0
votes
3answers
33 views

Displacement based on acceleration in km/h$^2$

For calculation of displacement based on acceleration and time, I have the formula below: $$ x = v_0t + \tfrac{1}{2}at^2 .$$ If I get $a$ in km/h$^2$, and $x$ in km and $v_0$ in km/h and I suppose ...
3
votes
1answer
50 views

Help understanding work

I have this problem: An object with 800kg mass is lifted up 2.4m by a force $F$. How much work does the Force do on the object (gravity is the only other force acting on the object)? From what ...
-3
votes
3answers
59 views

Derivative of kinetic energy

I read that the derivative of kinetic energy=$F\cdot v$. I tried to differentiate (1/2) mv^2 with respect to time but each time I am getting $m*v$ and not $m*a*v$ which solves to $F*v$. My efforts are ...
-3
votes
1answer
21 views

Vectors and projectile [on hold]

Two particles A and B starts moving from a high point O at t=0 in the opposite direction with horizontal velocities 9 3 m/s and 4 m/s respectively. Due to earth's gravitational field the two particles ...
0
votes
0answers
34 views

Calculation of OPE in Polchinski

Consider Exercise 2.8 in Polchinski's String Theory book. We are asked to compute the weight of $$f_{\mu \nu}:\partial X^{\mu} \bar{\partial}X^{\nu}e^{ik\cdot X}:$$ I have carried out the usual ...
1
vote
1answer
59 views

Textbook on QFT in curved space-time via path integrals

I am looking for an introductory textbook on QFT in curved space-time via the path integral method. I want to understand the following: How to build a generic perturbative QFT in curved space-time ...
22
votes
3answers
4k views

Why is gravity so hard to unify with the other 3 fundamental forces?

Electricity and magnetism was unified in the 19th century, and unification of electromagnetism with the weak force followed suit, bringing into play the electroweak force. I've been told that ...
1
vote
1answer
162 views

Are the authors saying that the observer effect plays no role in Bohr's thought experiment of the Heisenberg uncertainty principle?

Here is an excerpt from Eisberg & Resnick's Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles. Here is introducing Bohr's though experiment to establish a physical origin for the ...
1
vote
0answers
47 views

Axion strings and spontaneously broken symmetry

I have two question about axion strings: Why their appearance is connected with spontaneously broken symmetry? How to demonstrate that? Why they are stable topological configurations (look to the ...
1
vote
0answers
8 views

Origin and motivation of various flavor symmetries in the neutrino sector

Flavor symmetries of various kinds (for example, $\mu-\tau$ permutation symmetry, or the scaling symmetry, or $S_3$ symmetry) are sometimes assumed between neutrino flavours to "reproduce" the ...
0
votes
1answer
45 views

What is the algebraic form of the momentum eigenstate?

I'm asking this in the context of trying to verify the equation $a^{\dagger}_{p} \vert 0 \rangle = \frac{1}{\sqrt{2\omega_p}} \vert p \rangle$. So far I have calculated $\vert 0 \rangle = ...
2
votes
1answer
98 views

What is the difference between thermodynamical equilibrium and statistical equilibrium?

I am trying to understand what is the different between thermodynamical equilibrium and statistical equilibrium, for example, between photons and electrons at the early universe. (I read through paper ...
1
vote
1answer
272 views

Force due to combination of free space and dielectric

I will make a generalized form of my question. There are two point charges $q$, $x$ distance apart. And there is a dielectric slab of thickness $t$ and of dielectric constant $K$. Should the force ...
21
votes
0answers
879 views

A dictionary of string - standard physics correspondences

Motivated by the (for me very useful) remark ''Standard model generations in string theory are the Euler number of the Calabi Yau, and it is actually reasonably doable to get 4,6,8, or 3 ...
0
votes
1answer
586 views

Relationship between electrical resistivity and density

I just read this answer on EE.SE and that triggered a doubt in me. If I were asked whether there is any relationship between the electrical resistivity and the density of a substance I'd answer ...
0
votes
2answers
33 views

Possible values of an observable are the eigenvalues of an operator

Ok, so I'm beginning to study quantum mechanics. For reference, the book I'm using is "Konishi-Paffuti/Quantum Mechanics-A New introduction". Now, I get that the quantum state of something (say, a ...
2
votes
1answer
53 views

Continued Fraction Algorithm in Shor's Algorithm

I am just trying to make the final link of Shor's algorithm clear. Here $r$ is the order of $x$ modulo $N$. We have a number $\psi$, which for a rational number $\dfrac{s}{r}$ satisfies ...
1
vote
4answers
468 views

Is there any optical component that uniformizes the incoming light?

Is there any optical component in existence that uniformizes randomly pointing rays?
2
votes
1answer
346 views

Boundary conditions in Electrostatics

If I have a grounded conducting material, then I know that $\phi=0$ inside this material, no matter what the electric configuration in the surrounding will be. Now I have a conducting material that ...
0
votes
0answers
37 views

Proving $-\frac{\partial P}{\partial V}|_{T,N}\geq0$

I have obtained the following condition from the entropy maximum principle: $$\left.\frac{\partial^2U}{\partial V^2}\right|_{S,N}\left.\frac{\partial^2U}{\partial ...
3
votes
0answers
87 views

What physical properties of silver would contribute to the sound of a musical instrument?

A question was recently asked on Musical Practice & Performance, asking what physical properties of silver would contribute to the sound of percussion instruments. It is likely to be off-topic ...
0
votes
0answers
32 views

Measuring the spin of an electron with spin +h/2 at an axis 30 degrees off [closed]

The problem: If the z component of an electron spin is $+\hbar/2$, what is the probability that its component along a direction z' that forms an angle $\theta$ with the z axis equals $+\hbar/2$ or ...
2
votes
1answer
40 views

Relation between Von Neumann entropy (and other entanglement measures) and thermodynamical entropy

Suppose I have a bipartite system (with Hilbert space $H = H_a \times H_b$) and the following state: $$\sigma = \sum_{n} \frac{e^{-\beta E_n}}{Z} \rho_n$$ where $Z = \sum_n e^{- \beta E_n}$ and ...
0
votes
0answers
24 views

How to create a draft in a room? [on hold]

There's a room on the south side of the building, which doesn't have any ventilation vents, but have a window. Opening a window don't cause a good air circulation (by 'good' I mean that air in the ...
0
votes
3answers
69 views

Why does a change of direction imply an acceleration?

We know that it takes no energy to change the direction of a vector, we know also that it takes no energy to displace a body in motion if a push is applied exactly at a right angle on its center of ...
1
vote
1answer
310 views

Coriolis deflection:- is it 4 times if the object is thrown up, compared to a drop?

A particle is thrown up vertically with initial speed, reaches a maximum height and falls back to ground. Show that the Coriolis deflection when it again reaches the ground is opposite in ...
1
vote
0answers
27 views

Projection that keeps graviton but gets rid of B-field

We consider the closed superstring and the massless states in the (NS,NS)-sector \begin{equation} \tilde{b}^i_{-\frac{1}{2}} |0\rangle_L \otimes b^j_{-\frac{1}{2}} |0\rangle_R. \end{equation} It is ...
15
votes
8answers
5k views

What is the electric field generated by a spinning magnet?

Consider a cylinder of permanently magnetized material, with uniform magnetization pointing along the cylindrical symmetry axis (the $z$-direction). The magnet is rotating about its cylindrical ...
1
vote
2answers
107 views

Uncertainty principle in quantum field theory

Can the uncertainty principle be derived in quantum field theory? If yes, does is have a different interpretation than quantum mechanics because the coordinates $x_i$ are now parameters and not ...
2
votes
1answer
55 views

General relativity and quantum fields evolution in curved space [on hold]

There are many cases when we have to discuss the problem of evolution of quantum fields on GR background (inflaton evolution during inflation, axion field evolution etc). But GR isn't quantized as ...
0
votes
2answers
110 views

Nuclear based wireless power?

I would like to ask if there is any Nuclear process which can be used to produce a wireless power ? Is there any nuclear process can be radiate to the environment with no harm to human beings? ...
0
votes
1answer
84 views

On Thermodynamics of Spontaneity of the Reduction-Oxidation Chemical Reactions

According to the first and second law for a closed system containing different chemicals we have \begin{align} &\delta Q - \delta W = dU = T dS - p dV +\sum_i \mu_i d N_i\\ ...
25
votes
9answers
7k views

Why don't modern spacecraft use nuclear power?

The Voyager 1 & 2 spacecraft launched in 1977 with Plutonium as their source of electricity. 34 years later they claim these two spacecraft have enough power to last them until at least 2020. That ...
4
votes
2answers
120 views

In QFT how do you write down the most general interactions?

This past year I took a QFT class and I now feel comfortable solving scattering problems, but I am still a bit perplexed by how physicists write down a Lagrangian in the first place. In particular, ...
1
vote
2answers
88 views

What would a closed timelike curve look like?

What exactly are closed timelike curves. In a metric in which they would exist, what would they look like. What would it be like travelling through them? It obviously wouldn't look like a door. Would ...
2
votes
1answer
88 views

Probability current in scattering problems

This is a section from Wikipedia: In regions where a step potential or potential barrier occurs, the probability current is related to the transmission and reflection coefficients, respectively ...
-1
votes
2answers
206 views

Book recommendation for Atomic & Molecular physics

What are some interesting books for a sophomore undergrad about Atomic & Molecular Physics?
1
vote
3answers
35 views

Direction of pressure forces on a control volume (surface)

According to http://www.mne.psu.edu/cimbala/Learning/Fluid/Pressure/pressure_basics.htm, "Pressure always acts inward normal to any surface (even imaginary surfaces as in a control volume).". ...
1
vote
0answers
14 views

Neutron dipole moment and $\theta -$term

In many references is stated that by having QCD $\theta -$term, $$ L_{\theta} = \frac{g_{s}^{2}}{8 \pi^{2}}\theta F \wedge F, $$ we may compute the value of neutron dipole moment, $$ d \approx ...
-7
votes
0answers
43 views

Electricity as mass? [on hold]

Electricty is a flow of electrons said my teacher one time. Also she said: matter is something that takes up space. So I can't be in a place that has already matter. Here is where my crazy theory ...
5
votes
2answers
97 views

Physical explanations for renormalization

Some related questions on Renormalization: Why is renormalization even necessary? My understanding is that the supposed problem is that the sums of certain amplitudes end up being infinite. But ...
0
votes
2answers
84 views

Question about a car on a banked turn with no friction

A popular physics page explaining how a car can make a banked turn even with no friction : gives the following free body diagram and then says In the vertical direction there is no ...
1
vote
0answers
43 views

How did Weyl's 1918 paper; Gravitation and Electricity, influence classical physics? [migrated]

The main-stream view seems to be that Weyl's 1918 paper Gravitation and Electricity was initially considered a failure for reasons first pointed out by Einstein. But these initial ideas were reapplied ...
0
votes
1answer
165 views

How to calculate fluid(oil / hydrocarbon) loss under pressure

I'm trying to calculate the amount of fluid that would flow through an area dependant on the amount of pressure that there is. I'd also like to know the rate at which it would flow. Essentially I ...
4
votes
1answer
875 views

What parity has an electron?

I couldn't find anything about the parity of an electron. Neither in the german, nor in the spanish and nor in the english version of Wikipedia. I only found one sentence in the parity article of ...
9
votes
9answers
5k views

Hidden observers in Double Slit experiments - Do they matter?

I'm still struggling a bit with some ideas around double slit experiments. One that keeps cropping up for me is the role of observers. Imagine a classic double slit experiment with a hidden observer ...
1
vote
2answers
187 views

Use of Amperian loop to calculate the $B$-field inside a co-axial wire

The problem asks to calculate the magnetic field at point $a$ of a co-axial cable with a wire at the center surrounded by a rubber layer, and then another hollowed cylindrical wire followed by a ...
2
votes
4answers
110 views

in Newtons 3rd law, where does the second body get its energy to react?

A very basic question, and apologies if I have overlooked something obvious. In newtons 3rd law, presumably energy is transfered to the second body from the first body (which itself was subject to an ...
1
vote
2answers
141 views

Why does projecting black light from a screen mask white light shining through it?

I had a Macbook Pro, and remember being intrigued when I noticed that the apple logo on the back of the screen allowed sunlight to shine through in an Apple shape on the front of the screen when ...
0
votes
3answers
40 views

Work in the First Law of Thermodynamics

The First Law can be stated as $\Delta U=Q-W$, where $W$ is the work done by the system. My question is what kind of work $W$ includes. $W$ certainly includes $PV$ work, i.e. expansion and compression ...

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