# All Questions

314 views

### Having trouble understanding the concept of current and Ohms law

Circuit in series: $10\,\text{V}$ power supply, 2 resistors connected. Each resistor is $10\,\Omega$, total of $20\,\Omega$ resistance. If I put an ammeter at the end of the circuit, will the current ...
206 views

1k views

### Where's the missing helium in the Universe?

I'm confused: Big Bang nucleosynthesis is adamant about the 1 neutron to 7 proton ratio which yields 75% hydrogen to 25% helium (with a nominal amount of partially-reacted deuterium and heavier ...
107 views

### Toroid moments tensor decomposition

I am currently working on my bachelor's thesis on the anapole / toroidal moment and it seems that I am stuck with a tensor decomposition problem. I have actually never had a course about tensors, so ...
45 views

### Subnuclear physics vs wave function

This question is more a philosophical question than a physics one. When we appreciate particle physics we study that in order to explain some experimental results we have to introduce a new particle ...
200 views

### Why are popcorn seeds soft after popping?

When a seed of popcorn is heated up in oil, it pops like this: You can take one of these popped pieces and eat it with little to no problem. However, if you get an un-popped seed and sink your ...
327 views

### Nonzero ground state energy of the quantum harmonic oscillator [duplicate]

Since $\frac{1}{2}\hbar \omega$ is the zero point energy of the ground state of the harmonic oscillator, then there is no way to extract this energy. Therefore, in what way is this value different ...
92 views

### Size of an image formed by a concave mirror

A short linear object of length $b$ lies along the axis of a concave mirror of focal length $f$ at a distance $u$ from the mirror. What is the size of the image? what i have done so far: since ...
313 views

### If nothing can travel faster than speed of light then how the Universe is only 13.7 billion years old? [duplicate]

The light would take 93 billion years to reach the edge of universe but nothing can travel faster than the speed of light not even the big bang?
150 views

So we know that the EMF is induced by change of flux. The thing that was always confusing me is the following: we start changing the magnetic field which in turn induces electric field which makes ...
128 views

### Is it possible to find the hydrogen atom's radial wavefunctions?

Is there a way to actually find the equation of $R(r)$ without looking at a table with these equations already given? I'm given $n$, $\ell$, and $m$.
36 views

### Neutrino mass difference and mixing angles

What are the most recent values of the mixing angles associated with the 3 neutrinos flavors and what are their mass differences? Have they been measured in the first place?
124 views

### Quantum Logic and Quantum Field Theory

Quantum Logic is a very interesting and powerful answer to the problem of Quantum Mechanics foundations. Nevertheless this approach is usually developed in a non-relativistic framework. Is it still ...
171 views

### If we connect a source of electricity in a large water body ,will it be dangerous? [duplicate]

I was wondering whether a person will be electrocuted if he is in large pool or a sea which is connected through a source of electricity . As sea water is saline it will conduct electricity so will it ...
46 views

### How come evaporation is possible? [duplicate]

If I have wet clothes and put them on the ground and let the Sun shine on them, they dry as water evaporates. But water should evaporate at 100 degrees Celsius so how come they go dry if it's just ...
111 views

### Point source approximation

I have a 0.05 mm radius sperical source of Photons, and a 10 mm X 10 mm detector aligned to be orthogonal to their distance vector. Distance is D $\approx$ mm. I want to know how good the point ...
107 views

I learned that power intensity in EM (electromagnetic) radiation is $$I=\frac12c\varepsilon_0E_0^2$$ This equation implies that the energy in EM radiation is frequency-independent I also learned ...
236 views

### VEV of tensor fields

Is it possible to have a VEV (vacuum expectation value) for tensor field? I am mainly concerned about second rank tensors. It seems it can have a VEV which will be proportional to the metric tensor ...
59 views

### Lorentz force, multiple conductors?

3 conductors are placed in a magnetic field $B$, that have equal current $I$ flowing, is the Lorentz force totaled as the sum of all those conductors? Assuming that all of them have the same direction ...
135 views

### Gauge symmetry for p-forms

It is well known that the Lorentz invariance of the S-matrix implies gauge redundancy for 1-forms or 'photons'. Does this argument go through to $p$-forms? That is, does Lorentz invariance of the ...
157 views

### NO Uncertainties for particles in their own frames!

Well I had this thought experiment in which a particle observes itself, and something like the following is observed. Taking in mind the uncertainty principle all particles even stopped at 0K jiggle ...
87 views

### How can we know that a black hole exists? [duplicate]

How can we know that a black hole exists if it attracts both matter and light, and to prove that it exists would need to observe it? It's a very common question but I don't know the answer.
4k views

### Homemade salad dressing separates into layers after it sits for a while. Why doesn't this violate the 2nd law of thermodynamics?

The oil, vinegar and other liquids in homemade salad dressing separate into layers after sitting for a while, making the mixture become more organized as time evolves. Why doesn't this violate the ...
142 views

### What does it mean to have infinite negative conformal time?

In the context of Inflationary Cosmology, it is postulated that there was a period of shrinking Hubble Sphere radius $(aH)^{-1}$. $$\frac{d}{dt} (aH)^{-1} < 0$$ Then the regions of the ...
64 views

### Where does the potential energy associated with the field go if it is removed? [closed]

I have an electric field and a certain charged particle in it that has a certain potential energy associated with it. Where does the energy go if I remove the field?
36 views

### Can low end hepa vaccums still clean near all of the air?

In the US HEPA filters will remove 99.97% of particles sized 0.3 microns. In Europe HEPA filters do not have to meet this exact figure and there are different classes of HEPA filters e.g. h10(removes ...
404 views

### The “replica trick” initial formula?

In Spin-glass theory for pedestrians by Castellani and Cavagna, the initial formula used to introduce the replica trick is written as: \overline{\log ...
The geometry of my semiconductor device is given below. The blue regions are gold, the grey ones - gallium arsenide (n-doped to $2.9 \times 10^{15} \mathrm{cm^{-3}}$). The dimensions are μm, i.e. it ...