All Questions

0
votes
0answers
9 views

conditions on gas to be a plasma!

why quasineutrality is a required condition for plasma to exist? quasineutrality means that no density of electrons and ions should almost be equal but not exactly equal. Can anybody explain this ...
0
votes
0answers
6 views

Bosonic Schrödinger field

I have in second quantization the Schrödinger field $\psi(r,t) = \sum_i \phi_i(r)b_i(t) , \psi^{\dagger} = \sum_i \phi(r)^* b_i^{\dagger}(t)$ and we have that $[\psi(r,t),\psi(r,t)\dagger]= ...
1
vote
0answers
12 views

Work energy and laws of motion and friction problem?

I am having a confusion in the following question- Q-To stimulate car accidents auto manufacturers study the collision of moving cars with mounted springs of different spring constants. consider a ...
0
votes
1answer
14 views

Influence of applied voltage to an electron of a metal

I would like to ask what would happen to the potential well of an electron being trapped in a metal? If I apply a voltage trying to accelerate the electron out of the potential well. Would It make the ...
0
votes
1answer
24 views

Rotational Speeds

I was driving the other day and couldn't help but look at all the wind mills in the wind farms. I know I am not doing the math correctly, but I want to know what is "really" happening when a windmill ...
0
votes
0answers
9 views

Kinetic Friction & Horizontal Motion

Recently I have been trying to reteach myself some elementary physics that I learned long ago and have since forgot. I came to this problem today and I am not sure how to proceed: A $24kg$ sled is ...
0
votes
2answers
35 views

What is a CCD structure?

In a exam paper for entry into Oxford University for physics, I came accross something which I hadn't met before, and I have no idea what the question is asking - none of my teachers could explain it ...
1
vote
1answer
32 views

What's inside a quark? [duplicate]

What particles make up a quark? We all know quarks (3, uud) make up a proton. I read on Wikipedia they are called "hadrons" ,but how do they work? Is the collection wave functions of the components ...
0
votes
1answer
8 views

Mimic Magnetic Repulsive Resistance through a spring

I have two identical magnets and I push them towards each other so that they are repelling. Is it possible to accurately mimic this repulsion effect (magnetic energy) just using a metal spring ...
-2
votes
1answer
21 views

Question on kinetic energy, mass and velocity [on hold]

Two bodies have kinetic energies in the ratio of 4:1 They are moving with equal linear momentum. What is the ratio of their masses. My answer : I get $$\frac{m_1}{m_2}=\frac{4v^{2}_2}{v^{2}_1}$$
1
vote
0answers
29 views

How does conservation of energy manifest itself quantum mechanically?

We know that classically, if we have some theory $\mathcal{L}$ such that the action $\int d^4 x \mathcal{L}$ is invariant under time translation, then we can use Noether's theorem to find that (the ...
0
votes
1answer
25 views

Power - 1/2 Force x velocity? [on hold]

A pump, taking water from a large reservoir, is used to spray a jet of water with speed 20m/s. The nozzle of the pipe has radius 0.05m, and is level with the surface of the reservoir (no change in ...
0
votes
1answer
10 views

Question about the derivation of tight-binding model in the form of second quantization

There is a step in such derivation that I cannot follow. That is eq(1.74) in http://www.itp.phys.ethz.ch/education/fs13/sst/Lecture-Notes.pdf in page 21. How does these non-crossing terms vanish? ...
0
votes
1answer
17 views

How to find bond length from potential?

A bonding potential like the Morse potential or a Lennard-Jones potential is characterized by a distance at which the potential is minimal, referred to as e.g. 'equilibrium bond distance'. Is this ...
-2
votes
0answers
19 views

laplace equation [on hold]

Consider $u(x,y)$ satisfying Laplace’s equation inside a rectangle $R=\{0\leq x \leq L, 0\leq y\leq H\}$ subject to the boundary conditions $$\begin{array}{rclcccrcl} \frac{\partial u}{\partial ...
-1
votes
0answers
21 views

laplace equation [duplicate]

Consider u ( x,y ) satisfying Laplace’s equation inside a rectangle 0 ≤ x ≤ L , 0 ≤ y ≤ H subject to the boundary conditions ∂u ∂x (0 ,y ) = 0 , ∂u ∂x ( L,y ) = g ( y ) , ∂u ∂y ( x, 0) = 0 , ∂u ∂y ( ...
0
votes
1answer
35 views

Boundary value problem

Consider the boundary value problem \begin{align} \frac{du}{dt}&= \frac{d^2u}{dx^2} , \\ u(0,t)&=0 \\ u(L,t)&=0 \\ u(x,0)&=f(x) \end{align} I know how to solve it using ...
3
votes
0answers
20 views

Apparent spacetime dependence of creation and annihilation operators

I'm currently going through an introduction to QFT I've stumbled upon. Having trouble with equation (2.29), I'm asking the question: Do creation and annihilation operators ($\hat a^\dagger(k)$ and ...
2
votes
2answers
77 views

What is the cause of planetary rotation. Not orbital rotation [on hold]

I am a senior in high school, sixteen years old. I think differently than most in my class. Recently, I have been thinking about alternative causes for the rotation of our planets. My current thought ...
0
votes
2answers
44 views

Nondimensionalization of a simple system [on hold]

A damped spring mass system is modelled below: $$m\frac{d^2y}{dt^2}=F_s+F_d\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space\space t>0$$ ...
2
votes
1answer
16 views

Fluid flow through an orifice

Forgive me for my ignorance. What would be the method to determine the pressure a non compressible fluid creates when forced though an orifice? Keep in mind this orifice does not have a constant ...
1
vote
0answers
15 views

Is it compulsory to solve the reduced density matrix

Is it compulsory to solve the reduced density matrix to get the eigenvalus for quantifing the von-Neumann entanglement entropy? Can't we proceed without those?
1
vote
1answer
31 views

Equation of State and Neutron star

I'm searching for equation of state books, with references to neutron star and ultra-dense matter.
0
votes
0answers
38 views

Why we can't run using hands paw but easily can run using legs [on hold]

Normally we can run using our legs but we can't do the same using our hands.
0
votes
0answers
22 views

Reference for coefficient of static friction can be larger than 1 [on hold]

I am looking for some good references for the following quote from wikipedia that the coefficient of static friction $\mu$ may be $> 1$. Rubber in contact with other surfaces can yield ...
1
vote
1answer
34 views

Time derivative of $\hat p$ under time varying Hamiltonian

How does one show that $$ \frac {d\hat p}{dt} = \frac 1{i\hbar}[\hat p, \hat H]$$ is valid even when Hamiltonian is time dependent explicitly? I can see that this is true when $\hat H$ is time ...
0
votes
0answers
35 views

Questions regarding entropy

I have some questions regarding entropy: I know that entropy is the measure of the number of specific ways in which a thermodynamic system may be arranged. I know that any natural process occurs in ...
3
votes
1answer
53 views

How does path integral formulation explain bound states?

It seems to me that the intuitive explanation of path integrals in quantum mechanics describes scattering processes only. You have a particle going from A to B and you compute the probability ...
0
votes
3answers
56 views

Can you pre-determine the result of a coin toss?

The question is fairly simple. Consider the following parameters which are known to you: 1.) Mass of the coin 2.) The force applied on the coin 3.) The point where the force is applied on the coin ...
7
votes
2answers
500 views

How does varying temperature affect the accuracy of grandma's pendulum clock?

I have an antique pendulum clock(my granny's!) . If I detail it, This clock is approximately 5 feet tall and enclosed by wood and below it its glorious pendulum oscillates . It gave more or less ...
4
votes
1answer
58 views

Renormalization, integrating out high momenta Wilson way

In equation $(12.5)$ in Peskin and Schroeder, they write out the generating function but leave out all quadratic terms of the form $\phi\hat{\phi}$ arguing that they vanish since Fourier ...
1
vote
2answers
60 views

Magnetic force as a relativistic effect?

There is something I am confused about when it comes to the force between two parallel wires carrying current, specifically why when they carry current in the same direction the wires are always ...
0
votes
1answer
20 views

Direction of the particle's motion

^ y | | |--------------> x Above I have labelled the axes of the graph. In the figure we can see that the direction of the particles motion is downward ...
0
votes
0answers
22 views

Help with 4-velocity [on hold]

The 4-velocity $\overline{U}=(U^0,U^1,U^2,U^3)$ corresponds to the 3-velocity, $\underline{v}$, in the sense that $\overline{U}=\gamma(v)(1,\underline{v})$. Express (a) $U^0$ in terms of ...
1
vote
1answer
16 views

Construct classical computer using classical light

Quantum light (i.e. photons), linear optics, adaptive measurements and feed forward can be used to build an efficient universal quantum computer. ref: Knill et. al. 2001. Clearly the above resources ...
0
votes
1answer
21 views

Vertical motion initial velocity given max height

I'm having a hard time finding a formula that calculates the initial vertical velocity for a projectile that should reach a certain height. I'm using this formula to calculate both vertical and ...
1
vote
0answers
9 views

Heat dissipation of a quantum circuit of Hadamard gate and a loop

The following Q&A about reversible computing is available here. It has listed a number of practical scenarios where a reversible circuit can still be dissipating heat. Let's assume that none of ...
0
votes
0answers
8 views

the viscous hydrodynamic forces and the nonlinear viscous hydrodynamic forces? [on hold]

Are the viscous hydrodynamic forces and the nonlinear viscous hydrodynamic forces applied on offshore platform in the ocean? The platform is fixed.
11
votes
2answers
2k views

Why are a motorcycle's front brakes more effective than back?

I've noticed that when I apply the front brakes on my bike it stops quite quickly. If I apply the back brakes at the same speed, it skids rather than stopping quickly. Why?
1
vote
1answer
79 views

Can there be force without motion?

I am confused. Can you have a force or tension without motion? Take for instance two robots with jet packs connected via a cord, each is flying in opposite directions. The tension of the cord is ...
0
votes
0answers
23 views

Why does not electron cloud collapse over Nucleus? [duplicate]

Gravitational Force & Electrostatic Force should have attracted electron cloud & collapse it over positively charged nucleus.But it doesnot happen One rationale I find behind the phenomenon ...
0
votes
0answers
5 views

Minimum deviation [on hold]

A ray of light experiences a minimum deviation when passed symmetrically through an equilateral triangular prism. Calculate the angle of incidence of the ray when the refractive index of the glass is ...
0
votes
1answer
20 views

Tesla Coils - Is there a risk that the discharge can create x-rays?

I've built a Tesla coil that stands about 3 ft tall and uses a spark gap as the interrupter for the primary circuit. Judging by the size of the streamers it's reaching at least a million volts. ...
3
votes
0answers
20 views

To what extent can the superconducting order parameter be thought of as a macroscopic wavefunction?

I know that the order parameter does not obey the Schrodinger equation; it instead obeys the Ginzburg-Landau equation. However, I am unclear as to the situations under which the view of the ...
0
votes
1answer
7 views

discharging static

Quick question, if you have a buildup of static charge causing sheets of paper to stick together, can you have a grounding foil touching the paper to dissipate the charge to prevent pages from ...
5
votes
4answers
358 views

Is there a fundamental reason not to define the work vice-versa

My question arises from something which has never been really clear: in continuum mechanics, why is strain energy defined as: $$W=\int_\Omega ...
1
vote
3answers
27 views

Do electrons in absorption spectra absorb photons with enough energy to release them from their parent atoms?

Absorption spectrum theory says that electrons in the atoms absorb only photons of certain frequencies, which causes the dark lines in an absorption spectra. However, I understand that electrons that ...
1
vote
0answers
17 views

Area moment motivation

I have some intuition about the (second) moment of inertia, and there is some motivation to define this concept if we think about the $KE$ of a rotating body or the torque $\tau$ applied, for example, ...
2
votes
2answers
66 views

Is a wave packet physically realizable as a Fourier series?

In QM a wave packet is modeled as an infinite, or almost infinite, Fourier series, and the Fourier transform provides a transformation between momentum space and position space. To what extent is ...
0
votes
0answers
18 views

Forces at each point for a simple truss [on hold]

I have a truss here: It is given that the forces at point 2 are horizontally and vertically. Positive values for lowercase f forces indicate tension, and negative ones indicate compression. I ...

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