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votes
2answers
124 views

How do we know that spacetime is uncountable/continuous/etc.?

Every major theory in physics - from classical dynamics, to quantum mechanics, to general relativity - makes assumptions about the structure of spacetime. Among the most common assumptions are that ...
0
votes
1answer
26 views

Correct relationship between the electric field and voltage at a distance from point charges

Hello I'm wondering if this is a correct understanding of the electric field and voltage strength as a function of distance. I'm helping a fellow student with their homework and I don't want to say ...
0
votes
2answers
55 views

What is the total cross section for $H \rightarrow W^{+} W^{-}$?

I need to know the total cross section for the process $H \rightarrow W^{+}W^{-}$, but cannot find it anywhere. Decay widths for Higgs decays are mentioned in Peskin and Schroeder (page 776), but I ...
0
votes
1answer
69 views

What is the most basic system that exhibits states of matter?

I'm trying to develop a more intuitive understanding of the states of matter..specifically the difference between solid and liquid. To this end, I'd like to consider the most basic system in which the ...
0
votes
0answers
18 views

What is the current in the circuit if the LED measures 2 volts? [closed]

Draw a series circuit with a 6v battery, an LED and a 330 ohm resistor. What is the current in the circuit if the LED measures 2 volts? I was able to successfully draw the circuit but I am not quite ...
0
votes
0answers
33 views

Calculating the time to perform work on rolling shutters

I have rolling shutters, e.g.: I am trying to determine how much time it takes to raise/lower the shutters a specific amount. (Because of the physics involved, the time is non-linear relative to the ...
0
votes
0answers
22 views

What difference does it make if a molecule has odd or even parity?

I've been reading a lot about term symbols and spectroscopic notation, but I must have missed the part about WHY a molecule's evenness or oddness matters, in terms of spectroscopy or whatever...
0
votes
0answers
12 views

What is the “single pulse radiometer equation”?

This document https://arxiv.org/pdf/1601.03547.pdf refers to the “single pulse radiometer equation”. Apparently, it’s used to calculate the flux of radio transients. What is the “single pulse ...
3
votes
2answers
70 views

Can a CFT have multiple primary operators with same scaling dimension and/or spin?

In CFT ($d>2$), 2-point functions (between two scalar primary operators, for example) vanish unless the operators have same scaling dimension. This leads me to wonder whether a CFT can have two ...
1
vote
1answer
41 views

Distance and time contrasting results

I know the thing I am missing is right in front of my eyes, please help me see it, I see this equation $x_{final} = x_{initial} + v_{initial}t + \frac{1}{2}at^2$. I want to find the free fall distance ...
0
votes
0answers
37 views

If I saw two gears turning in front of me, how would I know which of the two has its own turn? [closed]

If I saw two gears turning in front of me, how would I know which of the two has its own turn? In other words, one gear rotates another static gear. How do I know which gear has its own movement?
-4
votes
0answers
19 views

Calculating electrical circuits [closed]

[![Electrical circuits calculations][1]][1] [1]: Electrical components calculations https://i.stack.imgur.com/8HoSr.jpg
0
votes
2answers
38 views

Solenoid and induced electric fields

Let us suppose there is a solenoid which has $n$ turns per unit length the current is varying with time as $I =kt$ where k is a constant if the current is flowing then there must be induced electric ...
0
votes
0answers
27 views

Intensity and frequency relation [closed]

Two harmonic sound waves, of equal intensity but at different frequencies, one at $800\ Hz$ and the other at $600\ Hz$, impinge at the ear of a listener simultaneously. What two frequencies does the ...
0
votes
1answer
19 views

Resonance frequency with metal

I've made an experiment with resonance frequency of a LC circuit. One part was to place a metal (I think iron) in the middle of the induktivity of LC circuit. I measured a higher resonance frequncy as ...
0
votes
1answer
34 views

Electrostatics and Magnetostatics as Field Theories ( isn't the Coloumb law depicting an instantaneous action at a distance)

Take the formula for Coloumb's law. It does not show in any case as to how the static field propagates. What I can feel is that the field of a static charge is ever prevading from the time the charge ...
1
vote
0answers
27 views

What does Newton mean by 3 kinds of centripetal force?

In his book "Philosophiae Naturalis Principia Mathematica", Newton writes in Definition V The quantity of any centripetal force may be considered as of three kinds; absolute, accelerative, ...
0
votes
2answers
93 views

Why is the Lagrangian defined as $L=T - V$? [duplicate]

Please try to provide a sufficient answer, and when it is just „because it satisfies Newton‘s equations“, please try to give an example or explain it. If you know it, I would be very happy if you ...
0
votes
2answers
41 views

How to measure the lifetime of a particle experimentally?

I'm wondering in experiment, how can one measure the lifetime of a particle, because it is a very short time. Also, I'm wondering how experimentalists measure the mass of the particle, which is also ...
1
vote
1answer
35 views

Computations and physical processes

Can computation be accomplished using any physical process? For simplicity let me restrict myself to the computation of performing addition. I am aware that mechanical calculators just use Newtonian ...
0
votes
1answer
28 views

Super Adiabatic Evolution numerically

I'm doing some adiabatic and super adiabatic evolution using python but without success, the super adiabatic to be more precise. The problem is the way I've manage to write the super adiabatic ...
0
votes
1answer
29 views

How does a coaxial cable feed power (current) into an antenna using only one conductor? ( LogPer Antenna for ex )

I am trying to follow the power that feeds an antenna from a coaxial cable. I found this link where it explains how an dipole antenna radiate, and if I understood correctly it is used a symmetrical ...
1
vote
2answers
58 views

Why does ground reaction force decrease at the start of a vertical jump?

I don't understand why reaction force would decrease at the start of a countermovement jump. I've tried looking at this diagram and considering moments and how lowering the position of the center of ...
0
votes
0answers
22 views

Temperature dependent heat capacity and entropy

this problem is often presented as a simple demonstration of relationship between the heat capacity at constant volume $C_V$ and entropy $S$. Let's say the heat capacity $C_V$ is equal to $a T + b T^3$...
-5
votes
0answers
45 views

Will a tennis ball tossed straight up in a airplane cabin move towards the tosser or will its distance from the tosser remain the same? [duplicate]

If I am in a pressurized airplane cabin and I toss a tennis ball into the air, will the ball move towards me? My thinking is that though the ball is in an air bubble that is moving as a whole at the ...
0
votes
0answers
17 views

Spring block system on a rough surface [closed]

Suppose we have a given a block of mass m connected to a spring of spring constant k and kept over a rough horizontal surface having coefficient of friction u.Initially the spring is compressed by d (...
0
votes
1answer
36 views

When matter and antimatter meet and annihilate, is that considered 'decay'? By the EM, weak and strong forces simultaneously?

Matter-antimatter destruction is 'decay', correct? And since antimatter particles are considered the opposite of matter ones in every way, not just in terms of EM charge, does that mean they are ...
0
votes
1answer
30 views

Net torque in a system [closed]

I have a shaft that is fixed on one end and has a rotating head with 4 fans attached to it . Lets say there a propulsion device pointed perpendicular and attached to the surface of the fan in two of ...
-1
votes
1answer
47 views

How can we add torque acting at two different points? [closed]

How can we possibly add the torques acting at two different points?
1
vote
0answers
27 views

How does water move out of the way/around an object moving under water?

Let's say a torpedo moved under the water. Water is virtually in-compressible right? So what happens to the water in front of the torpedo as it pushes forward? It has to somehow move out of the way, ...
2
votes
1answer
28 views

Disconnected 2nd order terms in 2-point correlation function in $\phi^3$ theory

I'm trying to figure out a detail on the calculation of correlation functions in the $\phi^3$ theory. So, I know we can calculate a 2-point correlation function as: $$G(x_1, x_2)=\frac{\langle0|\...
3
votes
3answers
113 views

How is the frequency of a wave defined if it propagates on three different directions?

Let's consider a wave which propagates on 2 or three directions, like for instance an electromagnetic wave inside a rectangular waveguide totally closed on two ideal conductor surfaces: The walls of ...
0
votes
0answers
25 views

Is there an easy way to predict whether a given element will crystallise in the FCC or in the HCP structure?

I noticed, reading the solid state physics book by Ibach & Lüth, that the majority of elements crystallize in a handful of space groups: I highlighted face-centered cubic (FCC) structures in ...
0
votes
0answers
21 views

Equilibrium of a system “a cylinder on a cylinder” [closed]

Here is a sketch of a system There are two cylinders. It needs to find an equilibrium. What I have done: I supposed that angle between an upper cylinder and ground is a generalized coordinate. Then ...
10
votes
3answers
919 views

What do the quantum fields represent, mathematically?

I am looking for insight on quantum field theory, and more precisely, I am interested in having a low-detailed idea of what a quantum field theory is about; moreover, I should say hat I am a ...
0
votes
2answers
49 views

Confusion over the various equations of energy in basic special relativity

I have a fairly longstanding confusion over several different equations involving energy in special relativity and I struggle to see how they relate to each other. $E=mc^2$ $E=\gamma mc^2$ $E=mc^2+\...
0
votes
1answer
56 views

QFT and coordinate transformations

I was going through this lecture, where Leonard Susskind explains that these two Feynman diagrams are considered to be equivalent in QFT: One diagram explains the same phenomena in one possible way ...
1
vote
2answers
115 views

Why don't we assume a vector space structure for spacetime?

At the outset I'll state that I understand completely why, physically speaking, there's no preferred frame - that's not what I'm asking in the question. I'm not sure why we don't give spacetime a ...
0
votes
1answer
43 views

Getting the eigenvalues of a quadratic boson Hamiltonian numerically

I have the following quadratic Hamiltonian (of boson type): $$\hat{H}=\epsilon b^\dagger b -v(b^\dagger b^\dagger + b b )$$, where both $\epsilon$ and $v$ are real parameters. The operators $(b,b^\...
0
votes
1answer
16 views

What is the difference between ground state, excited state and transition dipole moment?

I need to find a transition dipole moment of Rhodamine 6G molecule, however they provide ground state and excited state dipole moment. Are they similar or can I somehow obtain transition dipole moment ...
0
votes
0answers
23 views

Relation between surface tension to mixture of liquid

I found it really intresting to read about the surface tension phenomena, and I was thinking about that if there is any relation between the percent of of liquids in a mixture. I mean if I know that $...
0
votes
0answers
8 views

Does the Sachs-Wolfe effect depart from $1/3$ for large $k$?

In the Sachs-Wolfe effect (the one at last scattering, not the ISW), the standard result is $$ \frac{\Delta T}{T} = \left( 1 - \frac{2}{3} \right) \Delta \Phi = \frac{1}{3} \Delta \Phi . $$ To ...
0
votes
0answers
42 views

Variation of the kinetic term in modified gravity

Assume you have an action $S=\int \sqrt{-g}(R+p(X,\phi)) d^4x$. I want to calculate the perturbations for $\phi(t,x)=\phi_0(t)+\delta \phi(t,x)$ and the standard perturbed metric $ds^2=(1+2\Phi)dt^2-(...
0
votes
0answers
21 views

Minimum amount of Tritium for fusion reaction producing Tritium

I'm not studying physics. I only worked with basic dynamics and have no idea how to calculate this. It's likely that the answer to the question I'm asking is nonsensical, but, from my point of view, ...
0
votes
0answers
21 views

Hyper-fine structure (Bohr's model)

I am asked to estimate the energetic splitting of the ground state using Bohr's atomic model (i.e. neglecting the Electron spins). But if we neglect the Spin and if for $n=1 (\ell=0)$ we don't have an ...
1
vote
0answers
18 views

Two dimensional conformal field theories with changing central charge

For two-dimensional conformal field theories it is usually assumed that the cental charge is fixed (for simplicity let's assume that $c=\bar c$). Is there a generalization or a concept that uses the ...
1
vote
0answers
39 views

Does the state of the holographic bulk dual of a QFT depends upon more than just the wave function?

Suppose we have two different QFTs with the same set of quantum fields which differ in their Lagrangians by a relevant operator. Assume both QFTs approach a CFT fixed point in the UV. Suppose at time $...
0
votes
1answer
58 views

Help understanding equations of motions for a line element in their full generality

(Note: I am crossposting this from https://math.stackexchange.com/q/3740738/) Let us work with these definitions $L=\sqrt{dAdB}$ and $S[A,B]=\int_{\Delta \lambda}\sqrt{\frac{\partial A[\lambda]}{\...
1
vote
1answer
21 views

Diffusion of gases of different temperature

Let a box be divided into two parts by a partition. Let each part be filled in by the same gas in equal concentrations but different temperatures. Let the gases start diffusing through a hole in the ...
0
votes
1answer
31 views

Change in ammeter's indication due to change in resistance [closed]

I stumbled on a problem in a textbook, where I was asked to describe the change in ammeter's indication due to change in resistance in circuit: rheostat's slider is moved or key is locked as indicated ...

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