0
votes
1answer
122 views

Very confused about effective spring constant

I know that for springs in parallel, the effective spring constant is $k_1+k_2$ and for springs in series the constant is $1/(1/k_1+1/k_2)$. But there are some weird problems where finding the ...
0
votes
0answers
8 views
0
votes
0answers
16 views

Flow Rate Calculation from a drain tank through a pipe

I want to know how to calculate the flowrate (Q) of a drain tank flowing through a pipe (see the figure below) All I know is that Q=Velocity(V) x Area (A) V= sqrt(2*g*H)=sqrt(2*9.81*10)=14m/s. I ...
41
votes
7answers
5k views

Why don't two musical instruments sometimes generate destructive interference?

I'm an electrical engineer, and I understand wave propagation, interference patterns, and so on. But I'm missing something basic, so perhaps my understanding isn't as good as I believe. I'll show my ...
0
votes
1answer
13 views

How to check if some term in the Lagrangian involving gauge bosons is gauge invariant without explicit computations?

Normally (for fermions and scalars) we can simply use the decomposition of tensor products of gauge group representations to find invariant terms that we can write into the Lagrangian. For example ...
8
votes
4answers
2k views

Entropy and the principle of least action

Is there any link between the law of maximum entropy and the principle of least action. Is it possible to derive one from the other ?
19
votes
4answers
2k views

Why do atomic clocks only use caesium?

Modern atomic clocks only use caesium atoms as oscillators. Why don't we use other atoms for this role?
0
votes
0answers
15 views

Global cosmic strings evolution

Recently I've read about axion string. It can be shown that the energy per unit length of the string located along $z$ axis is $$ \mu = 2 \pi f_{a}^{2}\ln\left( \frac{L}{\delta}\right), $$ where $L$ ...
0
votes
0answers
20 views

Gauge freedom in tetrad

I asked the question in the MathOverflow, but didn't get any response. I thought maybe better luck here. I'm reading the following paper about Petrov type D space times called "Type D vacuum ...
0
votes
1answer
281 views

Rigid body problem in 2d

I have some questions about this exercise: In an horizontal plane, a $OA$ bar with mass $m$ and length $a$ moves, with another bar $AB$ (same mass, double length) attached in the point A. In the ...
0
votes
0answers
22 views

Doubts taking the second functional derivative of the Klein Gordon action

I have very little background with functional derivatives and I would like to clarify some issues. I am trying to compute the second functional derivative of the Klein Gordon action expressed in real ...
0
votes
1answer
17 views

Do gauge bosons really transform according to the adjoint representation of the gauge group?

Its commonly said that gauge bosons transform according to the adjoint representation of the corresponding gauge group. For example, for $SU(2)$ the gauge bosons live in the adjoint $3$ dimensional ...
0
votes
0answers
17 views

Why are bare mass terms for W-bosons forbidden, but coupling terms to Higgs doublets allowed?

The $W$ bosons live in the adjoint rep of $SU(2)$, which is three dimensional. The standard model Higgs lives in a $SU(2)$ doublet, i.e. the two dimensional rep. The $W$ bosons get their mass ...
8
votes
4answers
3k views
+50

Is quantum entanglement functionally equivalent to a measurement?

I saw the following talk the other day: http://www.youtube.com/watch?v=dEaecUuEqfc&feature=share In it, Dr. Ron Garret posits that entanglement isn't really that "special" of a property. He ...
0
votes
1answer
18 views

How to improve the power output of an AC motor without changing its characteristics

I have an AC motor at 230V/50Hz and 2.2 KW power that will power a drilling bit for cutting wood. The motor has 3000 RPM, but if I attach the drilling bit (8 cm wide, 15 cm long and with a step of 8 ...
-1
votes
0answers
26 views

I tried to solve circuit analysis problem but it failed [on hold]

I tried to solve circuit analysis problem in Hayt's Circuit Analysis 7th. But my answer is wrong and I don't know why I failed to solve this. Here's the question. I have to find what the value of v3 ...
2
votes
0answers
14 views

Spinning rubber ball with equatorial ridge

I have this rubber ball with something like a very slight equatorial ridge (sort of like Saturn's moon Iapetus) which I often spin around on my desk. I keep noticing that no matter the inclination of ...
0
votes
1answer
15 views

Symmetry axis and products of inertia

So if we have an object that has a symmetry axis let us say $z$-axis is a symmetry axis does this mean that the product of inertia $I_{zx} = I_{zy} = 0$? And if that is true why is it true ...
0
votes
1answer
145 views

Difference between directional and omnidirectional transmission or reception?

It is suggested that the next generation wireless technology will be highly directional since this increases the signal gain (MIMO) and decreases interference. How will the receiver still be able to ...
0
votes
1answer
29 views

Does a free electron, one that's not either in an atom or a wire, have an associated wave-function?

Would a free electron, one that's not either in an atom or moving through a wire, but moving through empty space on its own, have an associated wave-function? Or, is an electron described as a ...
0
votes
0answers
13 views

Mass spectrum of field theory

How can I find the mass spectrum of a field theory given a Lagrangian made of a canonical kinetic term and a potential. I mean, I think I have to find the matrix of the quadratical terms in all the ...
-5
votes
0answers
19 views

Free fall motion of a body [on hold]

A ball is projected vertically upwards with an initial velocity of 100m/s. Find the speed of the ball at its maximum height Take g=10metre per second square.
-2
votes
0answers
13 views

Average velocity of a clock [on hold]

The minute hand opf a clock is 4 cm long Find the average velocity of the tip of the minute hand between 11:00 a.m to 11:30a.m and 11:00 a.m to 11:30 p.m
0
votes
0answers
16 views

Shear flow in J section type beam

What does the distribution of shear flow look like in a J section type beam. I'm only interested in a qualitative picture of it. I'm not interested in the calculations themselves. It is the top of the ...
0
votes
0answers
16 views

Fun physics book for high school student [duplicate]

can anyone recommend me a physics book for a highschool student (not these typical school books) a book that will let you think mostly interested in theoretical /quantum physics done with the ...
1
vote
1answer
27 views

Is magnetic reconnection reconciliable with magnetic field lines neither starting nor ending?

According to Maxwell's equations, magnetic fields are divergence-free: $\nabla \cdot \mathbf{B} = 0$. If I understand this correctly, this means that magnetic field lines do not start or end. How can ...
-6
votes
0answers
16 views

Need help please [on hold]

An electron's speed is doubled from $0.2~c$ to $0.4~c$. By what ratio does its momentum increase? What happens to the momentum ratio when the electron's speed is doubled again from $0.4~c$ to $0.8~c$? ...
0
votes
0answers
23 views

Bertrand's Theorem: Perturbative Methods Leading to $1/r^3$ Solution

My professor and I have been working on a proof of Bertrand's Theorem using perturbative methods. We have arrived at a solution yielding 1/r^3, which we had presumed to be an incorrect result. While ...
0
votes
1answer
163 views

Malleability in metals

I am trying to understand malleability in metal as a result of the micro structure. I am focusing on the metals of antiquity (in order of decreased malleability): Gold, Silver, Copper, and Iron. While ...
-2
votes
0answers
17 views

its tricky circuit to given output voltage find without source [on hold]

solve it two quation in that pic,1) find Vout voltage and 2) no source given and find v1,v2,v3.
2
votes
0answers
25 views

Why Electron Does Not Radiate In Bohr Orbits? [duplicate]

Maxwell said that charged particles radiate when are in accelarating motion. I understand that $nλ=2πr$ must be fulfilled in order to create a sinusoidal standing wave and to satisfy the probability ...
0
votes
0answers
15 views

Hyper/parabolic kepler orbits and “mean anomaly”

In an elliptical kepler orbit there is an easy recipe to describe the motion/position of a satellite at time $t$. One just follows the following steps - an important detail for me is that the ...
0
votes
2answers
92 views

Entropy and Gibbs Free Energy

I've been struggling with the notion of entropy and gibbs free energy for almost three days now. Different sources on and off the internet say different things about entropy. Gibbs Free Energy is ...
0
votes
1answer
26 views

Arbitrary acceleration written as centripetal acceleration of approximating circle

Suppose I want to find the acceleration of a projectile given its trajectory, i.e. its space coordinates as functions of time. I have heard that the acceleration can always be written as the ...
1
vote
1answer
36 views

Quantum computing can be done via measurement alone, why is this significant?

I read in the Afterword section of Nielsen and Chuang's book Quantum Computation and Quantum Information that A second area of progress has been in understanding of what physical resources are ...
0
votes
0answers
8 views

Superconductor in a parallel vs perpendicular field

My question concern's the huge difference in critical fields regarding a thin superconductor(SC) which is surrounded by a magnetic field. lets imagine the SC is a thin film in the x-y Plane: Applying ...
3
votes
1answer
164 views

Hartree-Fock correction to $e$-$e$ interaction

The corrections to the energy per electron in a jellium model (uniform distribution of positive ion charge approximation to the regulated long range order ionic array) is given by (in units of Ry) ...
0
votes
1answer
31 views

Deriving Gravitational Potential Energy using Vectors

Here is my attempt at derivation: First you must find a vector function for the gravitational force. By the inverse square law, the magnitude of gravitational force between two bodies of mass $m$ ...
2
votes
2answers
38 views

Is it possible to go from the Master Equation formalism to Heisenberg-Langevin equations

If I have derived a master equation (e.g. in the Lindblad form) and solved for the density matrix, $\rho(t)$ I can get the mean value of an operator, A as: $ <A> = \mathrm{Tr}A\rho $. But ...
1
vote
1answer
91 views

How to visualize a Schrödinger cat state?

I recently read about Schrödinger cat states (SCS), which are basically a superposition of two coherent states $|\alpha\rangle$ with opposite phases, that is, $$ |cat\rangle = |\alpha\rangle \pm ...
1
vote
1answer
21 views

Preventing Heat Escape

Is is possible to completely prevent heat from escaping from a closed container? Here is a diagram of vacuum flask, which tries to implement the design - Vacuum Flask prevents heat from escaping ...
1
vote
1answer
20 views

Hot water from a faucet

Why does hot water come out of a faucet cloudy white? The cold water comes out clear, but if you turn the hot water tap on, it'll be clear until it gets hot and then turns a cloudy white colour. ...
0
votes
1answer
20 views

Why is voltage essential in circuits?

I understand what voltage is, but why is it necessary for an electric circuit to function? Why can't current flow without a voltage? Thanks
0
votes
2answers
21 views

Velocity of Rocket Exhaust

i recently learned a bit of rocket propulsion.It wasn't much complex but was explained in simple terms.The only problem i had understanding it was that in calculating the thrust of rocket the velocity ...
1
vote
2answers
67 views

Total number of photons per unit volume in a box (extremely confusing)

This is a worked example from a text. a) Find an expression for the number of photons per unit volume with energies between $E$ and $E+dE$ in a cavity at temperature $T$. $$n(E)dE = g(E)f(E)dE = ...
5
votes
0answers
26 views

Reaction of uranium and neutrons emits neutrons, or is it photons?

So we had this test in nuclears physics today, and part of one of the quesitons was the following: When $\rm U^{235}_{92}$ nuclides are bombarded with one neutron, they can decompose to krypton ...
0
votes
0answers
10 views

Modelling Fourier Transform Profilometry

Basically I want to simulate a surface profilometry technique through Matlab. For that I want to create a GUI with controls for generating a grating pattern of light at a particular angle with respect ...
0
votes
1answer
33 views

Heat equation with heat loss to surroundings

I am trying to model one dimensional heat diffusion within a uniform copper rod with insulated ends. In addition, I am including a term that models the heat loss to the surroundings from the lateral ...
0
votes
1answer
119 views

Plane curve transform to moving inertial system coordinates

As a non-phycisist I hope my question makes sense and is understandable. It deals with special relativity. I suppose there is a e.g. plane curve ( e.g. a circle ) given in the x-y plane of of an ...
-2
votes
0answers
18 views

Motion of particle in $T$ seconds [on hold]

A particle starts moving from rest position ($v = 0$) under a constant acceleration $a$. If it travels a distance $\Delta{x}$ in time $T$, what distance will it travel in the next time $T$?

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