"when charge flows over a surface, we describe it by the surface current density, K. Consider a 'ribbon' of infinitesimal width dL running parallel to the current flow. If the...

Surface current density-logic and definition contradict!]]>

1. Janus

2. Marzena...

VOTE PF Photo Contest - That's Odd!]]>

How to remove Ethanol from Gasoline?]]>

Solving a definite integral by differentiation under the int]]>

(a)

A spaceship at rest in a certain reference frame S is given a speed increment of 0.50c. Relative to its new frame, it is then given a further 0.50c increment.This process is continued until its speed with respect to its...

special relativity and particle accelerator]]>

From ##\mathbb{Z}_3## to ##\mathbb{Z}_{15}##

I know how to do this if we assumed that the rings had to be unital. In that case, there can be no non-trivial...

Is there an injective ring homomorphism?]]>

Another Newbie]]>

Hi everybody! I have trouble understanding the following problem, hopefully somebody can help!

Show that the electrostatic potential

##\phi(\vec{x}) = \phi_\text{free} (\vec{x}) + \phi_\text{ind} (\vec{x}) = \frac{1}{4 \pi...

Verifying a macroscopic Maxwell equation]]>

The box's measurements are 277*120*195mm.

The lamp's power is 15W.

Trying to figure out how long it will take to heat the box so that it reaches a given temperature.

According to Wikipedia ρ

Heating the inside of a box thanks to a lamp]]>

Let ##B_1 = {\begin{bmatrix} 1 \\ 1 \\ 1\\ 0 \end{bmatrix}}, {\begin{bmatrix} 1 \\ 1 \\ 0\\ 0 \end{bmatrix}}, {\begin{bmatrix} 0 \\ 0 \\ 1\\ 1 \end{bmatrix}} ## and ##B_2 = {\begin{bmatrix} 1 \\ 1 \\ 1\\ 1 \end{bmatrix}},...

Finding the transition matrix]]>

Fake News and Science Reporting

...

Fake News and Science Reporting - Comments]]>

What would an antimatter engine be like?]]>

Keep It Simple, Stupid]]>

https://ldtopology.wordpress.com/2017/03/18/a-new-mathematicians-apology/]]>

A single-turn wire loop produces a magnetic field of 41.2 μT at its center, and 5.15 nT on its axis, at 20.0 cm from the loop center.

Find loop raidus and current.

F = qv x B

Find loop radius and current via magnetic field?]]>

If you know any, please advise.

Thanks,

Robert]]>

appeared that presents a classical analogue of quantum contextuality. I hope it can help to make...

Classical analogue of quantum contextuality]]>

Thanks,

Priscilla]]>

I hope this is the right place to post this. I'm looking for recommendations for a modeling/drafting cad program that is relatively affordable and capable. I have extensive experience with NX and Solidworks, but can't justify paying for either of those to simply use at home. My non-work...

Recommendations for an affordable 3D CAD for home use]]>

For instance are the RH neutrinos in the vMSM HNL?

Are the RH neutrinos in the Left-Right extensions of the standard model HNL?

Thank you]]>

The bottom of the boat has dimensions a = 50 m, b = 10 m, the height of the ship is c = 5m. Impact created in the bottom a circular hole with a diameter d = 20 mm. The initial height of the upper edge of the ship above the...

Hole in a boat]]>

I'm trying to integrate a signal received on an oscilliscope, but I'm afraid using the function cumtrapz is not giving me the correct value. Here is what I'm seeing when testing out sine functions View attachment 114923

I could apply an FFt to obtain the components and the phases,...

Filter out constant of integration?]]>

In an enclosed system - of say Methane & water - in which the water column is sufficiently large to have significant pressure and some modest temperature difference due to gravity and geothermal effects, how would one calculate / predict the changing methane concentration (or partial...

Dissolved gas concentration in undersaturated liquid column]]>

Why colonize Mars and not the Moon?]]>

A 'gravity battery' could be created by using an energy source to slowly lift a large weight (using gearing or pulleys), then discharged by lowering the weight to...

Another 'Gravity Battery' Question]]>

from what i know, a= (r¨−rθ˙^2) er + (rθ¨+ 2r˙θ˙) eθ ;

(where er and eθ are unit vectors in the radial direction and the direction of increase of the...

significance of terms of acceleration in polar coordinates]]>

What role should ideologies play in scientific research/studies]]>

An electron has two spin states and a set of energy levels E1,E2,....

By the Fermi-dirac distrbution,the mean number of electrons in energy level Ek is...

A quick question about the Fermi-Dirac distribution]]>

View attachment 114904

(a) : There is no interference. (b) : Interference

And i don't know how to approach (c), (d)

View attachment 114906]]>

If you can put a short description or say why you liked it, that would save me the trouble of reading a plot synopsis on wiki.

Go, go, go!]]>

In a simulation using COMSOL, the ratio of specific heats of both 52NiO-YSZ and YSZ are required as these materials are not included in the software's bibliography.

So, I would like to know the ratio of specific heats (gamma) of 52NiO-YSZ and YSZ.

Thank you.]]>

massi]]>

I have recently realised that I am extremely bad at solving "new" problems related to the topics I am working on. Trying to do any question that deviates slightly from the norm will cause me to be stuck on that problem for hours, usually to no...

Bad Problem-Solving Habits]]>

I am trying to modeling financial markets.

Looking for google, I have found this global variable:

long idum

In the main(), it is defined as

idum = -9132434

or in many other ways.

I am using the following libraries:

#include <stdio.h>

#include <stdlib.h>

#include <math.h>...

Long idum in Modeling Financial Market]]>

The approach I'm currently studying is that by Matthew Schwartz. In his QFT book he first solves the classical KG equation...

Understanding the scalar field quantization]]>

This is a follow up question of this thread:

(https://www.physicsforums.com/threads/confused-between-physics-and-computer-science.884599/page-3)

I have always been interested in Physics since high school but I found first year undergraduate Physics very boring and I think I...

A taste of Physics and Computer Science]]>

I am wondering if the function below is Integrable:

$$\frac{\exp{(-\frac{1}{2}(u-2)^2-2u^2)}}{u-2}$$

When I work it out on computer, the integral is finite from -Inf to Inf. But clearly it has a pole at u=2. Is this pole integrable? If yes, what kind of coordinate transform is...

Non-Integrable Function]]>

Using Sturm-Liouville theory, estimate the lowest eigenvalue ##\lambda_0## of...

[tex]

\frac{d^2y}{dx^2}+\lambda xy = 0

[/tex]

With the boundary conditions, ##y(0)=y(\pi)=0##

And explain why your estimate but be strictly...

Sturm-Liouville Eigenvalue Problem (Variational Method?)]]>

I posted this thread hoping that there are experts about quantum physics here. Please if you do not know a lot about the subject, don't answer this question:

First things first, to be clear: I’m NOT building a quantum suicide machine and I’m NOT trying to kill myself. I’m just curious...

How do you build a quantum suicide machine?]]>

Δp=mΔv+vΔm, Δm=0

Δp=mΔv

Therefore, Δp/Δt=mΔv/Δt=ma.

And if I multiply 'r' to both sides

rF=rma, which is τ=rma

My question is: is 'a' centripetal acceleration or is it tangential acceleration?

If 'a' is centripetal acceleration, which is v^2/r, τ=rmv^2/r=mv^2?

Also I don't...

τ=mv^2 ? (Torque question)]]>

This is my calculation..Am I on the right...

Force to stop a person on a treadmill]]>

1) In order for a solution to count, a full derivation or proof must be given. Answers with no proof will be ignored.

2) It is fine to use nontrivial results without proof as long as you cite them and as long as it is "common...

Math Challenge by Erland #2]]>

What about a situation when we have a sphere whose radius is R, and it's half full with...

Water pressure in a sphere]]>

Beam-powered propulsion - keeping the beam focused]]>

Hello,

I know about the inertia tensor about one axis, but how about a body that rotates around 3 axis x,y and z such as a spacecraft with changes in the attitude.

Thanks for you help.

Inertia tensor of a body rotating about 3 axes]]>

I am investigating a scenario where a pendulum with a bob attached is released from an angle and pushes a box to a certain distance. My goal is to find the coefficient of friction between the box and the surface it moved on.

I...

Finding the coefficient of friction]]>

Q1

Resistance at 0 degrees Celsius = 3840 ohms

Resistance at 100 degrees Celsius = 190 ohms

Resistance at ? degrees Celsius = 2300 ohms

a. Calculate the temperature of the water according to calibrated thermistor assuming the...

Thermodynamics and thermometers (Thermistor)]]>

Can arXiv papers be considered as reliable sources of information?]]>

I've been reading up on EM waves and I feel I'm slowly starting to get it, but I'm not entirely sure if I do, so I was wondering if anyone could help so I can be sure I'm not making some false conclusions here. I can't seem to find any answers to the less certain parts here

So as I...

Questions about light waves]]>

Show that the rings ##2 \mathbb{Z}## and ##3 \mathbb{Z}## are not isomorphic.

I know how to show that two structures are isomorphic: find an isomorphism....

Show that two rings are not isomorphic]]>

Clock synchronization]]>

My main interests are Relativity and Quantum Theory. Currently trying to get my head around Maths for relativity.

I am also interested in learning Science...

Hi! From a new member]]>

Neutral vector mesons with ##J^{PC} = 1^{−−}## include the ##\phi## (mφ = 1020 MeV), ##J/\psi## (mJ/ψ = 3100 MeV), and ##\Upsilon## (mΥ = 9460 MeV), with quark content ss¯, cc¯, and b ¯b respectively. The decays of these...

Decay Widths of Neutral Vector Mesons]]>

Magnitude-5.3 earthquake hits Japan's Fukushima

http://www.usatoday.com/story/news/world/2013/09/19/japan-fukushima-nuclear-plant/2835493/

but!

after that, the sound waves form a cone... what is that? is that the head of each wave being produced behind the previous wave and then blasting...

What do the sound waves look like after Mach 1?]]>

Why does formation of snow flakes not violate entropy law?]]>

I have a question regarding the construction of solutions to the Diracequation for generell [itex] \vec{p} [/itex]. In my lecturenotes (and also in Itzykson/Zuber) it is stated that it is easier than boosting the restframe-solutions, to construct them by using [tex]...

Solution to the Dirac equation]]>

Circuit Board Design]]>

A classmate says "Since there are 2n^2 electrons possible in each energy level, and the atom with the greatest number of electrons has 118 electrons, that must mean that u is the highest possible value for n, because a value of...

Grade 12 chemistry homework help -- 2n^2 electrons possible in each energy level]]>

I have a question that came up to my mind while thinking about the evolution of our universe and quantum mechanics. It involves cosmology so maybe that was the right spot to post it, and of course the moderators can do it if they feel it's more adequate for the thread, but my...

Many worlds and cosmological evolution]]>

Write the density operator

$$\rho=\frac{1}{3}|u><u|+\frac{2}{3}|v><v|+\frac{\sqrt{2}}{3}(|u><v|+|v><u|, \quad where <u|v>=0$$

In matrix form

$$\rho=\sum_i p_i |\psi><\psi|$$

Density Operator to Matrix Form]]>

Many Worlds Interpretations and probabilities]]>

How many methods to cause an electron to radiate?]]>

I have carried out an experiment on 2 hoses. Hose A, a typical garden hose of 15mm OD 10mm ID and hose B a polyester woven lay flat fire type hose of 52mm OD 49mm ID. When inflated to 4 bar pressure hose A didn't straighten and was only seen to bulge in the circumferential direction,...

Deflection of hose when internally pressurised]]>

question about observation]]>

Preferably in an if.... then..... because...... statement.]]>

A wooden box is painted completely with black paint. The interior dimensions are 18”x24”x3.5”. The bottom and sides are made with 9 pieces of 2x4 douglas-fir-larch dimension wood lumber. The top of the box is open and is covered...

Thermal Radiation]]>

Deriving functions relating to condition numbers]]>

I know that ∑n=1 to infinity (sin(p/n)) diverges due using comparison test with pi/n, despite it approaching 0 as n approaches infinity.

However, an alternating series with (-1)^n*sin(pi/n) converges. Which does not make sense...

Why does (-1)^n(sin(pi/n)) converge when (sin(p/n)) diverges]]>

I'm using James Stewart Calculus 8th edition. I love the book, but the lack of the student solution book. I bought it and is a great source. The problem I'm having is that some problems are simplified so much and they skip steps, which for me it frustrates me. I was wondering if there...

Another math resource that can help me?]]>

For now, it seems that the forces exerted on the block are balanced - thus it doesn't accelerate.

The forces exerted on the floor are, however, not balanced. The floor is not accelerating downwards, I must then...

A block on the floor - forces]]>

This is Exercise 19.1 in MTW - See attachment

See attachment

I've worked through 19.3a, 19.3b and 19.3c ( see post by zn5252 back in March 2013 replied to by...

Metric outside a weakly gravitating body (MTW Ex 19.1)]]>

So I've decided to try and make a copper wire magnet generator (real small) for part of my senior design project. If I can get this to work I can potentially reduce my fixture significantly. Anyways, I purchased some real small wind turbine generators off the shelf to play with...

Magnet Wire Generator]]>

I'm confused as to how this is able to receive a differential voltage of +/- from a single power supply. (Yes, I know the picture says dual power supply.)

Normally I have to short the negative to ground on one side of a dual power supply, and short the positive...

Eval op amp achieves +/- power from single power supply?]]>

The intial step in the digestion of milk in Humans is carried out by which of the following enzymes?

A) lipase B) trypsin C) rennin (No, not renin) D) pepsin

Casein is converted to Paracasein by...

Digestion of milk in humans]]>

My question is how are the coils "charged"? How do we...

How are Superconducting Coils charged?]]>

It seems to...

How Energy Is Spread In An Electric Kiln]]>

https://www.quantamagazine.org/20150428-how-quantum-pairs-stitch-space-time/]]>

During transcription processes, which molecule in genes is "first in line", the phosphate group or the ribose sugar? I know they line up interchangeably, but does one of them "start" the process first?

I guess I could ask the same thing about proteins...

Order of molecules during transcription]]>

Light and the nature of space]]>

Is it too late to study physics at the age of 38?]]>

What does the magnetic moment of a particle depend on?]]>

$$\frac{\partial u}{\partial t} + x^2 + t+\left(\frac{\partial u}{\partial x}\right)^2 = 0\\

u(x,0)=0$$

$$

\dot{x} = 2 u_x ;\,\,t=0,\,\,x=\xi\\

\dot{u}=2(u_x)^2+u_t...

Method of Characteristics]]>

@Greg Bernhardt : Is PhysicsForums...

March For Science, April 22, 2017]]>

(This is more of a math question but I thought Astronomy people would be more familiar with the equation and how it's used)

So in Monaghan 1992 (http://adsabs.harvard.edu/abs/1992ARA&A..30..543M, bottom of pg 554) a cubic spline in three dimensions is defined. I tried to...

How is it that the SPH cubic spline kernel in normalized?]]>

This thread is to post updates in your application process, notably acceptances or waitlists.

I applied to SULI at Argonne; they first opened applications up for staff/group review

SULI DOE Acceptance Thread Summer 2017]]>

Hi there! So I have a problem regarding a particle of mass m moving down an inverted cone under the force of gravity. The cone is linear with equation z(r) = r, in cylindrical coordinates (r, theta, z)

A. Write down the...

Particle moving inside an inverted cone - Lagrangian]]>

Tiny Tweak in Teaching Basic Circuits]]>

The...

Tube Bending Stress]]>

I'm working through chapter 2 of Michael Tinkham's Introduction to Superconductivity. On page 40, he asserts that the skin-depth for a general complex conductivity is (In Gaussian units)

$$\delta = \frac{c}{\sqrt{2\pi\omega\left(|\sigma| + \sigma_2\right)}}$$

where $$\sigma = \sigma_1...

Penetration Depth of General Complex Conductivity]]>

Gauss' gun/magnetic linear accelerator]]>