1
vote
3answers
333 views

Two bodies of equal mass thrown from a height-Practical physics question

I have a doubt about this question: Two bodies of masses $M$ and $m$ are allowed to fall from the same height. If the air resistance be the same for each of the bodies, will the two bodies reach ...
0
votes
1answer
1k views

why stopping potential in the photoelectric effect is negative?

I am reading an introduction article for photoelectric effect. It is said that the variable potential was tuned until no single one photoelectron can reach the electron collection plate. But if we ...
1
vote
1answer
3k views

Zero divergence of Electric field

I'm trying to rigorously derive the integral form of Gauss's law from Coulomb's law and the divergence theorem. Arrive at $$ \oint\limits_{\partial V} E\cdot da = \begin{cases} \frac q\epsilon_{o}...
0
votes
1answer
69 views

How was phase randomly changing in CHSH test (M. A. Rowe and others)?

Measuring phase of photon should always be random while checking CHSH inequality, but i can't explain this: http://qudev.ethz.ch/content/courses/QSIT08/pdfs/Rowe01.pdf (the most clear experiment i ...
0
votes
0answers
46 views

Bound states and extensive field configurations

What are extensive field configurations in QFT (instantons, monopoles etc.)? What is the difference in description of their contribution in path integral value or in $n$-point operator functions from ...
0
votes
1answer
94 views

trying to understand the electricl potential and potential energy

I am trying to understand some facts on electrical potential and potential energy. It is quite confusing in the text to say that the zero potential could be freely chosen for convenience. In that case,...
0
votes
1answer
131 views

Field and Charge densities in two dimensional corners and along edges

In jackson's book, we can derive the equation as following. $\sigma(\rho)=\epsilon_{0}E_{\phi}(\rho, 0)\approx-\frac{\epsilon\pi a_{1}}{\beta}\rho^{(\pi/\beta)-1}---(2.75)$ My question is there are ...
4
votes
3answers
3k views

Why does the sea horizon line always seems to be at the same height as one's eyes?

I wonder why, when I look at a sea/ocean, the horizon line always seems to be at the same height as my eyes, no matter how many meters I am above the sea level. This is something I noticed when I ...
2
votes
2answers
1k views

Gas viscosity at high pressure, high temperature

EDIT 1 PER COMMENTS I am wanting to model nitrogen gas viscosity as a function of pressure and temperature OR learn of an existing equation that models nitrogen viscosity for the pressure and ...
5
votes
3answers
452 views

Why does the air pressure at the surface of the earth exactly equal the weight of the entire air column above it

Why does the air pressure at the surface of the earth (resulting from collisions of molecules on the surface of the earth which has to do with the velocity of the particles) exactly equal the weight ...
1
vote
0answers
48 views

Pauli's exclusion principle? [duplicate]

What is the idea behind Pauli s exclusion principle? Why should an electron or any particle having non integral spin obey this principle?
-7
votes
3answers
400 views

Where in, Einstein’s “On the Electrodynamics of Moving Bodies” (Relativity), is “Time” reasonably shown to exist, or why is it a valid assumption? [closed]

Given the widespread acceptance that “Einstein’s Relativity” reasonably proves the existence of Space-‘Time’, and thus “Time”... Can any member of the Physics StackExchange please show precisely ...
0
votes
1answer
72 views

Constraints on new unknown stable fermions?

This question is rather speculative, but I would like to ask it anyway. What are the constraints on possibility of discovering new unknown stable fermions of some sort in the future? If I am not ...
1
vote
1answer
47 views

How big are soluted salts in drinking water?

I have just seen the TED talk Michael Pritchard: How to make filthy water drinkable where a device called LifeSaver bottle that filters particles that are bigger than 15nm out of water. I have heard ...
0
votes
1answer
26 views

belts and balls, correct size of holes

I'm working on a robot that has to transport a set of balls up at a 60 degrees angle. In order to do this I want to use a belt system with holes in it. Now my question is how big do these holes have ...
0
votes
1answer
520 views

If the universe is infinite, should there be a duplicate of me with probability 1? [duplicate]

I was just wondering: if the universe is really infinite, and there is a certain probability to find a life form just like me on another planet (for example $1.0 \cdot 10^{-150}$), is it therefore ...
8
votes
2answers
1k views

Does the commutator of anything with itself not vanish?

In a quantum mechanics exam one question was to write the commutator of a couple of operators. Everybody got points taken away since they did not write $[Q_i, Q_i] = 0$ for all the operators $Q_i$ in ...
2
votes
1answer
167 views

Experimental set up of vertical circular motion

We are trying to do the following experiment: http://farside.ph.utexas.edu/teaching/301/lectures/node90.html. At the moment, here is the experimental setup: We have a rod 0.4 m long which rotates ...
2
votes
1answer
435 views

Is the Gibbs-Duhem equation always valid?

The derivation of the Gibbs-Duhem equation from Wikpedia uses: As shown in the Gibbs free energy article, the chemical potential is just another name for the partial molar (or just partial, ...
2
votes
1answer
36 views

$B^{0}$ decay into $K^{+}$ and $K^{-}$: equally probable?

One of the decay modes of the $B^0$ meson is $B^0 \rightarrow K^{*0} \mu^{+}\mu^{-}$, with $K^{*0} \rightarrow K^+ \pi^-$. But because of the $B$-meson oscillatios, we can also have $ B^0 \...
7
votes
2answers
361 views

Is it possible that we have a physical state which is a mixture of discrete eigenstates and continuous ones?

For a system has both continuous and discrete spectrum, is it possible that a physical states is something like: $$\psi(x)=\sum_{n=n_1}^{n=n2}c_n\psi_n(x)+\int_{E_0-\Delta_E}^{E_0+\Delta_E}\psi_E(x)\...
4
votes
0answers
96 views

What is the relation between pseudogap and time reversal symmetry breaking?

Some papers concerning high-$T_c$ superconductor discuss the pseudogap and time reversal symmetry breaking. My questions are: What is the characteristic of order-parameter in pseudogap? How to ...
3
votes
3answers
127 views

Visible light and colors

I recently read an article about quantum chromodynamics which suggested that quarks do not have actually colors because their dimensions are smaller than the wave length of visible light. My question ...
0
votes
1answer
34 views

Why the first Term is higher in energy than the second?

P. W. Atkins writes in his book "MOLECULAR QUANTUM MECHANICS" in section 9.4 "Term symbols and spectral details" "We shall adopt the convention that the first term is higher in energy than the second....
1
vote
0answers
90 views

Optical pumping, Breit-Rabi equation, how to get hyperfine energies?

I'm working on a lab report for a lab on optical pumping using Rb, but I'm seriously struggling with figuring out how to get the hyperfine energies through the Breit-Rabi equation: $$W(F,M)=-\frac{\...
1
vote
1answer
73 views

Help regarding understanding derivation of electrostatic potential in a solution to a problem

I was looking at the solution of finding the energy stored in a charged solid sphere in which the electric field was and then later stated the electrostatic potential is I understand that to ...
1
vote
2answers
264 views

Quick question on free fall of 2 objects [closed]

I am trying to work through a problem, that is basically telling me that two objects were dropped from a building, one was thrown 2 seconds after the previous object, and I have to find out how long ...
1
vote
0answers
60 views

Modeling the creation of transverse waves

Suppose I hang one end of a jump rope against a wall and start waving the other end. I'm interested in knowing the behavior of the jump rope as it starts generating waves. In other words, how can I ...
1
vote
2answers
380 views

What happens when Antimatter interacts with a photon?

So... I was just pondering the energy and particles in the universe. It makes sense that matter is attracted to it's self by a gravitational force - it clumps and forms some kind of gravity ...
1
vote
1answer
403 views

Is shear modulus only applicable to cubical solids?

Do we have any real life/theoretical examples where shear modulus is applicable to non-cubical shapes?
2
votes
1answer
338 views

Thermodynamic Internal Energy Reference States

The internal energy, $U$, of a given thermodynamic state, $\boldsymbol{R}$, as introduced in thermodynamics textbooks like Callen seems to be defined as: $U (\boldsymbol{R}) = \Delta U (\boldsymbol{R}...
2
votes
1answer
162 views

Why does Air Pressure not Matter in Phase Equilibrium?

So long as we are in the ideal gas range, the presence of air does not affect the liquid/solid-vapour equilibrium in any way (such as equilibrium vapour pressure, melting point etc.). Is there a ...
7
votes
1answer
430 views

Kraus operator rank

All quantum operations $\mathcal{E}$ on a system of Hilbert space dimension $\mathcal{d}$ can be generated by an operator-sum representation containing at most $\mathcal{d^2}$ elements. Extending ...
0
votes
2answers
2k views

How do I make an equation to be dimensionally consistent? [closed]

Velocity is related to acceleration and distance by the following expression: $$v^2=2ax^P$$ Find the power P that makes this equation dimensionally consistent. $$\frac{v^2}{2a}=x^P$$ $$P={\log_x ...
2
votes
2answers
31 views

A hypothetical question on mechanics

Being located in a tropical region, I am quite acquainted with the Ceiling fan. I have a question about it. If the top, that is, the axle (I'm not sure of the terminology: I mean the part which is ...
1
vote
1answer
5k views

Work Done in a Thermodynamic System (Cylinder with Piston) [closed]

Heated Piston A cylinder of cross-sectional area 0.0314m^2, filled with argon (a monatomic ideal gas), is sealed with a piston of mass M=25kg that is free to move up and down. The piston is ...
2
votes
1answer
430 views

Expectation value of $a_i^\dagger a_i$ for thermal density matrix

Suppose we have some heat bath with Hamiltonian, $$H=\sum_n \left(a^{\dagger}_na_n+\frac{1}{2}\right)\hbar\omega_n$$ and a density matrix $\rho=Z\exp(-\beta H)$ for some normalisation $Z$. ...
15
votes
1answer
537 views

A Theorem Due to Hodge: Hawking/Ellis

This is probably quite an obscure question but hopefully somebody has a simple answer. I'm studying the proof of the topology theorem on black holes due to Hawking and Ellis (Proposition 9.3.2, p. 335 ...
0
votes
2answers
670 views

Equivalent formulas for electric current density

I am reading an article that states that the "ratio of current to the area for a given surface is known as current density" and is defined as $J = \frac{I}{A}$ where $I$ is the current and $A$ is ...
0
votes
2answers
122 views

Superconducting electromagnets?

Is it true that superconducting electromagnets don't need any power? So... energy to created a magnetic field via a superconductor would be zero? Since resistance is zero, does that also mean that ...
1
vote
2answers
1k views

How did Newton discover the universal law of gravitation?

I am having trouble comprehending how anyone could come up with this formula: $$F = \frac{GMm}{d^2}.$$ Could someone walk me through this?
1
vote
0answers
95 views

Does a superconductor spinning in a magnetic field radiate?

According to the cyclotron radiation formula: $$ \frac{dE}{dt} = - \frac{\sigma_t B^2 V^2}{c \mu_0 }$$ charges will radiate even when moving perpendicular to the magnetic field (which presumably ...
-4
votes
1answer
250 views

How to find Area given Diameter [closed]

I need to convert diamter to area. I have (1/2)'' diamter acting on a steel cable. I need to calculate the stress, which is: o- = Force/Area The Force we know to be: F = 1000 lbs (pounds). Perhaps, ...
0
votes
2answers
43 views

Explain the concept of “accumulated momentum” for an electron

I need someone to help me understand this equation: $ \Delta p = qEt$ where $q$ is the charge, $E$ is the electric field and $t$ is in seconds. I thought that we were supposed to write momentum in ...
1
vote
1answer
65 views

Intensity of Sound Wave

Is the intensity of a sound wave same at all the points through which the wave travels? The formula for intensity is $ I = \frac{{p_0}^2 }{2 \rho v}$. But this does not make sense to me. Shouldn't the ...
3
votes
2answers
120 views

Does turning a light off save electricity in a room heated by an electric space heater?

Suppose I've got a basement that kept heated to 20 degrees Celsius using an electric space heater with thermostat. There are no windows in this basement (light is not escaping the room in any ...
3
votes
1answer
89 views

Why was the asteroid 101955 Bennu chosen by the NASA OSIRIS-REx sample return mission?

Please explain it in simple terms. Why was THIS asteroid chosen among all the thousand of asteroids?
2
votes
1answer
139 views

Why is plasma confinement on the NIF called inertial confinement when it appears to be confined by pressure?

I've heard that unlike Tokamaks that use magnetic confinement of the plasma, the NIF project uses 'inertial' confinement. What's inertial about it? Do they spin the plasma to use angular momentum like ...
2
votes
1answer
273 views

Avoid dependent equations when applying Kirchoff's Laws

I tutor college students in Physics. In particular, we are currently working on solving circuits using Kirchoff's Laws. In a recent problem, I ended up with a system of linearly dependent equations ...
0
votes
1answer
1k views

Frictionless Cart on a Ramp (Experimental Design Question)

Question: Why is the calculated value for our final velocity higher than our predicted value? Since our prediction neglected air resistance and friction, shouldn't the velocity for the actual cart ...

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