answers
259 views

Force Diagram for K&K 2.13 [closed]

I have been (independently) working on Problem 2.13 in Kleppner and Kolenkow's An Introduction to Mechanics and come to an answer which conflicts with the hint the authors provided in the book. The ...
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1answer
28 views

Electric Potential of Conductors

I understand that charges in a conductor reside on the surface of a conductor. So why is it that the neutral inside of a conductor and the charged surface are at the same potential?
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1answer
56 views

geodesic conjugate points

I was reading "Nature of space and time" by Penrose and Hawking, pg.13, If $\rho=\rho_0$ at $\nu=\nu_0$, then the RNP equation $\frac{d\rho}{d\nu} = \rho^2 + \sigma^{ij}\sigma_{ij} + ...
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1answer
140 views

Thermodynamics for Dummies: Entropy and temperature

I do not study physics and I have never had a course in thermodynamics. I have no idea what it is about, but I am currently taking a course where we had something about entropy. Would be great if ...
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2answers
64 views

Would an object lose physical mass if it accelerated to a relativistic speed (would an object burn it's own mass)?

First of all, I have read other questions, and seen how an object gains mass just by gaining a lot of speed. But here, I am talking about losing some of that mass to convert the value into kinetic ...
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1answer
58 views

What is the physical basis of the $\rho \bf{u} \times \bf{\omega}$ force on a fluid vortex line?

In fluid dynamics, the force density on a vortex line is $\bf{f} = \rho \bf{u} \times \bf{\omega}$. In Faber, Fluid Dynamics for Physicists, ch. 4, this is "derived" by analogy with magnetostatics, ...
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1answer
49 views

Action Reaction Pairs and Work

Say that a ball is sitting in front of a compressed spring launcher. The spring is then released. The spring applies a force on the ball for a certain distance. This force is accompanied by an equal ...
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1answer
112 views

Doubt in a certain equation of a research paper [closed]

In the given paper, I am stuck at equation (7). The equation that I am trying to solve for particle outside the well is : (1/g)*(g'') + (1/(r*g))*g' - (k_o)^2 = 0 where g = Radial wave function. r = ...
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1answer
43 views

Density of Solid States of Compounds

One of the wonderful properties of water (as my high school biology teacher would say) is that in its solid form, it is lighter than its liquid form. This means that when temperatures drop below 0 ...
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1answer
63 views

Hugh Everett's MWI [closed]

According to Hugh Everett's many worlds interpretation, all the possibilities of one action can happen at the same time in other parallel universes, so how come we can't see these worlds? now I bumped ...
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2answers
82 views

amplification of magnetic field

can we by any means amplify magnetic signal as we can with electric signal. As both electric and magnetic field can be represented in the form of a wave the analogy seems to be natural. I want the ...
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3answers
57 views

What is spin on a lattice site is it electrons or atom as a whole?

Hi I wanted to know what is spin half in lattice site means? Is it electron or atom or total spins half of electrons in a atomic 1d chain or 2d?
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3answers
84 views

How damaging is light? [closed]

On Surely You're Joking Mr Feynman, when talking about the Trinity test, the author states: the only thing that could really hurt your eyes (bright light can never hurt your eyes) is ultraviolet ...
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1answer
77 views

Instantons as a -1 dimensional object

I don't know much about Instantons, and looking through the Wiki page it seems like one must have a lot of knowledge about QFT to understand them. However recently I've encountered a statement (which ...
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1answer
63 views

Hooke's Law: why is only one force considered?

I have a question about Hooke's Law springs. What I learned is that a Hooke's Law spring gives a force F pushing left and right and each force equals $k \cdot |l-l_o|$ Let's say there is a mass ...
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1answer
66 views

Calculating the magnetic field due to a rotating ring using Biot–Savart law

I wish to calculate the magnetic field due to a charged ring rotating about an axis perpendicular to the plane of the ring and passing through a point on its circumference $(P)$. I arrive at something ...
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2answers
55 views

Does the mass distribution matter in (Schwarzschild) black holes?

Is it possible that from the same initial mass different black hole radius will be created due to different mass distribution during black hole creation? If mass is concentrated more on the outside ...
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1answer
76 views

Will A Vertical Projectile Travel the Same Distance as A Horizontal Projectile

If a projectile is fired vertically from an initial height, $h$, above ground level, and an identical projectile is fired with equal initial velocity from the same initial height in the horizontal ...
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1answer
66 views

What are the similarities and differences between speech and music sounds?

From an acoustic perspective, I guess speech sounds are produced by varying/manipulating: resonance (shaping the cavity; something to do with harmony?) f0 (the length of the string/pipe/whatever) ...
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1answer
42 views

What is the status of massless photons traveling through a medium?

Photons in vacuum have no proper time, and they are not considered as observers and not as reference frame. But what about photons travelling through matter? Their velocity is lower than light speed, ...
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1answer
83 views

How can I actually push heavier objects?

I've been thinking about Newton's third law lately because I couldn't understand a few things and I think I actually answered my own question. Could someone confirm if my reasoning is right or show me ...
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3answers
120 views

Why does $\nabla \to ik$ when you Fourier transform?

I am reading a text that describes the scattering of light by a particle with dielectric constant $\epsilon$ After a bit of maths starting from Maxwell's equations they obtain: $$\nabla (\nabla ...
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2answers
61 views

Toy models of asymptotic safety?

Are there some toy model QFTs where the asymptotic safety scenario is realized?
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1answer
46 views

Magnet substitution [closed]

I wonder if the two magnet configurations below are equivalent. If they are not - what will be the effects on the flux?
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1answer
39 views

Coordinates of the extra dimensions

If we live in more than three spatial dimensions, is it not right to conclude that all matter observable to us shares almost the same coordinates of extra dimensions. Or is it just that ordinary ...
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1answer
68 views

A question about the asymptotic series in perturbative expansion in QFT

Related post I heard about the argument that the perturbative expansion in QFT must be asymptotic, such as http://ncatlab.org/nlab/show/perturbation+theory#DivergenceConvergence Roughly this can ...
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1answer
114 views

Lagrangian and grassmann numbers

Why sometimes we remember that "classical" lagrangians of fermions are constructed from grassmann numbers, while sometimes don't? For example, for Majorana's field in terms of 2-component spinors ...
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2answers
58 views

Applying a force on a rigid body which is used to create torque

In the above picture, I have a rigid body, in turquoise, which is connected to a point, the red circle. The dotted lines are used to divide objects or lengths, they are not part of the rigid body. ...
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2answers
145 views

Relations between pressure and temperature

I have several questions concerning thermodynamics and I order them in 4 points that may be related: What's the difference between heat and work at the atomic level? Isn't heat simply work between ...
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2answers
217 views

Unit of gradient/slope?

So I have a graph: The value of the gradient/slope is $1.6±0.4$ and the value of the intercept is $0.9±0.4$. But what are the units of the graph? Is the unit of the gradient $v^2M^{-1}$? What about ...
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1answer
87 views

My orbiting body is orbiting about the wrong focus of it's elliptical orbit… why?

I am coding in c++ and am computing the position of an orbiting body as a function of time. Everything is almost working. I have a nice elliptical orbit. Except, my orbiting body speeds up as it ...
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2answers
84 views

Experimental Verification of No Special Frames of Reference

Certainly, there have been numerous tests of both Special Relativity and General Relativity. Given all the phenomena and behavior stipulated by Relativity, one could perhaps divide these phenomena ...
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1answer
58 views

Weak interaction violate charge conjugate

How can we show that the weak interaction violates the charge conjugation symmetry?
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1answer
56 views

Redshift of a reflected photon from a solar sail

Can someone help me understand my mistake here? I'm thinking of a photon travelling with momentum $p=h/\lambda$ which reflects off a solar sail of mass $m$ travelling with momentum $p_0$ in the same ...
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3answers
48 views

How to approximate acceleration from a trajectory's coordinates?

If I only know $x$- and $y$- coordinates of every point on a trajectory without knowledge of time information, is there any way to approximate Cartesian acceleration angle at each point? Time interval ...
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1answer
61 views

Are antiparticles just particle-shaped holes?

If particles are simply regions of space where certain quantum fields have non-zero divergence, are anti-particles simply the corresponding regions of opposite divergence? This seems like the ...
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1answer
82 views

Has anyone yet been able to prove relativity wrong? [closed]

I was in a physics group, then a student (or a professor, I don't know) posted this- Mohammad Shafiq Khan > Physics > The space-time concept including the formula $E=mc^2$ are proved baseless in ...
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1answer
180 views

Why does magnetic field increase when the number of coil turns increase?

Since we all know that to increase the magnetic field we can do these of the following things: (i) Increase the number of turns in a coil, (ii) Increase the current following through conductor, and ...
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1answer
51 views

Is there a standard resource that lists all understood particle-particle relationships?

I am just starting to dig a little deeper into particle interactions, and just have an introductory college physics background (no quantum mechanics). But I am interested in the conditions of the ...
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2answers
87 views

Why do liquids boil when their vapor pressure equals the ambient pressure?

Given that the boiling point of a liquid is the temperature at which the vapor pressure is equal to the ambient (surrounding) pressure, what significance does a liquid's vapor pressure have in the ...
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1answer
77 views

In which loop does the induced emf remain constant during the passage out of the magnetic field region?

A rectangular loop and a circular loop are moving out of a uniform magnetic field to a field-free region with a constant velocity V as shown in the figure. Explain in which loop do you expect the ...
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1answer
90 views

Perturbation theory emitting high order powers

For my second-order energy correction for a harmonic oscillator in an electric field I have the following: $$q^2\varepsilon^2\sum_{m\neq n}\frac{|\langle m|x|n\rangle|^2}{E^{(0)}_n-E^{(0)}_m}+\text{ ...
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3answers
144 views

How much of the sky is visible from a particular location?

From a particular point how much of the sky can be observed. For simplicity sake let us assume the particular point is the head of a 6 foot tall man floating in the middle of the ocean with no visible ...
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1answer
62 views

Time homogeneous Markov chain for Axelrod's model

I am reading paper Axelrod's model of dissemination of culture , I am unable to understand the transition probabilities of time homogeneous Markov chain for this model. Can some one please explain it ...
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1answer
79 views

Interpretations of (r,s) tensors [duplicate]

A tensor of type (r,s) on a vector space V is a C-valued function T on V×V×...×V×W×W×...×W (there are r V's and s W's in which W is dual space of V) which is linear in each argument. We take (0, 0) ...
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2answers
69 views

Where does wave frequency come from

I am trying to wrap my head around where do oscillations in electromagnetic waves come from. As an example if I would take a string of guitar and ring it, it would produce a certain sound based on the ...
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1answer
37 views

$m_l=0$ in Hydrogen atom of Scrodinger equation

$m_l=0$ corresponds to s-orbital and the values associated are: $$\lambda=2\pi r/m_l\to\infty$$ It means a wave of of infinite wavelength has a constant height at all values of $\phi$(azimuthal ...
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1answer
39 views

Entangled Electrons

What attribute would help determine in a spaghetti of tangled-entangled electrons, which two are the respective entangled electron pairs, since obviously there is an attribute other than charge or ...

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