1
vote
1answer
23 views

Can electrons within a positive ion absorb and reflect light?

I understand that in a crystalline metallic structure, such as one making up a bar of gold, there are one, or more, valance electrons of each atom that have left their outer shell (became free ...
2
votes
2answers
30 views

Can charge flow to a neutral body?

If an electrically positive object is kept with a neutral object, in which direction will charge flow? Will charge flow from positive to neutral until both have equal charges, or will nothing happen ...
0
votes
1answer
38 views

How Much Weight Would This Put On The Legs Of A Desk? [on hold]

first time on this site and I need help with this, I got 2 stands 1 is longer and goes top of the other. The top of the stand will have 70 lbs on it and I want to know how much pressure (if that is ...
0
votes
1answer
29 views

Question on the degeneracies of a thermodynamic system

I think I have a basic understanding of what degeneracies are: Two or more different states of a quantum mechanical system are said to be degenerate if they give the same value of energy upon ...
1
vote
1answer
9 views

dry adiabatic lapse rate

Adiabatic lapse rate is defined as $$ \Gamma_a \equiv -\left(\frac{dT}{dz}\right)_{\rm parcel}=-\frac{R_{\rm a} T}{c_p \,p}\left(\frac{dp}{dz}\right)_{\rm parcel} = \frac{g}{c_p} $$ $R_a$ is gas ...
-5
votes
0answers
17 views

Help finding peak electron concentration? [on hold]

Any tips or thoughts on how to do this problem? Thank you!
2
votes
0answers
42 views

Identifying Lorentz Covariant Equations

Statement: $\phi , A^{\mu}, T^{\mu \nu}$ are a Lorentz scalar, vector, and tensor. Which of the following equations are Lorentz covariant. a. $\phi = A_{0}$ b. $\phi = A^{\mu}A_{\mu}$ c. $\phi = ...
0
votes
1answer
19 views

Calculating Rolling friction of a car's wheels (NOT ON AN INCLINE)

I'm dealing with a small toy car consisting of a bottle that has a small hole in the back, covered by a thumb tack. The bottle is filled with pressurized air then the thumb tack is released, releasing ...
0
votes
1answer
26 views

The dot product integral in the proof of the Parallel axis theorem

The first picture is a question about proving the Parallel axis theorem and the second is the solution. I have no problem with the solution except for the part which says that $$ \int 2\vec h ...
1
vote
1answer
50 views

How do I remove the negative sign from this derivation?

A homework problem required me to show that the first equation below can be written in the form of the second equation. It was all fairly simple except for the negative sign. I'm not sure how this is ...
1
vote
1answer
21 views

Density parameter (cosmology) as a function of redshift

Hopefully I'm missing some very basic algebra for this question. In essence, I need to derive the following: $$ \Omega=\Omega_{1}\frac{(1+z)}{1+\Omega_1{z}} $$ Now, I proceeded from the Friedmann ...
0
votes
1answer
33 views

work done in reversible and irreversible process

According to maximum work theorem work done maximum work is done during reversible process . consider a reversible adiabatic and irreversible adiabatic process that occurs between two states of the ...
2
votes
1answer
17 views

How quickly does the temperature rise in a water container submerged in a hot water bath?

Let's assume I have a small bottle (neglecting any insulation from the walls of the bottle) containing e.g. 150ml water at 4°C and place it in a larger pot with sufficient water at 80°C so that the ...
1
vote
1answer
49 views

Why is it difficult for 2 black holes to merge?

Apparently as part of the merger of galaxies, sometimes the central supermassive black holes of colliding galaxies get really close, however once they come to a distance of about <1 parsec, it ...
0
votes
2answers
32 views

Some Clarifications about Electricity

In the diagram below (ignoring the text), does the $V$ mean that there is some electric field outside of this system which results in a potential difference of $V$ between $a$ and $b$ or does it mean ...
3
votes
0answers
42 views

Multiple Intersecting Universes [on hold]

I am not a relativist or cosmologist, so this is very qualitative: I imagine a pair of universes, where each has two spatial dimensions (plus time), embedded in a 3-D (plus time) space, and these ...
0
votes
2answers
24 views

Why is the intensity of an alpha ray constant along a material?

I'm taking a course in radiation physics and I've come across the following problem: A thin beam of alpha particles of intensity $I_0$ and energy $E_0$ impacts in a material. What is the intensity ...
4
votes
1answer
102 views

Help needed to understand “On the reality of the quantum state”

I am having trouble to understand the reasoning in the following paper, On the reality of the quantum state. MF Pusey, J Barret and T Rudolph. Nature Phys. 8, 475–478 (2012); arXiv:1111.3328. ...
3
votes
2answers
55 views

shape formed by a stiff string with ends pinched together [on hold]

Suppose I have a string of length $L$ with a bending energy given by $$E=\frac{1}{2}\epsilon \int_0^L ds\, (\mathbf{R}''(s))^2 $$ Let's say I form a bight with it by pinching the ends together, ...
0
votes
2answers
31 views

Damped Pendulum (generalised)

I know the differential equation for the swinging of a simple pendulum: $\displaystyle\frac{\partial^2\theta}{\partial t^2} + \left(\frac{g}{L}\right)\sin\theta = 0$ where: $L$ is the length of ...
0
votes
0answers
22 views

Water volume vs. pressure [on hold]

I have a pump that can deliver 14000 liter per hour. It is rated for a lift of 6m and a push of 36m. It has a 4m long 25mm hose as inlet(fed from a 30,0000l tank) and a 25mm outlet connected to 2m ...
0
votes
0answers
46 views

Kinetic to Electric Energy

Not the best with understanding the formulas involved with the calculations but here is the gist: I want to use Faradays law to convert the kinetic energy from actions such as shaking to produce ...
2
votes
2answers
68 views

Element 137 - Theoretical limit [duplicate]

I've seen a few sources that mention the speed of an electron in a hydrogen atom is 1/137 the speed of light. This article also mentions what looks like a correlation between atomic number and the ...
-1
votes
2answers
73 views

Is there a natural source of Antimatter in this universe?

I was just asking if there is an natural source of Antimatter in this universe capable of creating simple molecules/compounds? So, any good answers?
2
votes
5answers
89 views

Is QM something that belongs to all relative small particles or only to subatomic particles? [on hold]

For us human beings subatomic particles like elektrons are described by the laws of QM. But imagine their is a very huge giant looking on the universe. For him all the planets and stars are so tiny ...
0
votes
0answers
40 views

Feynman exercise - crystal lattice

Can you explain why there is no crystals with a shape of regular pentagon? (Usually wall of crystal have shape of triangles, squares or hexagons). Could it be a correct solution? Let's assume that ...
2
votes
0answers
31 views

Why do some stars actually produce “Gamma ray bursts”?

I looked it up but I haven't found any explanation as to why some stars produce them, I understand that collapsing and merging stars produce them, but my question is why is the energy concentrated in ...
0
votes
3answers
37 views

Motion in vacuum

If we have a hollowed sphere in a vacuum, and its hallow space is filled with vacuum. In the center of the hollowed space inside the sphere is a ball. If we push the sphere does the ball move? (prior ...
0
votes
0answers
9 views

What is the velocity of a given ion in aqeous solution?

I have seen many calculations of the velocity of X element in air at a given temperature. It has a nice closed equation: v(O2) = √ (3kT/m) However I am unsure where to look for the velocity of ions ...
-2
votes
0answers
54 views
-1
votes
1answer
34 views

Conservation of momentum wrt center of mass

"A person with mass m is sitting on one end of a lifeboat of uniform density. Mass of lifeboat is 3m. The person then walks a distance of L to the other side of the lifeboat. Which of the following ...
0
votes
0answers
30 views

Obtain an exact expression for the heat capacity of the system

Before anyone mentions it, yes I did my research and found this question on this site. My question is his exact question, but I'd like some clarification or maybe a bit more explanation than the one ...
1
vote
4answers
66 views

How to explain to a child why can acceleration be positive or negative? [on hold]

I want to find out how can acceleration be negative? I have an answer and this answer is: $$a=\frac{v_f-v_i}{t_f-t_i} < 0$$ because $v_f < v_i$ where $v_f$ is final velocity and $v_i$ is ...
-4
votes
0answers
37 views

Are there some explication for the wave function in Quantum Mechanics? [on hold]

I start to learn the Quantum Mechanics and I don't really understand the mechanisme behind the wave function. As what I feel and as I think the world as multivers, 1/ I see wave function like a way ...
1
vote
0answers
25 views

Density of states for graphene

I have seen a lot of plots for the density of states for graphene: but have been unable to find the calculation explicetely. I know the dispersion relation for graphene is $E_{\pm} (\textbf{k}) ...
1
vote
0answers
27 views

How to solve this problem : A glass sphere of radius 1 m and refractive index 1.5 is silvered…? [on hold]

Problem: A glass sphere of radius 1 m and refractive index 1.5 is silvered at its back. A point object is kept at a distance of 1 m from the front face, as shown in the figure. Find the position of ...
0
votes
2answers
36 views

Equivalent spring constant of setup

A mass $M$ is suspended using two springs having spring constant $k_{1}$ & $k_{2}$ with distance from mass as $a$ & $b$ respectively. Find equivalent spring constant of system. So I ...
-3
votes
0answers
82 views

Тhere is at least some proof that vacuum is able to propagate light? [on hold]

The "perfect vacuum" not exist. Right? Who writer said first that "vacuum is able to propagate light" and where is the evidence for this? Question is unclear for some users with rating > 17K ? No ...
0
votes
1answer
31 views

“Mass is a measure of an object’s ability to resist motion or movement of any kind”

This statement is presented as wrong, but I dont understand why. Specifically, what is the diff between motion and "movement of any kind"? Its to do with a question about inertia. I understand that ...
3
votes
2answers
41 views

Is it possible that a plane in turbulences has more downward acceleration than gravity's

In multiple Hollywood movies and TV shows I've seen scenes where a plane enters turbulences and for a moment the people in the plane seem to move upwards relative to the plane. As far as I know, as ...
0
votes
0answers
40 views

Spinor on an eigenstate of $J_z$ [on hold]

The state of a particle with spin 1/2 is described (in the $S_z$ representation) by a spinor $[\Psi]=\left( \begin{array}{c} \phi_+ \\ \phi_- \\ \end{array} \right)$ Its known to be eigenstate of ...
-2
votes
1answer
38 views

How many electrons pass trough a wire? [on hold]

How many electrons pass trough a wire if I = 6,4 Amps in 15 seconds? Can you do it step by step?
0
votes
0answers
8 views

Zero Field Magnetic Susceptibility of BiSCCO

I have been searching in the literature, with no results, for the (Zero Field) Magnetic Susceptibility of BiSCCO, but I cannot find any article regarding that. Does someone have a reference that ...
1
vote
1answer
28 views

In the orthonormal tetrad method, what is the relation between basis one forms and commutation coefficients?

If $\omega_i$ are dual basis one forms corresponding to an orthonormal tetrad basis $e_i$, and given that the commutation coefficients $C_{ij}^k$ are defined by \begin{equation} [e_i,e_j]=C_{ij}^k ...
0
votes
2answers
26 views

Work done by a friction in rolling

When force is applied on extended objects at some point, the work done by this force on this object $\vec{F} \cdot \vec{dr_{P}}$ where $P$ is the point of application of force. When the object is ...
-2
votes
0answers
31 views

Reducing a vector calculus relation [on hold]

Someone can help me? I want to reduce this. $$ (\nabla \times \mathbf{B}) \times \mathbf{B} + (\nabla \times \mathbf{B}) $$ Thanks
0
votes
1answer
31 views

Can point mass have vibrational motion?

Can a point mass have vibrational motion. I have read that reason for point mass is to ensure that we can idealize translational motion and don't have to worry about rotational and vibrational motion. ...
0
votes
1answer
28 views

Number and energy density integrals in cosmological thermodynamics

I am working through Mukhanov's book "Physical Foundations of Cosmology" and something has me puzzled in the section on evaluating integrals for number density, energy density and pressure. The ...
0
votes
0answers
19 views

specific heat capacity (temperature) [on hold]

A 60KG bushwalker is suffering from hypothermia, having an average temperature of 33.5degrees.when rescued she was wrapped in a warm blanket and given two 310ml cups of warm tea each at a temperature ...
1
vote
1answer
52 views

Michelson Morley experiment - why is there an interference pattern in the first place?

In descriptions of the experiment, the two arms of the interferometer have the same length. There's an interference pattern which was expected to be shifted when the system was rotated 90 degrees. But ...

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