3
votes
1answer
142 views

Why are the elements of the periodic table stable? [duplicate]

I apologize in advance for the stupid question, but I was wondering about neutron decay and elements. Taking for example one of the most simple elements, Helium. Helium is made by 2 neutrons and 2 ...
-1
votes
1answer
63 views

How is the divergence of electric field related to the electric flux? [closed]

From the explanation of Maxwell's equations, I found, the flux of an electric field is mathematically represented by the by the divergence of the electric field.Then, how is the divergence of electric ...
0
votes
0answers
15 views

magnetic field due to current carrying coils

In the Helmholtz configuration, why is the magnetic field between the two coils uniform (I know the mathematical expression)? Can anyone please explain this physically? When the distance between the ...
0
votes
1answer
49 views

Four momentum in particle physics

I have seen four momentum defined in two different ways. One is $P =(E,\vec{p}c)$ and the other is $P =(E/c,\vec{p})$. Which one is correct and if they both are then why and when is it more convenient ...
3
votes
1answer
108 views

Relation between eccentric and true anomalies

If $v$ is the true anomaly and $E$ the eccentric anomaly, how can I show that $$\frac{dv}{dE}=\frac{b}{r}=\frac{\sin v}{\sin E}~?$$
0
votes
1answer
226 views

Tight binding Hamiltonian for 2D finite dimensional lattice and nanowire

The Hamiltonian of a 1D lattice having finite $N$ atoms, (if we consider one basis per atom) is given by the following $N\times N$ matrix- Here $E$ is the onsite energy and $t$ is the hopping ...
1
vote
1answer
44 views

Why wavefunction is sometimes multiplied by the radius to get probability density?

When solving 1d particle in a box, the probability density is said to be proportional to $|\psi|$, but when solving 3d orbitals, the probability density is said to be proportional to $|\psi|^2 r^2$. ...
0
votes
0answers
28 views

Chaotic inflationary model - bubble inside bubble

I was reading a bit about Prof. Linde's chaotic inflationary model of expansion of universe. He has mentioned about 'bubbles' of space time expansion. But no one has spoke about bubbles inside bubbles....
1
vote
2answers
131 views

What does diagonalization mean here?

In a gravity theory in spacetime, the metric has signature $− + +· · ·+$. Concretely this means that the metric tensor $g_{μν}$ may be diagonalized by an orthogonal transformation, i.e. $$(O^{-1})_{μ}^...
0
votes
1answer
46 views

Can an atom be formed from a combination of subatomic particles other than electron, proton and neutron (or their antiparticle)?

I have read that there are plenty of elementary particles. Can some of them form some species other than proton and neutron that are able to form a stable atom together with an electron or an electron ...
0
votes
1answer
82 views

Why is the potential energy minimal when the repulsion and attraction force between molecules is 0?

According to this potentialcurve and the other curve(?) the potential energy is minimal when the intermolecular forces equal zero. Why? How should I interprete negative potential energy in this ...
0
votes
1answer
73 views

How does potential energy relate to kinetic energy on a rollercoaster?

This is appearantly how the potential and kinetic energy are in the different positions of the rollercoaster, if I am not mistaking. However I don't understand why the total energy is energy and ...
1
vote
0answers
9 views

Behaviour of bubbles on the surface of a liquid [duplicate]

When you observe a group of very small bubbles on the surface of say, a cup of coffee, you can see that when the bubbles get close enough to the edge of the glass, the get attracted to it and ...
0
votes
1answer
37 views

Electrostatics problems

In image method we use image charge to calculate field and potential at any point and we replace induced charge by image charge.But why dont we directly calculate field and potential for induced ...
0
votes
0answers
79 views

Model of the nucleus as fermi gas

I am taking an introductory course in modern physics, and am reviewing some of the exams from previous years. In our course, we studies the Fermi gas model for electrons in a metal. In one of the ...
0
votes
3answers
102 views

What is a wavefront?

For this picture Anna wrote: "Incandescent light is incoherent because it comes from many sources and the same is true for sunlight. By passing the light through the one slit he created a single ...
7
votes
1answer
80 views

How did scientists manage to measure the charge of electron so precisely?

According to the latest CODATA reports the charge of electron is known very precisely $\approx 1.6021765314 \times 10^{-19}$. My question is: How is this charge determined with such high precision? ...
1
vote
0answers
33 views

What do we mean by live and neutral wire? [duplicate]

In our household circuit we have ac supply of 50 Hz. It means current reverse its direction in every 100th second. I think then, current flows in one direction then another.Then, why do we have live ...
1
vote
1answer
27 views

Is there any Higgs Model that has 4 Charged Higgs and 1 Neutral?

There is a 2HDM that predicts 3 neutral and 2 charged Higgs particles. There are also many more models out there. I already did some searching, but there is a large body of work here, and various ...
0
votes
1answer
69 views

Which system's mechanical energy is conserved?

As the figure shows, $m$ starts falling down from its current position at the original speed of zero. And $M$ is a curved side trapezoid. All friction can be ignored. |# <- This hash stands for ...
33
votes
5answers
6k views

How am I able to stand up and walk down the aisle of a flying passenger jet?

The energy of a moving object is $E = mv^2\;.$ That is it increases with velocity squared. I walk at say 3 miles per hour, or lets round that down to 1 meter per second for a slow walk. I weigh less ...
2
votes
0answers
24 views

Why do mesons like the J/Psi or Y exist? Shouldn't the quark/anti-quark pair annihilate? [duplicate]

q/qbar->photon is part of Drell Yan, so it's kinematically allowed. Is this somehow related to the difference in speed phenomenologically between a strong and a weak decay? As in is this annihilation ...
3
votes
2answers
159 views

Rigorous Mathematical Proof of the Uncertainty Principle from First Principles

While looking at an intuitive explanation for the Heisenberg Uncertainty Principle (related question below), there was a mention of an axiomatic approach to establishing the uncertainty principle. ...
0
votes
1answer
49 views

Is the matrix representation of the Lorentz transform the same for all 4-vectors?

If I have a four vector of the form: $$ \left( \begin{array}{ccc} T\\ \vec{X}\end{array} \right) $$ where $T$ is the analogous time component (i.e. energy, angular frequency, scalar potential, charge ...
0
votes
4answers
523 views

Can we see sound with our eyes? [closed]

Is there a type of sound within our visual spectrum that we can see with our eyes?
1
vote
0answers
72 views

Two trains collision problem [closed]

Consider two trains $A$ and $B$ travelling on a line one towards the other at speed $v_A=v_B=90km/h=25m/s$. When they are $511m$ apart the driver $A$ start braking with deceleration $a_A=1.25m/s^2$...
0
votes
0answers
85 views

How to plot graphene conductivity as a function of chemical potential and frequency

I want to plot Graphene Complex Conductivity as a function of two variables in Matlab.The variables are chemical potential and freqency, but I am not sure my code would be corect
0
votes
1answer
28 views

Confusion about the total bound charge of a sphere placed in dielectric

There is a solved exercise in which a charged sphere of radium $r=a$ is inside a dielectric material. The surface bound charge and the volume bound charge are respectively: $$p_{sp}=\vec{P}\cdot \hat{...
1
vote
0answers
29 views

What does black hole temperature mean? [duplicate]

From the title, the question is a bit open ended. Let me make it a bit simpler. 1. What region of the black hole has temperature? Is it the surface space? the region outside? . . . etc , any precise ...
0
votes
1answer
57 views

Electric field's area [closed]

How much area an electric field surrounds? since we're just able to draw the electric lines of force we sometimes think that the field is though 3d but surrounds a finite area. But is it measurable or ...
0
votes
0answers
33 views

Does an atom become positively charged as a result of Beta decay? [duplicate]

Since a neutron breaks down into an electron and a proton, and the electron is emitted as beta particles, the atom has an extra proton (protons>electrons). So, the atom becomes positively charged. But ...
2
votes
2answers
103 views

What happens during mass-energy conversion?

A mass is another form of energy. When a mass ceases to exist as 'matter', it exists as energy - in the forms of energy we generally know (light, heat). But is this so simple? When a mass exists in ...
0
votes
1answer
36 views

Ratio of force of resistance due to liquid to that due to gravity

What is ratio of force of resistance due to liquid to that due to gravity? For any object for example a ball falling in a liquid with constant velocity, what will be the ratio?
2
votes
1answer
103 views

Are low pressure and high pressure areas responsible for rain?

My understanding is that low pressure areas are susceptible to rain. However, high pressure areas have no rain. Now, I want to correlate this with the following areas - Lower Hutt, Wellington , NZ - ...
0
votes
4answers
53 views

Confusion regarding the forces in a system of particles

I think the internal forces in a system of particles is zero. But is it possible for the sum of internal forces to be non zero in any case?
0
votes
1answer
145 views

Two mass spring system

The equations of motion of the spring mass system with, m = 1 $ \ddot{y_1} = -k_1y_1 + k_1(y_2-y_1)$ $ \ddot{y_2} = -k(y_2-y_1) - ky_2$ My question is with the second term in the first equation. I ...
1
vote
3answers
315 views

Does quantum mechanics break causality? [duplicate]

If quantum mechanics is probabilistic, there is no reason for a particle to be in one place and not the other, but particles do make up their minds... but how?
1
vote
0answers
63 views

Theoretical magnetic Monopole

I'm trying to solve question B2 on the 2012 USAPHO semifinal exam (last page). The solutions are here on the last three pages. I don't understand the following line: The flux through the loop ...
0
votes
1answer
39 views

Tunnel through center of the earth, how to find period using $ adx=vdv$?

Suppose the boulder enters a tunnel dug through the center of the Earth along a diameter starting at rest. How would one calculate the time it takes for the boulder to reach the other end of the ...
2
votes
3answers
131 views

What changes in the electrons before and after a voltage drop?

It is easy to visualize gravitational potential energy as a function of the position of height, and a change in this potential is manifested in a change in height. Further, by the work-energy theorem ...
0
votes
1answer
74 views

Does Gauss's law not hold when there are charges outside of the Gaussian surface?

For example, if I have a gaussian surface and a negative charge somewhere outside that gaussian surface, there's going to be a non-zero electric flux. However, According to gauss's law, electric ...
1
vote
1answer
108 views

Does the property of being “virtual” for a particle depend on the observer?

I've read at several places that a static magnetic (and electric for that matter) field can be thought of as made by virtual photons, at least that's what I understood. Now, in Special Relativity we ...
1
vote
0answers
34 views

Basic Vector field question about notation [closed]

I am taking my first class in electrodynamics and the problem I am working on has a notation I have never seen before Consider a vector field of the form $V= f(x)y + g(y)x$ Is this essentially the ...
0
votes
0answers
74 views

Confusion regarding step in Einstein's 1905 paper on the electrodynamics of moving bodies

Could someone explain this step in Einstein's 1905 paper on the electrodynamics of moving bodies. I tried differentiating both sides of the first equation and still don't arrive at the second one, ...
1
vote
2answers
36 views

Why is the sound channel in the ocean especially good for low frequency sound?

Why does not the high frequency sound propagate as far? The dispersion curve $\omega(k)$ is almost linear, right?
1
vote
1answer
116 views

Understanding the delayed choice quantum eraser from a quantum information stand point

A continuation of Understanding the quantum eraser from a quantum information stand point What quantum circuit would correspond to delayed choice? In particular, the decision of whether to not to ...
1
vote
1answer
59 views

What would it be like if the supernova ASAS-SN-15lh was in the Milky way?

I'm simply wondering what it would be like if the super nova ASAS-SN-15lh (http://www.sciencemag.org/news/2016/01/universe-s-most-luminous-supernova-was-50-times-brighter-milky-way) was in our milky ...
0
votes
1answer
42 views

How much mass should be removed from balloon

If a hot air balloon has a mass of 310 kg and it is motionless due to an upward buoyant force, how much weight should be removed to obtain an acceleration of 0.15m/s^2 upward. I am not sure how to ...
0
votes
0answers
29 views

A question about the sound channel in the ocean

The sound channel (SOFAR channel) in the ocean is about 1000 meters below the surface. It is said that sound can get trapped in this channel and propagates thousand kilometers without dissipation, ...
0
votes
1answer
49 views

Not sure how to solve a problem from online course [closed]

I'm not sure how to approach this problem. I don't know the magnitude of F1 or F2 and I'm not sure how to get it from F. Any help would be appreciated.

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