# All Questions

149 views

### Do objects have energy because of their charge?

My gut feeling tells me things should have energy because of their charge, like they have energy because of their mass. Is this possible? Has it been shown? If not then what is missing to make such ...
72 views

### Higgs boson/field symmetries and local symmetries

In the SM with gauge group U(1)xSU(2)xSU(3), those factors are associated to the gauge bosons associated with a local symmetry and the Higgs field provides masses to the elementary fermions AND the ...
227 views

### Producing electricity from all wavelengths of electromagnetic spectrum

Is it possible to produce electricity from all wavelengths of electromagnetic spectrum beside visible light ?Like using gamma rays or x-rays .
497 views

2k views

### Goldstein's Classical Mechanics exercises solutions [duplicate]

Does anyone know where I can find some (good) solution of Goldstein's book Classical Mechanics?
158 views

### Potential of a conductor depends on the size and shape of the conductor. How?

1) When a charge 'q' is given to an isolated conductor, its potential will change. 2) The change in potential depends on the size and shape of the conductor. I could understand the point no. 1. ...
221 views

### Noether's identities

I have some questions about the Noether's second theorem (generally not covered by field theory books): What is the most general Noether identity for (classical) field theories? Why are Noether ...
60 views

### Gaussian surface in a charged infinite plance sheet

The following question arises on the use of Gauss law. In the charged finite sheet problem, we consider a Gaussian surface on only one side of the sheet. But, In the case of an infinite sheet, we ...
95 views

### Energy flows in the core also responsible for another of the planet’s unique [closed]

Energy flows in the core also responsible for another of the planet’s unique features: a strong magnetic field. Scientists believe that the earth has had a magnetic field for at least 3.5 billion ...
677 views

### What does it mean to integrate out fields from a theory?

I've done a fair bit of reading on this subject and I'm still confused about the basic principle of integrating out fields in QFT. When we have a function of 2 fields a and b, f(a,b), and we integrate ...
213 views

### Does Earth produce metallic elements in its core?

Does Earth produce metallic elements in its core?
958 views

### What is Transverse Energy?

What is transverse energy? Why we use transverse total energy instead of energy and transverse momentum in place of Total momentum in the particle detectors?
248 views

### How did Newton find out force has something to do with acceleration?

Its about Newton's second law of motion, $$F=ma.$$ It says the acceleration of an object is directly proportional to the net force and is inversely proportional to the object's mass. Yes I can ...
1k views

### Understanding Einstein's field equation

Einstein's field equation: $$G_{\mu\nu} = \frac{8\pi G}{c^4}T_{\mu\nu} - g_{\mu\nu}\Lambda$$ I'm trying to understand each of the terms in this equation intuitively, but I'm struggling. Basically, ...
239 views

### What is the most natural value of Heaviside step function at zero argument?

In many physical applications, the Heaviside step fuction is defined as $$H(x) = \left\{\begin{eqnarray} 1, \quad x>0 \\ 0, \quad x<0 \end{eqnarray}\right.$$ The value $H(0)$ is left undefined. ...
243 views

### We're all star dust?

OK so we've all heard of this from Carl Sagan, Lawrence Krauss and others and we know the argumentation, I don't refute that. There are other examples, for instance I once calculated (this was before ...
5k views

### What makes running so much less energy-efficient than bicycling?

Most people can ride 10 km on their bike. However, running 10 km is a lot harder to do. Why? According to the law of conservation of energy, bicycling should be more intensive because you have to ...
210 views

### Mass equals Moment of inertia when constant density?

I have found equation for moment of inertia $(J)$. I'm calculating $J$ for hemisphere, with rotational axis $Z$. $$J = \iiint\limits_V r^2 \cdot \rho \cdot dV$$ But if $\rho$ is constant ...
2k views

### Workdone in an equipotential surface is zero?

An equipotential surface is one in which all the points are at the same electric potential. If a charge is to be moved between any two points (say from point A to point B) on an equipotential surface, ...
287 views

### Concerning the curvature of an airfoil (shape)

I am wondering about the reasons for the shape of a turbine blade airfoil, see here Do you know the reason for this shape? Usually, very large curvatures like this are to extract high lift from LOW ...
91 views

862 views

### Does entanglement not immediately contradict the theory of special relativity?

Does entanglement not immediately contradict the theory of special relativity? Why are people still so convinced nothing can travel faster than light when we are perfectly aware of something that ...
120 views

### Heating and Recooling of an Object

Consider a piece of metal of length $L$ and linear thermal expansion coefficient $\alpha$. We eat the metal $\Delta T$ degrees, causing the metal to increase to length $$L' = L + L \alpha \Delta T$$ ...
922 views

### Uncertainty Principle and Energy range for an electron in an atom

I have the following exercise: Use Heisenberg's uncertainty principle and the relation $\Delta u = \sqrt{\langle u^2 \rangle - \langle u \rangle^2}$ to find the range of energy an electron has in an ...
131 views

### Looking for modern results in semiclassical physics and relevant references

What are some important approximations, especially those that are state-of-the-art, used to approximate the many-body dynamics of atoms and molecules in the semiclassical regime? To be clear, I'm not ...
499 views

### Overcharging a black hole

Hubeny's 1998 paper got a lot of people interested in determining whether cosmic censorship can be violated by dropping too much charge onto a black hole. It suggested that you might be able to get a ...
102 views

### How much refraction occurs as a fraction of all reflection and refraction?

When light reaches a boundary between materials below the critical angle, some of it refracts and some of it reflects. For example, glass acts as a partial mirror with a dark background. Assuming ...
335 views

### Semi-major axis and ellipticity of a binary system?

In the image below (source at bottom), it seems to be suggesting that $$a = a_{1} + a_{2}, \hspace{8cm}(1)$$ where $a_{1}$ and $a_{2}$ are the semi-major axis of the ...
172 views

### Quantum graph theory: complex spectra

In quantum graph theory, what are the properties of a given graph to own complex conjugated complex eigenvalues, either finite or infinite? Spectral graph theory is as far as I know a not completely ...
92 views

### Spectral properties of CFT

What are the general spectral properties of CFT? I mean what is the "spectrum"/eigenvalues of CFT in 2d and d>2 spacetime dimensions? I understand the "spectrum" and "Fock space" realization of Dirac ...