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1answer
49 views

Is there a heuristic argument for the expression $ \textbf{g} = \frac {\mathbf{S}}{c^2}$?

Electromagnetic momentum density and the Poynting vector are related by the simple expression: $$ \textbf{g} = \frac {\mathbf{S}}{c^2}$$ It can be rigorously derived from Maxwell's equations, but is ...
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3answers
109 views

Can the vacuum be filled with virtual micro-black holes?

Since the vacuum is thought to be virtual particles, is it possible that there might be virtual micro-black holes with virtual horizons and virtual hawking radiation which form and evaporate at a rate ...
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1answer
163 views

Paper in physics - calculations; rounding or not?

I'm currently a high schooler, and I'm writing my first scientific paper. The result is fairly simple, and it is nothing too special, but I see it as a nice way to prepare myself for the academic ...
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2answers
419 views

$\gamma$ in Newton's Second Law of Motion in Differential Form

I am teaching myself Differential Equations from a website. In the website I am up to Direction Fields and an example of a differential equation is Newton's Second Law of Motion. It is written on the ...
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2answers
151 views

Light in fibre optic cables

Imagine a fibre optic cable stretching from London to New York (5571 km) carrying a data signal This data signal is split into two parts, red and blue light Both signals start travelling down the ...
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1answer
2k views

Are the perpetual machines in this video really perpetual?

This video lists a number of perpetual motion machines that have been proposed throughout history: Robert Boyle's Self-Flowing Flask A "perpetual train" using rolling cones F. G. Woodward's hoop ...
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1answer
436 views

Why the electric force does no work on the charge when perpendicular to the field?

I was reading my physics textbook and came across this sentence: When a charge moves in an electric field, unless its displacement is always perpendicular to the field, the electric force does ...
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1answer
131 views

Chemistry from a physical perspective [duplicate]

I'm currently learning chemistry for the first time, and loving it. I have a reasonably good physics and maths background and it's great to see things like spherical harmonics in quantum mechanics ...
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1answer
124 views

Wavefunction's inner product

When two wavefunctions are orthogonal we can write that $$\langle\Psi_n|\Psi_m\rangle=\delta_{mn}$$ This means that $$\langle\Psi_1|\Psi_2\rangle=\langle\Psi_2|\Psi_1\rangle=0$$ But if the two ...
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1answer
92 views

Motion in insulating fluid under high voltage

I observed the following phenomenon in an experiment (I'm not a student of physics, just an amateur) and was hoping for an explanation. A metal pan is electrically grounded and a layer of insulating ...
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2answers
213 views

Frames of reference: Inertial and accelerated - and jerked, snapped, crackled and popped?

There are inertial frames of reference and the accelerated frames of reference, but are there any frames of references w.r.t. higher order derivatives of velocity? [1] [2] For example, jerked frames ...
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2answers
373 views

Wave function decomposition

Problem: Given the wave function $\Psi_0=A\sin^2(\theta)$ along with the Hamiltonian operator of a physical system: $H=\frac{L^2}{2I}+g B L_z$, find the eigenvalues and eigenfunctions of $\hat{H}$ ...
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1answer
126 views

determining orbit parameters (eccentricity, length and angle of major axis)

I'm trying to make an orbit simulator, and I want to draw the orbit of a satellite given its position and velocity vectors in a 2-D plane. I found this other question which tells how to calculate ...
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1answer
116 views

Why linear wave equation does not have solitonic solutions?

As many people define solitary waves they are localized pulses that propagate without changing the shape. As far as I know the same pulses exist in ordinary wave equation ! why should we look for ...
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1answer
131 views

Does the Sun orbit a much larger nearby star?

EDIT: I got thumbed down, so I removed the details. The question is already crystal clear, IMO.
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2answers
735 views

What is the highest useful magnification todays largest telescopes can offer?

I know that the maximum (useful) magnification is limited by the diffraction limit, but I was not able to find numbers for the highest useful magnification factors using modern large telescopes. How ...
1
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1answer
177 views

How would a very nearby supernova shockwave and remnants affect the earth?

I've been reading about supernovae for a while, and I noticed how incredibly fast their shockwave and remnants travel shortly after the explosion. So I thought about how this would affect the earth if ...
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1answer
2k views

Energy and probability for the particle in a box

The question statement: we have a particle of mass m in a box of length a. The wavefunction is given as $$\psi(x)=x\sin \left(\frac{\pi x}{a}\right)$$ It asks to normalize the wave function and find ...
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2answers
212 views

Is there a definition of force? [duplicate]

Well, Newton's three laws talks about forces, but no definition is given. In truth, Newton's second law gives an idea of what total force is: the time change rate of momentum. But, if we have a force ...
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2answers
200 views

Complex Versus Real Wave Velocities in Quantum Mechanics

There's a fantastic quote in Schrodinger's second 1926 paper1 that apparently provides some motivation for the discrete energy levels (I think) that I'm having trouble interpreting: I would not ...
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2answers
324 views

Deriving the Lorentz force from velocity dependent potential

We can achieve a simplified version of the Lorentz force by $$F=q\bigg[-\nabla(\phi-\mathbf{A}\cdot\mathbf{v})-\frac{d\mathbf{A}}{dt}\bigg],$$ where $\mathbf{A}$ is the magnetic vector potential and ...
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1answer
152 views

Extremizing a Hamilton-Jacobi Equation

How can one make sense of the idea of extremizing a Hamilton-Jacobi equation? In Schrödinger's paper "Quantisation as a Problem of Proper Values I" (Annalen der Physik (4), vol. 79, 1926, p. 1, ...
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2answers
451 views

What's the relationship between weakly hypercharged bosons and Higgs bosons?

In this video, Leonard Susskind does a good job trying to explain succinctly the Higgs field and exactly how it gives elementary fermions mass, except for one point he seems to skip a few things. The ...
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1answer
495 views

Covariance of the Dirac equation and Infinitesimal Lorentz transformation

Okay, I've got really desperate now. I've spend 10 hours of work (for a few days) trying to prove 'trivial' equation in Quantum Electrodynamics. To anybody who want to write an answer for my questions ...
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1answer
210 views

Spinor formalism in QFT

We can describe fields by two formalisms: vector and spinor. This is the result of possibility of representation of the Lorentz's group irreducible rep as straight cross product of two $SU(2)$ or two ...
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1answer
301 views

Why do humans like to break the second law of thermodynamics? [closed]

Roughly speaking, Entropy is a measure of the disorder of a system. However as humans, we tend to do the complete opposite. For instance, in a home if a painting that is hanging on the wall is ...
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1answer
63 views

Glass properties

This is a question about the properties and strength of glass. I know that glass is an amorphous solid but I am not sure if that is relevant to my question. My question is that if there's no physical ...
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2answers
240 views

Calculate the polarization vector on reflection or refraction from a dielectric interface

I am interested in ray-tracing polarized photons. I have code that works very well for unpolarized light. When a ray hits a dielectric interface the photon is either reflected or refracted by ...
1
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1answer
542 views

Resonance Experiment

Today in high school physics class, we performed an experiment on the resonance of sound, with a set up like this... To put it simply, the sound waves are supposed to rebound with the surface of ...
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2answers
295 views

A simple question on $SU(2)$ gauge transformations in Wen's papers on projective symmetry group (PSG)?

Recently I am studying the projective symmetry group (PSG) and the associated concept of quantum order first proposed by prof.Wen. In Wen's paper, see the last line of Eq.(8), the local SU(2) gauge ...
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1answer
185 views

Voltage reading between hand and 3.3V source is only 0.1mV. Why?

I held one multimeter probe to a 3.3V source, the other probe I held in my hand. The voltage measured between these 2 points was around ...
1
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1answer
224 views

A question from a Physics 2 exam: About electron cloud an a constant external field:

I am trying to prepare for my exam in Physics $2$, the following is a question from an old exam (the question also have a detailed answer to it, but I don't really understand it). An acceptable ...
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1answer
190 views

Defining Euclidean global AdS

How does one see that that the Euclidean AdS is the same as the hyperbolic space at the same dimension ie $EAdS_n = \mathbb{H}_n = SO_0(n,1)/SO(n)$? Or is this to be seen as the definition of ...
1
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2answers
446 views

Boundary between supercritical fluid and gaseous phase

As far as I understand, going around the critical point, it is possible to transform a liquid into a gas without seeing a phase transition. Does this also mean that there is no clear separation ...
1
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3answers
249 views

If there's no atmosphere in space shielding from particles, why is not dangerous for spaceships/humans?

Some time ago I was thinking about this. We know that space is almost matter-free, and also is plenty of particles and objects orbiting around all planets and sattellites. If objects orbit around ...
1
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2answers
299 views

Cause of electromagnetic induction?

The rate of change of magnetic flux through a surface (open) is related with the line integral over the closed loop binding the selected surface by one of the Maxwell's equation. But that means even ...
1
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1answer
79 views

Question on expression in “J.S.Bell : On the Einstein Podolsky Rosen paradox”

I have a question on the article J. S. Bell, On the Einstein Podolsky Rosen paradox, Physics 1, 195, 1964. (link) My question concerns the expression (3) of the ...
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3answers
97 views

Predicting the mass of the Higgs particle

Physicists in Europe said that only after combining data collected at a laboratory in Switzerland with data collected at a laboratory in the U.S, were they finally able to announce the discovery of a ...
1
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1answer
119 views

How is a wormhole formed by spacetime surgery?

How is a wormhole formed by performing surgery on spacetime?
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1answer
165 views

A Energy Eigenbasis for the Potential Step

We should all fondly remember this basic undergraduate problem: A quantum particle is incident (from the left) upon a potential barrier of height V and width L. Compute the transmission and ...
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1answer
3k views

How to find the direction of the magnetic field for an infinite conducting wire?

We've got two long straight wires carrying current of 5A and placed along x and y axis respectively current flows in direction of positive axes we have to find magnetic field at a) (1 m,1 m) b) (-1 ...
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1answer
55 views

How to see timelike excitation has a negative norm from the “old covariant quantization”

I have a question in reading Polchinski's string theory vol I p 123, about the "old covariant quantization". It is said ... $\langle 0;k | 0; k' \rangle = ( 2\pi)^D \delta^D (k-k') \tag{4.1.15}$ ...
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2answers
250 views

How much physics a mathematician needs to know to study GR? [duplicate]

I'm intending to study General Relativity on my own. The thing is, my physics background is not very strong. I know classical mechanics and I know some electromagnetism. I'm familiar with Gauss' law, ...
1
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2answers
733 views

Projectile Motion Question involving a ball and a ramp inclined at an angle

The question is to finde the initial horizontal velocity of the ball at end of the ramp, where it is released. I know how to do this using gravitational potential energy and kinetic energy ...
1
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1answer
119 views

Red shift and the expanding universe

Given that the universe is expanding because space itself is expanding, is that expansion occuring in all places and on all scales? Consider a photon emitted from a source billions of years ago. As it ...
1
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1answer
3k views

Minimum height of mirror required to view image

I wanted to know the minimum height of mirror required to be able to view a complete image of a person. I considered the following setup: $HF$ is the person in question. $H$ denotes the head, $F$ ...
1
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1answer
415 views

Question about teeter totters or see saws

I have a basic enough question. Assume that one has one of those ideal see saws, i.e. the teeter-totter pivots on point source, the balance is of uniform mass etc. Now assume that one places an ...
1
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1answer
133 views

Mathematical explanation of why Higgs has a vev

If Higgs ($\phi$) is a complex doublet: $ \phi_{1}+i\phi_{2}$ $\phi_{3}+i\phi_{4}$ how do I show that $\phi_3$ has a vev but the others do not? ...
1
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1answer
200 views

What happens if we give a single electron charge to a hollow metal sphere?

I found this related question: What happens to 5 electrons on a sphere? But this question describes the case when there can only be 5 electrons on that sphere at all times. The answer linked to the ...
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1answer
97 views

Can we create a force shield using a gas that acts like a non-Newtonian fluid?

Most people know that if you mix cornflour with water it creates a liquid that if a force is acted upon it it solidify for an instant then returns to a liquid state. will we be able to create a gas ...

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