All Questions

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0answers
4 views

Where does the polarity of particles come from?

Going though current lessons, I can clearly see that some particles, electrons, are charged negatively and other, protons, are charged positively. Where does this polarity come from? Knowing that ...
1
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0answers
3 views

How to model the impedance of a coil with a dielectric slab on the top

I have sketched what I meant in the image below. Were there no dielectric slab, the coil could have been simply modeled as an inductor. But I am not sure what the impedance can be if there is a ...
0
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0answers
17 views

Representations of Galilei group

Show that the operator $U(\alpha, \beta) = e^{i(\alpha \hat{x}^2 + \beta \hat{p}_{x}^2)}$ can represent the space reflection of the 1D Galilei group: $x \to -x; t \to t$. I don't really know ...
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0answers
5 views

Voltage changes under load across parallel pack

I have 97 LiFePO cells in parallel. They've been sitting for days so the voltage is equal at 3.19v. I put a 5A load on the pack, connecting + at the near end, - at the far end. I measure V across ...
1
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0answers
21 views

A question about Memristors

A question about memristors: These semiconductor entities have been defined in terms of magnetic flux leakage, and a non-linear relationship to the electric charge that has flowed. In essence, the ...
2
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0answers
19 views

How does matter interact with spacetime? [on hold]

It's easy to see how matter interacts with itself but how does it interact with spacetime which is "not" matter? Einstein showed us that mass and energy cause a curvature in spacetime, which intern ...
0
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0answers
23 views

What is the symbol for the moment of force (torque): $N$, $M$ or $\tau$? [on hold]

Classical Mechanics (Goldstein, Poole and Safko) calls it $N$. Principles of Dynamics (Donald T. Greenwood) calls it $M$. Google calls it $\tau$. So... which is it?
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1answer
13 views

Parallel Resistors (special cases formula)

Problem: A car's rear window defroster uses 15 strips of resistive wire in a parallel arrangement. If the total resistance is 1.4 ohms, what is the resistance of one wire? Solution: I rearranged the ...
1
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0answers
28 views

Ray tracing in General Relativity

I would like to find out what one would see at the Schwarzschild radius of a massive non-rotating black hole, if the black hole is surrounded by a bright ring. For that, I would place the observer at ...
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0answers
16 views

Force-carrying particles instead of forces

In which physical theories do we have such mathematical models, in which only a notion of particle is used (and e.g. the concept of force is not present in the model)? I know about e.g. gauge ...
0
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1answer
15 views

Negative pressure experiments

One method of understanding the physics of materials is to study their properties under the effect of pressure. Under high pressure, new phases can arise. Experimentally, high pressure can be obtained ...
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0answers
18 views

is the renormalization unique?

mean let be a theory A in which the divergent integrals appear $ \int_{0}^{\infty}dx $ and $ \int_{0}^{\infty}xdx $ and let be another physical theory with 3 types of divergences $ ...
0
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1answer
13 views

Does the equation for a wave passing through two slits apply for particles as waves?

The standard equation for a wave travelling through a double-slit apparatus is $w=\dfrac{z\lambda}{d}$, where $w$ is the fringe spacing at the detector screen on the other side of the slits, $z$ is ...
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2answers
27 views

What causes a resistor to heat up?

In the following video clip at 2:10, http://www.youtube.com/v/YslOUw5oueQ , Professor Walter Lewin talks about a misconception people have that the energy going through a wire to a resistor is in ...
0
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0answers
11 views

Driving force in a homopolar motor

I can't really figure out the driving force in the following homopolar motor: http://www.youtube.com/watch?v=w2f6RD1hT6Q I am not convinced by the usual argument involving the Laplace force, so ...
0
votes
1answer
29 views

What would happen if Newton's Cradle was made of other geometrical objects rather than spheres?

What would happen if Newton's Cradle was made of other geometrical objects rather than spheres? For example, what would happen if it was made of cubes and the contact area was larger?
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0answers
9 views

Modeling Temperature of a gas in a cylinder over time [on hold]

It's been years since I've done anything like this, so I'm looking for a little help. I would like to model the temperature of a gas over time while under constant pressure. Part of this is knowing ...
1
vote
2answers
23 views

Is there a difference between “No Air Resistance” and "Constant Air Resistance''?

Is there a difference between "No Air Resistance" and "Constant Air Resistance''? Like for example if we have two identical objects with different masses and we drop them from the same height. Will ...
0
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1answer
20 views

Rotation in configuration space

Let $R_\psi$ be the rotation in configuration space around a vector $\bf{e}_\psi$ for an angle $\psi$. How is that the space rotation in configuration space have: ...
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2answers
31 views

Why is quasineutrality required for a gas to turn into a plasma?

Why is quasineutrality a required condition for a plasma to exist? Quasineutrality means that no density of electrons and ions should almost be equal but not exactly equal. Can anybody explain this ...
3
votes
1answer
49 views

Bosonic Schrödinger field [on hold]

When second quantizating the Schrödinger field $$\psi(r,t) = \sum_i \phi_i(r)b_i(t),\quad\mbox{and}\quad \psi^{\dagger}(r,t) = \sum_i \phi_{i}(r)^* b_i^{\dagger}(t),$$ we have the commutation ...
1
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1answer
22 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
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1answer
27 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
30 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
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2answers
41 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
36 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
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1answer
17 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
27 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 $$\frac{m_1}{m_2}=\frac{4v^{2}_2}{v^{2}_1}$$
3
votes
1answer
59 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
26 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
14 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
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1answer
21 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
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0answers
22 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
44 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
1answer
43 views

Apparent spacetime dependence of creation and annihilation operators

I'm currently going through An Introduction to Quantum Field Theory by Hartmut Wittig I've stumbled upon. Having trouble with equation (2.29), I'm asking the question: Do creation and annihilation ...
3
votes
2answers
82 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
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2answers
52 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
19 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
16 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
2answers
38 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
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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
37 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 ...
3
votes
1answer
57 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
57 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 ...
8
votes
2answers
690 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
2answers
94 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
72 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 ...

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