-1
votes
1answer
15 views

Conduction problem [on hold]

A hot reservoir with a temperature of $782 K$ is $0.56 m$ away from a cold reservoir with a temperature of $331 K$. The two reservoirs are insulated from each other except for a rod of brass ($k = 109 ...
0
votes
1answer
26 views

Heat pump solution to pollution

I have invented a process that converts an air conditioner into a heat pump. How many metric tons of carbon equivalent could be eliminated from entering the atmosphere annually if 1.every air ...
0
votes
0answers
24 views

Ryder QFT, Is there an errata sheet?

Just spent the last hour trying to find one, but to now avail. Has anyone ever seen such a thing?
1
vote
0answers
14 views

What causes that the outer electrons of iron have the same spin and creates a dipool?

Iron has the capability of magnetism. The cause of that is that the spins of electrons in the outer shell are the same so they pushes each other away because of Pauli exclusion principle so they are ...
0
votes
5answers
59 views

If “For every action there is an equal and opposite reaction”, why does a gun not injure the shooter's hand?

If "For every action there is an equal and opposite reaction", why does a gun not injure the shooter's hand? Would not the "equal and opposite reaction" of firing a bullet be the kickback the shooter ...
0
votes
0answers
23 views

What is known about the physics of Planckbrane (another brane) in Randall–Sundrum model?

Randall–Sundrum model imagines that our universe is a five-dimensional anti-de Sitter space and the elementary particles except for the graviton are localized on a (3 + 1)-dimensional brane or branes. ...
2
votes
1answer
161 views

What is the angular distance between Ptolemaic perigees of Mercury?

In his excellent treatment of the history of the science of astronomical distances and sizes, Albert van Helden says (p.29) that The complicated [Ptolemaic] model of Mercury has the curious ...
1
vote
0answers
5 views

What are some good books for studying about Carbon Nanotubes?

Ok, so I am trying to computationally model a Carbon Nanotube FET and I need to know a lot about the actual equations and PDEs(Partial Differential Equations) involved while modeling such a material. ...
0
votes
0answers
14 views

Prove for ideal gas temperature being directly proportional to absolute temperature [on hold]

I have some difficulties proving that the ideal gas temperature is directly proportional to absolute temperature defined by the second law of thermodynamics. The ideal gas temp. is defined by the ...
1
vote
1answer
45 views

How does the fundamental assumption of statistical physics make sense?

Consider two systems A and B in thermal contact. System A has $N_A=3$ simple harmonic oscillators and the system B has $N_B=3$ simple harmonic oscillators as well. Each system has a number of energy ...
7
votes
2answers
126 views

In a Monte Carlo NVT simulation How do I determine equilibration

I'm running an NVT (constant number of particles, volume and temperature) Monte Carlo simulation (Metropolis algorithm) of particles in two dimensions interacting via Lennard-Jonse potential ($U = ...
3
votes
2answers
319 views

Why does a propeller suck in air from the front?

A rotating but fixed propeller sucks in air from the front. What is the cause for this acceleration of air particles? Since propeller blades act like rotating wings, my best guess is that the blades ...
1
vote
1answer
42 views

Conservation of energy in quantum mechanics

In Griffiths' book Introduction to quantum mechanics (second edition, page 37) it states: The time-independent Schrödinger equation says $$\hat{H} \psi_{n} = E_{n}\psi_{n}$$ so $$\langle H ...
0
votes
0answers
31 views

Gravitational force between rod and mass $m$

Why do we integrate along the whole length while finding the gravitational force between a object of mass ($m$) and a rod of length $L$ and mass $M\,?$ Can't we simply use $F=\frac{GmM}{r^2} \, ?$
2
votes
0answers
20 views

Why do Cooper pairs not bump into other particles?

I sort of get how they get formed and how it works but why do they not bump into other particles? and do the spins have to do with this?
0
votes
1answer
13 views

Can a piezoelectric material only vibrate at one frequency?

Given a material X with piezoelectric properties which is used in a ultrasonic transducer, what determines the working frequency of said transducer? If hypothetically such a transducer is specified ...
0
votes
1answer
32 views

Is there a limit to the size of black hole?

I have read answer by @John Rennie in regards to the size and density of black hole. In the last sentence he states that super supermassive black hole ...
11
votes
3answers
1k views

Do electrons in an atom always have the same 'direction'?

Perhaps speaking of direction of an electron isn't quite correct. But does QM indicates a kind of way whether all electrons are going e.g. 'clockwise' or not? Of course QM just gives a probability ...
0
votes
1answer
24 views

Energy method to solving equations of motion? Why does this method work and what is it called?

Given the stated system in the photo we are suppose to prove simple harmonic motion when given an initial displacement $x$ I first considered the total energy of the system which we will call $H$ ...
0
votes
2answers
352 views

Horizontal and vertical acceleration of a ball on a slope?

I understand that you resolve the components of the balls weight parallel and perpendicular to the slope in order to calculate the force due to gravity that actually acts down the slope. The ...
0
votes
2answers
30 views

Equivalent spring constant of setup

A mass $M$ is suspended using two springs having spring constant $k_{1}$ & $k_{2}$ with distance from mass as $a$ & $b$ respectively. Find equivalent spring constant of system. So I ...
1
vote
1answer
25 views

If black holes warp space-time infinitely, does that mean space-time goes on infinitely in all directions?

My thoughts are if a black hole warps space-time infinitely then does that mean space-time goes on in all directions infinitely? Maybe (probably) my understanding of space-time is not great, if ...
2
votes
0answers
16 views

Can the permittivity tensor always be diagonalized? Why is it always an ellipsoid?

For an anisotropic medium, permittivity is a symmetric tensor, with elements as $\epsilon_{ij}$ a) How can one be sure that it is diagonalizable, if some elements, say $\epsilon_{xy}$ and ...
0
votes
0answers
28 views

What is conformal symmetry physically?

I'm reading a paper by t'Hooft http://arxiv.org/abs/1410.6675. There is an argument in the paper that I could not understand: "Now that system, described by Maxwell’s equations, does have conformal ...
2
votes
3answers
186 views

What is supposition of equilibrium? How do Rayleigh, Jean know the electromagnetic wave in equilibrium behave?

In a cavity of dimension L, the wave must give zero amplitude at the wall, means wave equation has zero amplitude. Why? Answer from hyperphysics "since a non-zero value would dissipate energy and ...
2
votes
6answers
96 views

When we write that $F = -\nabla V$ , what would happen if we ommit the (-) minus sign

I have had this question for a long time. In classical mechanics, if we choose $\mathbf F = -\mathbf \nabla \, V,$ with the minus sign, we can proof the work - kinetic energy theorem. What are the ...
167
votes
19answers
24k views
+50

Do we know why there is a speed limit in our universe?

This question is about why we have a universal speed limit (the speed of light in vacuum). Is there a more fundamental law that tells us why this is? I'm not asking why the speed limit is equal to ...
2
votes
2answers
27 views

Why did James Chadwick use berryllium to discover neutrons?

In Rutherford's alpha particle scattering experiment he used gold foil because it's malleable and can be drawn into very thin sheet. Why did James Chadwick use Berryllium while discovering neutrons ...
1
vote
2answers
16 views

Speed of Sound using Resonance

The aim of my experiment was to determine the speed of sound using the theory behind resonance; that, when a vertical pipe open at both ends is partially submerged in water, and a tuning fork ...
15
votes
1answer
2k views

Onsager's Regression Hypothesis, Explained and Demonstrated

Onsager's 1931 regression hypothesis asserts that “…the average regression of fluctuations will obey the same laws as the corresponding macroscopic irreversible process". (Here is the links to ...
0
votes
1answer
993 views

What's the difference between binding energy and separation energy?

My understanding of the two was as follows: the binding energy of a nucleus is, classically speaking, the energy needed to put together/take apart that nucleus completely (i.e. a measure of the strong ...
6
votes
1answer
67 views

How can a bowling ball curve in both directions?

There is a popular video on facebook that I just don't understand. A man spins a bowling ball very fast then slightly taps it down the lane. Somehow it does half of a figure eight, curving around two ...
8
votes
6answers
11k views

Compton scattering vs. photoelectric effect

Say a photon hits some atom. What determines whether there will be a photoelectric effect (photon is absorbed, electron is released) or whether there will be a Compton scattering (the photon is ...
1
vote
4answers
236 views

Frequency of Sound Waves

Is the frequency of the echo (resulted from the reflected sound wave) equal to the frequency of the original sound wave?
10
votes
4answers
2k views

Weightlessness in Satellites

The following is written in my textbook as the reason for weightlessness felt in satellites: The gravitational pull is counterbalanced by the centripetal force. This introduces two problems: ...
0
votes
0answers
18 views

Liquid jet in the absence of gravity [on hold]

On earth, we have liquid jets which are falling and accelerating under influence of gravity ( this cause their radius to decrease ) My question is about liquids in the absence of gravity. Can we make ...
8
votes
4answers
179 views
+50

What does electric field of unpolarized light look like when measured?

When we talk about fermions in mixed state, we say that their state can't be described by a wavefunction and just compute all the probabilities using density matrix. That's OK because the ...
0
votes
0answers
10 views

Changing the Density of a liquid while its surface tension is constant

I'm working on Plateau-Rayleigh waves and I want to investigate the effect of density of the liquid on the wavelength of these waves How can I change the density of the liquid while its surface ...
-1
votes
0answers
11 views

Finding the value of E at a point in a 3D field with 2 separate point charges [on hold]

Having some trouble with this question: A charge 30 nC is situated at the point (x, y, z) = (0, 2, 0) and a charge of –30 nC at the point (0, -2, 0) m. Find E at the points: (a) A = (4, 2, 4) m
9
votes
2answers
299 views

What uniquely defines a CFT?

So, I am quite new to CFT (and a as descriptive answer as possible would be appreciated). I want to know what uniquely defines a CFT in 2D and otherwise. Firstly in 2D, What defines a CFT? So I ...
-1
votes
0answers
21 views

How do I find the co-ordinates and speed of this particle on the x-y plane? [on hold]

I got this question from an old physics exam paper. I'm trying to use the kinematics equations to solve this question but the x and y co-ordinates keep confusing me. Here's the question: A particle ...
0
votes
0answers
11 views

When you make materials smaller is there a trend in the manner light is absorbed or reflected?

For instance if you take gold is shines like yellow, but if you make it smaller I've heared that it absorbes more the smaller frequencies. At a size of 100nm a piece of gold will absorb fe more blue ...
0
votes
1answer
10 views

What is a Light Efficient System?

When reading this paper, I encountered this sentence on the sixth page: When used in conjunction with wide-field microscopy, iterative restoration methods are light efficient. This is most ...
4
votes
1answer
217 views

Are magnetic hysteresis losses relevant to alternating currents flowing in a wire?

Say we have an AC in a magnetically lossy material, like iron. Because of iron's relatively high permeability, skin effect will be more pronounced than it is in say, copper, so this iron wire isn't so ...
0
votes
0answers
24 views

General framework of Supersymmetry

Even the people who are skeptical about SUSY are happy with the SUSY searches going on at LHC because they recognize that SUSY's general framework is quite flexible and the search strategy used in ...
0
votes
1answer
32 views

Relation of the cross product of the functions to the cross product of their Fourier spectra

I know that according to the Convolution theorem the Fourier transform of the convolution of two functions $f$ and $g$ is equal to the product of their Fourier spectra: $\mathcal{F}\{f*g\} = ...
0
votes
2answers
326 views

How come the length of a wire does not affects on the circuit current?

Today we started learning about the electromagnetic induction. Out teacher gave us the following explanation: Suppose we have a conduction frame inside a magnetic field $\vec{B}$ going towards the ...
3
votes
0answers
23 views

Exhaust liquefaction in internal combustion engines

Does an internal combustion engine provide enough efficiency to still deliver mechanical power, if it is forced to liquify it's own exhaust gases by compression? If gas containers would be added to ...
1
vote
0answers
17 views

How to arrange a 3d cymatics experiment?

Various researchers have filmed levitating polystyrene using sound waves. If i were to take 3 speakers and attempt to visualize the standing wave fields formed by the three speakers, how would i do ...
1
vote
2answers
107 views

If I double the amount of oxygen molecules, do I double the paramagnetic force?

Oxygen is well known to be paramagnetic. If I take one molecule, $O_2$, and measure its paramagnetic force due to externally applied magnetic field, and then add another molecule near the first ...

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