-1
votes
0answers
19 views

Voltage is taken as vector- in LCR circuit. Why

Why voltage is taken as vector( phaser diagram ) while dealing with LR, CT, LCR circuit.
0
votes
0answers
38 views

What is the physical meaning of a Partition Function in Statistical physics?

In many places in statistical physics we assume the partition function. To me the explanations after partition functions are most of the times clear but always wonder why a partition function and what ...
-6
votes
0answers
22 views

Mechanics - motion problem [on hold]

. A particle starting from rest accelerates at 2m/s2 for some time and then travels uniformly and passes a point 175m from the starting point 20m after start. The velocities of the particle at the ...
1
vote
2answers
63 views

How is Einstein's arbitrary additive constant $C$ constant during the emission of light?

This is a follow up on this question. In his paper under the title:Does the inertia of a body depend upon its energy-content, Einstein considers two inertial frames $(x,y,z)$ and $(\xi,\eta,\zeta)$ ...
1
vote
0answers
33 views

Activation energy of luminescence

Assuming that activation energy is constant for some range of temperature, it can be determined from the slope of the plot: $$\ln{I}=A-\frac {E_a}{k_bT}$$ where $I$ - intensity , $E_a$ - activation ...
1
vote
2answers
56 views

Langevin Equation - Stochastic Differential Equation. What are the subtleties?

I am trying to find out the motion of a particle in 3D governed by the Langevin equation, numerically. Anyway, the Langevin equation is given by $$m \ddot{x} = -(6\pi a\nu) \dot{x} + F_b $$ where ...
1
vote
1answer
51 views

Doppler shift from a transversely moving plane mirror

Below is the diagram of the question I have on the Doppler shift of a light emitted from a stationary light source $S$ at an angle $\theta_1$ toward a transversely moving plane mirror $O$ having ...
1
vote
0answers
56 views

How to invert this metric?

Reading this article i find a result that i am not sure how to obtain (page 3 eq 3). It is about the inversion of a metric of the type $$ g_{\mu\nu}=Al_{\mu\nu}+BH_{\mu\nu}. $$ In order to invert ...
-1
votes
0answers
20 views

Solve for distance travelled accounting for relativity [on hold]

I have: Initial speed $v_0$ Traveler time (in days) Constant Acceleration (in $m/s^2$) From that I want to solve for distance traveled, accounting for relativistic effects. I think I see how to ...
1
vote
1answer
54 views

Why is the entropy of most systems not infinite?

We can define a microstates as follows: Definition 1: A complete specification of the six coordinates of each molecule of a system, within the limits of the dimensions of the cell in which its ...
-1
votes
0answers
29 views

Is there a practical use for powerful handheld lasers? [on hold]

Not sure if this is the right forum for this, please move if appropriate. I was looking at Wicked Lasers, who offer hand held lasers with upto 2W output power. These lasers come with a ton of ...
0
votes
0answers
20 views

The universe is said to have begun as a singularity, but how do we know nothing else existed? [duplicate]

When I imagine the big bang, I first imagine a tiny ball surrounded by black void. Then the ball explodes and the universe begins. I assume most physicists have the same basic idea. But how do we ...
1
vote
0answers
37 views

Does space expansion change value when traveling near the speed of light?

To draw an analogy, we receive roughly the same amount of cosmic background radiation from all directions. However if we were to travel near the speed of light relative to the reference frame where ...
1
vote
0answers
30 views

Is potential energy frame dependent in special relativity?

In newtonian mechanics, As far as I'm aware, only kinetic energy is dependent on frames of reference, since kinetic energy is a function of velocity(squared) and velocity is dependent on frames of ...
0
votes
2answers
74 views

Why does a circle and square of same length occupy different areas? [on hold]

May be this question do not meet the standards of this blog but i was just calculating on things and i got stuck..actualy we were playing this game in which we were to fill students in a square and ...
1
vote
2answers
42 views

Can an egg be forced into a bottle by lowering the pressure inside the bottle using cold air?

I just asked a question about why ice-cold water inside a thermos results in what feels like suction on the cap. The answer stated that the cold water cools the air inside the thermos, thus slowing it ...
1
vote
0answers
24 views

Bragg Scattering of Thermal Neutrons

I'm currently reviewing Bragg scattering. The particular problem below has me slightly confused on whether I'm thinking about it correctly. Questions Is the problem below referring to the kinetic ...
0
votes
2answers
54 views

Vertical Circular motion - Tension and velocity

I read through the question Minimum velocity of the particle at the highest point which is quite similar to my questions. But I still have some doubts in the answers - "The particle will complete ...
1
vote
1answer
89 views

Why does very cold water in a thermos cause there to be strong suction on the cap?

After putting ice-cold water in a thermos, the cap is strongly held on by what feels like suction. I assume the cold water condenses the air, thus lowers the pressure inside, but can someone explain ...
0
votes
0answers
27 views

potential decomposition in terms of Bloch eigenstate

Given a single particle Hamiltonian $H=-\frac{\hbar^2}{2m}\nabla^2+V(r)$, where $m$ is the electron mass and $V(r)$ is a periodic function representing the lattice potential. It is defined in the ...
24
votes
7answers
4k views

What is Quantum Mechanics really about?

This question might sound very silly, so I'm sorry if that's the case. I'll try my best to make my point clear here. Before explaining, just to make clear, I'm not confused because of the Math ...
1
vote
1answer
36 views

Intuition about Momentum Maps

I'm studying Classical Mechanics and there is one object that appeared recently on the book I'm not being able to get a physical intuition about it. The mathematical definition goes as follows: Let ...
0
votes
1answer
26 views

What is meant by the expression “Markovian dynamics”

I know what a Markov chain is but what does it mean in physics when I say that I assume Markovian dynamics? For example in Quantum Mechanics, I read that it means that the time evolution can be ...
3
votes
3answers
472 views

Jet turbine blades from single crystals, how are they formed?

I know about nothing about crystals, although I do know a bit more about jet turbine engines, and I definitely know that you don't want the fan blade hitting the fan housing. The reason given in the ...
0
votes
2answers
22 views

Galaxy Cluster Data

I have a modification to ${\rm MOND}$ that appears to work much better than 'Standard' ${\rm MOND}$ at the galactic scale. I want to test this model now on larger structures. Does anyone know where ...
1
vote
0answers
16 views

Do lattice gauge theories with discrete gauge groups have sensible continuum limits?

In lattice gauge theories the only gauge invariant observables are constructed from Wilson loops and local field strength observables are reconstructed as zero size limits of Wilson loops. Furthermore ...
0
votes
2answers
59 views

Examples of measure zero sets in physics [on hold]

The problem with Riemann integration of functions like ${\chi }_{ℚ}(x)$ (a function which takes the value of 1 if $x\in ℚ$, and 0 otherwise) is usually used to show the need for defining the Lebesgue ...
3
votes
1answer
51 views

The James Webb Telescope, why are there 5 levels of protecting foil?

From simple curiosity, does anybody know why there are around 5 layers of solar radiation reflecting foil on the James Webb Telescope, rather than one or two? Is it to save weight, or (probably) ...
0
votes
0answers
24 views

Storing ice for HVAC

Apologies if this question is outside of the scope of the site. Assume my home is a $20 \textrm{ ft} \times 40 \textrm{ ft} \times 10 \textrm{ ft}$ block. Further assume that it has continuous ...
-1
votes
4answers
44 views

Position from a Velocity-Time graph

Find the position at t= 3.0 seconds. The initial position is 2.3 m. I found the average velocity to be 3.33 repeating so I multiplied that by the time (3) to get 10 and then added the initial ...
0
votes
0answers
54 views

Perturbation theory, eigenvalues and eigenvectors for degenerate case (1st order)

I was trying to understand the perturbation theory, but I was lost in the notation... I have understood that I have to identify the unperturbed kets that are degenerated and find the matrix $V$, ...
3
votes
2answers
239 views

State of a system in Quantum Mechanics and state vectors

I'm taking a course in Quantum Mechanics and there is something I'm not being able to fully understand. On more elementary courses on Quantum Mechanics I've been told that the idea of Quantum ...
0
votes
0answers
19 views

What is a n-type doped solar cell?

I always thought a solar cell consists of two areas, a n-type and a p-type doped one. So what exactly is meant by n-type doped solar cells? Does it not have a p-type doped area? And how does it work ...
1
vote
1answer
28 views

Need help on understanding mechanical wave function [on hold]

My textbook states that, equation 1 : y(x=0,t) = Acos($\omega$t) = Acos(2$\pi$ft), which I understand. However the book goes deeper stating also that, t-$\frac{x}{v}$, and $\frac{x}{v}$-t I am ...
0
votes
0answers
22 views

Is there a constant decay of particles that maintains the value of the Quantum Vacuum? [on hold]

By my question I am attempting to understand how the Vacuum of space remains at a constant value, (GR the universe on the large scale matches the “critical” energy density of about 8.5×10-10 J/m3) ...
3
votes
0answers
32 views

What quantum measurement formalism is easiest to implement physically?

As part of my studies and research, I have learned to work with three different measurement formalism which I define to avoid any ambiguity with the nomenclature: General measurements, which are ...
0
votes
2answers
62 views

Is the universe a Turing machine?

Reading about Computable numbers I wondered if there is any physical experiment that returns non-computable numbers or if there is any physical theory that needs non-computable numbers. Because if ...
1
vote
2answers
52 views

$ \Delta H = C_p \Delta T $

The definition of enthalpy as a function of heat capacity and temperature change. $ \Delta H = C_p \Delta T $. Does it only apply at constant pressure? In my discussions on this board and also with ...
1
vote
3answers
336 views

Is it possible to have things orbit around us?

Since humans are not large in mass, do we exert enough gravitational force for a small object to orbit around us? (Assuming that the only gravitational force acting on the object is from the human). ...
0
votes
0answers
18 views

A wave is passing through a potential barrier

Let assume a wave is passing through a potential barrier. Like this: What will be happened to the amplitude or the shape of the wave during the movement through the potential barrier? {assuming ...
1
vote
1answer
73 views

Mathematics of the Virtual Displacement

So I'm pretty certain this question has been asked to death here, but I still can't find a good explanation of a very particular aspect of the virtual displacements in physics. Background For ...
0
votes
0answers
15 views

Repulsive potential for free fermions

My question -which is probably easy to answer for a physicist- stems from trying to understand the repulsive interaction between fermions. For instance the fact that states of multifermion systems are ...
0
votes
1answer
24 views

Why, in order to obtain distinct interference, is a small distance between the two waves essential?

This is quoted from Concepts of Physics by H.C.Verma: In order to obtain a fairly distinct interference pattern, the path difference between the two waves originating from coherent sources should ...
-3
votes
1answer
59 views

Without friction, what happens in our life? [on hold]

Generally all are subject to friction. So friction is most a essential part of our life, if friction is not available in our surrounding then what would happen in our life and which technique could we ...
0
votes
1answer
13 views

why we use Gibb's free energy concept in Ehrenfest's theory of Phase transformation?

Why do we use the concept of Gibbs's free energy in Ehrenfest's theory of phase transformation ? Why don't we use Helmholtz free energy concept?
0
votes
1answer
20 views

Making a home made projector bur lens an issur

This got booted out if the lifehacker forum so I'll try here I read a nice tutorial here which tells you how to make a homemade projector for two quid. Lovely thinks I so I trotted down to the local ...
-1
votes
0answers
29 views

Electron-positron annihilation

Consider this problem An electron with kinetic energy K=1Mev collides with a positron at rest. In the collision, both particles mutually annihiliate, creating two gamma rays with equal energy, each ...
1
vote
1answer
36 views

How to start using IDL in 2015?

Unfortunately it looks like I have to run a bit of old astronomy software on IDL. I keep running into statements that "I need to buy a license" in order to run IDL. Is this true? How can I ...
0
votes
0answers
42 views

Is this solvable? Time-dependent perturbation theory

The question is A hydrogen atom is placed in a time-dependent homogeneous electric field given by $$ \varepsilon(t) = \varepsilon_0(t^2 + \tau^2)^{-1} $$ where $\varepsilon_0$ and ...
0
votes
0answers
8 views

Can I use an IV curve alone to differentiate between metallic, semiconducting and insulating materials?

Assuming the size of the bandgap is expressed as resistance in the IV curve, could I tell between metals, semiconductors an insulators by only doing an IV sweep? For example very high slopes (large ...

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