0
votes
0answers
2 views

Determinant of block matrix with off diagonals as vectors

I've been given an $(n+1)\times(n+1)$ square matrix, which is written in the form of a block matrix with the following dimensions $ \begin{bmatrix} (1x1) & (nx1)\\ (nx1) & ...
1
vote
1answer
74 views

Entropy of the cosmological constant and the laws of thermodynamics?

Convention The convention being used is: $ A_{C} = $ The classical variable Premise Consider the following toy-model universe: A universe with a positive cosmological constant. Basic ...
0
votes
0answers
3 views

Angular Momentum Addition in Phase Space QM

In my very limited understanding of geometric quantization, we quantize spin by choosing as our phase space $S^2$ with a suitably normalized area form as the symplectic form. Depending on the ...
0
votes
2answers
526 views

Tension in string and gravitational force on bob relative strength

When calculating time period of simple pendulum (an approximation of SHM at small amplitudes) we take gravitational force greater than tension in string and resolve gravitational force in two ...
0
votes
0answers
2 views

Can the internal energy of an ideal gas system increase as temperature decreases?

If change in $\Delta U = Q + W $ Then adding $x$ moles of an ideal gas of lower temperature into a system of internal energy $U$ would increase $U$ as the kinetic energies of the molecules of the ...
0
votes
0answers
5 views

Why is there not always a force in the direction of motion?

This was a question on a physics competition. A girl throws a teddy bear straight up. Consider the motion of the bear only after it has left the girl’s hand but before it touches the ground, and ...
0
votes
2answers
44 views

Cherenkov radiation can it happen in a jar using tap water with 8 thorium laced lantern mantles as a radiation source

I placed 10 thorium laced lantern mantles into a wide mouth glass jar 5.25 inches diameter x 6 inches tall, filled with tap water to just below the threaded neck portion of the jar. The jar mouth ...
0
votes
0answers
11 views

$dU = \sum E_i dp_i + \sum dE_i p_i = TdS - PdV \implies \sum dE_i p_i = - PdV$?

This is a formula my professor gave in class, but I'm entirely lost how he arrived at the conclusion (I understand the assumption). Could anyone help me?
0
votes
1answer
9 views

How is electric field effected by loss of energy of charge?

Recently, I asked a question related to energy of a charge(This is the question). In one of the answers, in the comments section, I got an answer that the strength of the electric field is lessened ...
2
votes
2answers
29 views

Understanding parallel plate capacitors

I need help with understanding this assignment. I originally though of using the equation of Eo*A/D = Q/ΔV but I don't know how to answer this without actual numbers to plug in besides the epsilon-not ...
4
votes
3answers
2k views

What is the meaning of Boltzmann definition of Entropy?

I would like to ask if someone knows the physical meaning of Boltzmann's definition of entropy. of course the formula is pretty straightforward $$S=K_b\ln(Ω)$$ but what in the heck is the natural ...
0
votes
0answers
19 views

Temperature change in Adiabatic stretching of liquid film

The first law applied to a liquid film is $dU = dQ +2\sigma dA$ where $\sigma$ stands for surface tension. Or $dQ = dU + (-2\sigma) dA \leftrightarrow dQ = dU + PdV$ Now suppose we wish to find ...
0
votes
1answer
11 views

Rutherford scattering: question about impact parameter

http://wonka.physics.ncsu.edu/~blondin/py203/HW5solns.pdf I have a question about the solution to a problem I found online. I don't understand why the author plugs in $\theta=90$ when the question is ...
0
votes
0answers
6 views

Dielectric Constant and Frequency

How dielectric constant of a parallel plate capacitor varies by varying frequency in physical terms?
1
vote
2answers
22 views

Intuitive explanation of $1/2(at^2)$ motion equation?

The full equation $$ Xf = X_o + V_o t + \frac{at^2}{2} $$ is integrated from the velocity function (which was integrated from constant acceleration function), right? The problem is, I can't seem to ...
3
votes
1answer
216 views

Quantizing highly nonlinear field-theories?

I'm wondering how to go about quantizing a classical field theory which looks nothing like a free field theory plus a perturbation term. Suppose for concreteness I have the classical hamiltonian $ ...
4
votes
2answers
93 views

The naive idea of the big bang

Many people think that according to big bang cosmology, first there was empty space, then there was an explosion in the middle of the emptiness, and now all the galaxies are flying away from that ...
0
votes
2answers
27 views

Magnetic induction to generate EM waves

Let's say that I create a time varying magnetic field. This field then cuts a conducting circular loop normally. The loop has two protruding wires. Will the protruding wires emit EM waves? I ...
0
votes
4answers
90 views

Quantum entanglement - problem with Bell's inequality

To ask the question, I will state the scenario first. Please let me know if the scenario is not described appropriately. The question is in the scenario itself. There are many questions marks in this ...
0
votes
0answers
8 views

Coulombs Law on Quarks

As I know Quarks have fractional charge ,For this question lets take 2 Strange quarks(A and B) i.e charge of a quark is -1/3. As the Coulombs law states Force On A by B = Kq(A)q(B)/r^2 So F(ab) = ...
2
votes
1answer
330 views

Ladder Operator killing state

So in my last question, @joshphysics showed me how to prove $K_\pm$ were ladder operators. Now I need to show that there is a lowest state, i.e $$\langle m_0|K_+=K_-|m_0\rangle=0$$ I am not ...
0
votes
1answer
9 views

Motivation for integrals over scalar field

I'm looking for good examples of physical motivation for integrals over scalar field. Here is an example I've seen: If you want to know the final temperature of an object that travels through a ...
1
vote
1answer
44 views

Why do some substances undergo sublimation while others do not?

This question is indeed lengthy...but please go through the question at least. From the study of kinetic theory I know that for intuitive answers we can associate the states (liquid, solid,gas) with ...
0
votes
1answer
31 views

To which type of particles gauginos are supposed to couple?

I wonder about to which type of particles gauginos couple in general. I admit my knowledge in supersymmetry is very limited. Let's take an example: The photino. If it behaved similar to the photon, it ...
0
votes
1answer
35 views

CFT and temperature

I have tried to think about this for some time but could not really go anywhere. Sorry for the sloppy question and thanks for any pointer. My question is about CFT at finite temperature and ...
2
votes
4answers
1k views

Proof of Liouville's theorem: Relation between phase space volume and probability distribution function

I understand the proof of Liouville's theorem to the point where we conclude that Hamiltonian flow in phase-space is volume preserving as we flow in the phase space. Meaning the total derivative of ...
0
votes
2answers
37 views

Mass, velocity and momentum

I am trying to figure out a Pinewood Derby Car and ways to make it better while remaining legal. I am a Den Leader, so am racing against other Den Leaders - so if I am DQ'd c'est la vie. Question: ...
1
vote
3answers
48 views

Voltage of a battery in a circuit with an infinite resistance

I have a dilemma that I would like to share with you concerning batteries (without neglecting internal resistance), emf and resistance of a circuit. To better visualize my question you may need to ...
2
votes
2answers
113 views

How to find the direction of an eddy current?

Suppose there is a magnetic field going from left to right. Suppose a thin sheet of metal conductor (e.g. a 1m*1m square) is dropped through the magnetic field such that the plane of the conductor is ...
0
votes
0answers
16 views

Exponential Approximation of the Fermi Function

When $E-E_{F}>>kT$, the Fermi function $f(E)$ may be approximated by an exponential function. Similarly, when $E_{f}-E>>kT$, $1 - f(E)$ may be approximated by an exponential function. ...
0
votes
0answers
9 views

Does ergodic hypothesis depend on the volume constraint of the macrostate or it only concerns with the energy constraint of the macrostate?

Ergodic hypothesis says that: [...] ergodic hypothesis says that, over long periods of time, the time spent by a system in some region of the phase space of microstates with the same energy is ...
-2
votes
1answer
16 views

Vectors finding direction include the difference between “north of east” and “east of north”

In what direction is your friend from the starting point after skiing 3 km east and then 1.5 km north? so far I know that angle= tan-1(opp/adj)=(1.5/3.0) angle= ...
0
votes
4answers
51 views

Can we obtain interference pattern with single electron/photon in Young's double slit experiment? [duplicate]

Can we obtain interference pattern by using single electron/photon in Young's Double slit experiment? If yes, then how ...and if no, then why?
0
votes
1answer
195 views

Inclined plane, circular motion and the friction

Suppose we have a cylinder on an inclined plane of mass $m$ and radius $R$ moving without sliding (so that $\varepsilon = a/R$). Why is the friction $F$ causing the circular motion sometimes lower ...
6
votes
3answers
605 views

Why doesn't hydrostatic pressure glue objects to the seafloor?

Consider a cement block of the same density as sea-water resting on the (perfectly polished) seafloor. I also assume the side-faces of the cement block are highly polished, so that no vertical ...
0
votes
0answers
4 views

what is the relation between heat capacity and mixing ratio

I am supposed to derive an expression for the specific heat capacity $c_p$ for air with a water vapour mass mixing ratio of $\mu$. The hint is: (Use the fact that $c_p= (\frac{\partial H}{\partial ...
1
vote
1answer
20 views

Scattering amplitude Green's function integral

On page 208 of Weinberg's QM book, he calculates the following integral \begin{align} G_k (\vec{x}-\vec{y}) =& \int \frac{d^3 q}{(2\pi \hbar)^3} \frac{e^{i\vec{q} \cdot (\vec{x}-\vec{y})}} ...
0
votes
1answer
11 views

How to calculate power necessary generated from wind turbine to run a motor

I was making a small/cheap wind turbine, and I am stuck on how to calculate the power needed (speed of wind) to run a brushed motor (since I figured that would be the easiest to run with rotor blades ...
1
vote
1answer
332 views

Magnitude of the average velocity vector (not the average speed)

Thank you ahead of time for taking to look at this. For this following problem we were given an answer however I am almost positive the given answer is wrong. It doesn't even make sense. So here is ...
4
votes
1answer
2k views

Good books on elasticity

Can someone suggest good books/textbooks/treatises/etc on elasticity?
0
votes
0answers
16 views

A block floating on water is pushed inside until it touches the bottom. Will the block come back? [duplicate]

A block floating on water contained in a vessel is pushed inside until it touches the bottom of the vessel and then released. Will the block come back? Bouyant force acts because the pressure on ...
0
votes
0answers
25 views

Sign of Wick rotation

Suppose you have the integral $$i \int^\infty_{-\infty} L_M(t) dt$$ and that $L_M$ contains two poles: when $t>0$ the pole lies above the t-axis and when $t<0$ the poles lies below the t-axis. ...
-1
votes
1answer
32 views

Time Dilation and the direct opposite

// I just looked this up in google 30 kilometers per second Thus, the surface of the earth at the equator moves at a speed of 460 meters per second--or roughly 1,000 miles per hour. As ...
-4
votes
0answers
38 views

Could Dark Matter Exist Prior to the Big Bang? [on hold]

Recent discoveries that the universe is accelerating in its expansion has made me consider the possibility that dark matter might have existed prior to the time the universe sprang into existence, ...
-3
votes
0answers
33 views

Optical signals and the electromagnetic spectrum

Are Optical signals are not considered part of the E-M spectrum? Or are they?
0
votes
2answers
249 views

Work and free body diagrams

I am a bit confused with how to find work when there is a free body diagram. I am trying to work out this problem, and in it a box is being pulled at a constant speed by a rope at a constant angle ...
0
votes
0answers
25 views

Calculating the data rate for a baud signal

I have been working on these questions for the past few hours. I am working on calculating the data rate of baud signals, where each symbol can take on one of two levels. I wanted to know if I have ...
1
vote
0answers
30 views

Work by Gravity using Tensors

Now I'm familiar with the various methods for deriving work done by gravity, but I noticed a few things about the situation, and wanted to see if I could properly apply a tensor treatment to the ...
1
vote
3answers
51 views

Bending of light

Why does bending of light(diffraction) occur?
0
votes
1answer
28 views

Why does magnetic field and not electric field invert in a reflection? (related to another question)

When you are talking about an elctromagnetic wave that reflects on a surface (for example here), why do you say that the reflected magnetic field inverts and not the electric field? \begin{align} E_+ ...

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