# All Questions

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### Why closed bottle change its weight when I put effervescence tablet?

I use several shape, several type of material (glass, metal, plastic), I use two different balances with 0.01g of accuracy. I put oil on gasket, and put upside down (like that I can see if water ...
64 views

### Quantum mechanics and second law of thermodynamics

Recently I came across this idea of Gibbs that, it is the coarse-grained entropy that always increases, whereas the fine-grained remains a constant. So classically, coarse graining refuses us some ...
478 views

### Do gravitational waves cause time dilatation?

The effect of gravitational waves in transverse traceless gauge on matter is represented by the expansion and contraction of a ring of test particles in the direction of polarization of the wave. ...
129 views

### Why is the Fermi coupling constant always expressed in units of $(\hbar c)^3$?

Everywhere I've looked so far (such as NIST) the Fermi coupling constant $G_F$ is always expressed as $$\frac{G_F}{(\hbar c)^3} = 1.166 364(5) \times 10^{-5} \textrm{ GeV}^{-2}$$ never as just ...
78 views

### How does lightning flip a car?

http://www.standard.co.uk/news/london/car-flips-into-air-after-being-struck-by-lightning-in-freak-electrical-storm-accident-10366208.html and a few others ...
10 views

### Twin and Detwin Crystals [on hold]

Hello i would like to ask , what are twin and detwin monocrystals? what has to do with their crystalographic symmetry? any consequences ? any image also would be really helpfull! Thank you
26 views

### How does lightning make Ozone?

Oxygen is found as 2 molecules. How is O1 molecule taken from 02 and then combined to make 03 by lightning?
530 views

### Why are solar eclipses more common in the southern hemisphere?

I've seen the claim that solar eclipses are more common in the southern hemisphere than the northern hemisphere and would like to understand why and if that is the case? Does it relate more to the ...
27 views

### Which force accelerates product particles in nuclear reactions?

In nuclear reactions, the difference between the binding energy of the reactants and that of the products is converted to the thermal energy of the products. Is the Coulomb force that actually gives ...
714 views

### String theory from a mathematical point of view

I have a great interest in the area of string theory, but since I am more focused on mathematics, I was wondering if there is any book out there that covers mathematical aspects of string theory. I ...
60 views

### The cosmological constant as a Lagrange multiplier?

The cosmological constant $\Lambda$ can be introduced into the gravitational action like this : S = \frac{1}{2 \kappa} \int_{\Omega} (R - 2 \Lambda) \sqrt{-g} \; d^4 x + \text{matter ...
18 views

### Measuring spin with Stern-Gerlach apparatus

I have a beam of electrons prepared in the state $|\Psi\rangle = cos(\theta/2)|+\rangle_z + sin(\theta/2)|-\rangle_z$ passing through a Stern-Gerlach apparatus which is free to rotate along the ...
26 views

### Equations of above three variables cannot be solved with dimensional analysis. What does that mean?

I came across this statement while Googling about dimensional analysis. At first I thought that I understood what the statement meant, but now I realize that I really have no idea. What does the ...
32 views

### Tension at different points of a string during vertical circular motion

For a vertical circular motion, its standard to solve for tension at the 4 common points on the circle (North, South, East, West) My question is: Is it possible to solve for tension at other ...
38 views

### Convering lightning into Kinetic Energy [on hold]

If a $200,000~\mathrm{Amp}$ lightning bolt was converted into classic electromagnetic coil creating field of 599,584,907,368,000 Gauss and directly funneled to push a magnetized pellet ...
72 views

### On a molecular level, how does heat transfer take place?

When an ice molecule hits a water molecule, the water molecule adds kinetic energy to the ice molecule. Why do the water molecules lose kinetic energy? In other words, why does heat like to go where ...
26 views

### Measuring expectation value in quantum field theory and in quantum mechanics

There is a way of calculating the vacuum expectation value $\langle 0|\hat\phi|0\rangle$ theoretically in a quantum field theory like there is a rule to compute expectation value of any operator A ...
12 views

### End-point energy of the beta spectrum [on hold]

Calculate the End-point energy of the beta spectrum of the neutron (in Mev) from the neutron and the proton masses.
23 views

### Definition of electric current

As I am taught in school that electric current is the flow of electrons, but in some places I faced another definitions like transfer of energy between electrons. I thought that it is the transfer of ...
133 views

### Domains of electromagnets

I know that magnetism is due to the alignment of domains of a magnetic substance. Due to this reason, an iron bar may be magnetized by stroking it with a permanent magnet such that its domains are ...
11 views

### Water container insulation?

If I had a 2 gallon aluminum rectangular box (quarter inch wall) full of water and had it enclosed in a thin walled aluminum shell with a quarter inch spacing which would give the best insulation ...
244 views

4k views

### What is so special about speed of light in vacuum?

I will try to be as explanatory as possible with my question. Please also note that I have done my share of googling and I am looking for simple language preferable with some example so that I can get ...
A plane electromagnetic wave has the shape: $\vec{E}(\vec{r},t)=E_0\cdot cos(\vec{k}\vec{r}-\omega t)\cdot \vec{e}_y$ \$\vec{B}(\vec{r},t)=(B_1\cdot cos(\vec{k}\vec{r}-\omega t)+B_2\cdot ...