0
votes
1answer
16 views

why do magnetic field lines leave the north pole and enter the south pole?

suppose we have a bar magnet |S_______________N| ... we can imagine it to be |S-N-S-N-S-N-S-N| So, why do we see the lines leave the north pole and enter the south pole externally? What ...
0
votes
0answers
4 views

why in a solenoid the magnetic lines resemble to that of a bar magnet?

each loop in the solenoid will have its own magnetic field around it.In that case it wont resemble the magnetic lines formed by a bar magnet...but we see that it is the same...why is it so?
4
votes
4answers
4k views

Reynolds number and inertial force

The Reynolds number is defined as the ratio of ´inertial´ forces to viscous forces. $$ Re = \frac{\text{Inertial Forces}}{\text{Viscous Forces}}$$ Now, viscous forces make sense to me. They are ...
2
votes
2answers
74 views

Physical interpretation of order of tensor indices

Using positional index notation with tensors is common. For example, the following simple equation from Carroll's Spacetime and Geometry text (eq. 3.146): $$ R = R^\mu_{\,\,\mu} = ...
0
votes
1answer
22 views

Confusion about the Definition of Boiling Point

From the description of boiling here: Boiling is the rapid vaporization of a liquid, which occurs when a liquid is heated to its boiling point, the temperature at which the vapor pressure of the ...
2
votes
3answers
135 views

Is thermodynamic free energy and potential energy the same thing?

The equation for free energy $F$ and potential energy $E_{pot}$ are: $$ F=U-TS \\ E_{pot} = E_{tot} -E_{kin} $$ But the temperature $T$ is proportional to the average kinetic energy of a system. So ...
10
votes
2answers
429 views

Small oscillations of heavy string

I'm solving problem in classical field theory and I have some difficulties. I'm trying to study small oscilations of heavy string with fixed points. First of all I wrote down this Lagrangian: ...
-1
votes
0answers
14 views

Can the nonlinear hydrodynamic be ignored in the process of a ship leaning slowly? [on hold]

Can the nonlinear hydrodynamic be ignored in the process of a ship leaning slowly, and the ship capsized ultimately. Thanks!
1
vote
0answers
28 views

Sum of energy from torques of several disks in double rotation

Here the study: 2 Layers of red disks turn at $w_1$ clockwise around green axis (center of the image). All red disks are link together with green stems. All red disks turn at $w_2$ anticlockwise ...
0
votes
1answer
31 views

Alternating Current/Electromototive Force equaling 0?

All alternating current diagrams are drawn as sinusoidal waves that intercept with x axis. Given our usual sine wave that equals to 0 at 180° it would mean the alternating current would equal to 0. If ...
7
votes
1answer
133 views

Third-order susceptibilities of metals?

Can anyone point me to a source for measurements of the third-order nonlinear electric susceptibilities $\chi^{(3)}$ of various metals? Specifically in relation to the AC Kerr effect, so measurements ...
2
votes
3answers
55 views

Solving flow equations with less information

Suppose we consider the flow of a fluid through a channel, considered to happen in a plane. We want to consider the region $D = [0,L]\times [-a,a]\subset \mathbb{R}^2$ representing the piece of the ...
4
votes
1answer
35 views

Imaginary time is to inverse temperature what imaginary entropy is to …?

The Wick-Rotation rotates imaginary time into inverse temperature (as can be seen from its "rotating" the Schrödinger equation into the heat equation). Now since entropy is temperature's conjugate, I ...
1
vote
1answer
56 views

Why is the law of the p-n junction valid under forward bias?

I'm currently studying the physics of the PN junction. I went though the derivation of the built-in potential in the PN junction under equilibrium: $$ {Diffusion\ current\ density} = {Drift\ current\ ...
2
votes
4answers
139 views

Why does a bubble take a spherical shape?

I suspect this has something to do with thermodynamics and the isoperimetric inequality and I'm interested in a mathematical derivation of this result.
0
votes
0answers
45 views

Results from TLE & SGP4 propagation - don't seem right & need help with interpretation [on hold]

I acquired a TLE of the ISS from internet and used the C++ SGP4 propagator to compute future position and velocity vectors of the Station. I am a little unsure about some aspects of results though and ...
15
votes
2answers
461 views

Do neutrinos travel faster than light in air?

I read in wiki that the speed of light is 88km/s slower in air than it is in a vacuum. Do neutrinos travel faster than light in air?
3
votes
0answers
15 views

How can I estimate the density of fog?

I'm working on investigating the effect fog has on drag. I have assumed an air density of $1.225 \frac{\text{kg}}{\text{m}^3}$ for dry air, but I don't know what value for density I could assume that ...
0
votes
1answer
16 views

Negative charge on capacitor, Kirchoff differential equation with step function

I'm solving a differential equation of the form $$200q'+\frac{200}{3}q=3U_o-6U_6+3U_{12}$$ Where $U$ is the Heaviside step function. $q(0)=0 [Coulombs] $ After solving it, I get that at time $t=18$ ...
0
votes
0answers
33 views

Atom in a box and collapse of the wave-function

Suppose I have an atom trapped in an optically transparent box. I'm assuming the atom is bouncing off of the walls and not bonding, i.e. the center of mass of the atom experiences a square well. Now ...
1
vote
1answer
246 views

Electric field from current without Maxwell's law of induction

A long, straight wire carries a current that decreases linearly with time. What is the direction of the induced electric field outside the wire? I would interpret this as follows: a current ...
1
vote
0answers
49 views

Is it fundamentally possible to capture an orthographic image of the real world?

I thought about asking this question of Photography SE, but I decided that this sort of a fundamental physics question regarding light and dimensional observation, so I decided to cross-post it in ...
0
votes
0answers
14 views

What does it mean that quantum teleportation can be classically simulated?

Quoting here from Quantum Computation by Neilsen and Chuang : (Gottesman–Knill theorem) Suppose a quantum computation is performed which involves only the following elements: state preparations ...
0
votes
0answers
16 views

Finding the balance point of a walking stick with a curve (centre of mass) [on hold]

There is a thin walking stick with a straight section of 80cm, and a semicircular handle of diameter 10cm. Let A be the point of the stick which touches the ground (i.e. away from the handle), and B ...
-1
votes
0answers
34 views

How is time real?

Isn't time a human created concept? I mean why hasn't anybody tread on the rationale that there's no time, only physical and chemical reactions which strive to react with each other at a different ...
-1
votes
0answers
15 views

Rotational Inertia of Two rods

In the figure, two particles, each with mass $ = 0.82 \text { kg}$ are fastened to each other, and to a rotation axis at $O$, by two thin rods, each with length $d = 5.3 \text { cm}$ and mass $M = 1.0 ...
3
votes
1answer
108 views

Poles for a particle scattered in a delta potential

I am working on problem a professor gave me to get an idea for the research he does, and have hit a point where I'm having a difficult time seeing where I need to go from where I'm at. I would also ...
2
votes
5answers
413 views

If I replace all my lights with LEDs will my heating costs increase?

A number of nations are passing bills to phase out incandescent light bulbs. The thinking is that the tungsten filament is an inefficient method of turning electricity into light, the rest of the ...
12
votes
5answers
3k views

How fast would someone have to run to travel vertically up a wall?

I am currently doing a physics project on the effects of so-called 'super-speed'.I was wondering how fast you would have to run to vertically travel up a wall? That is, to negate the force of gravity. ...
3
votes
1answer
81 views

Correct tetrad index notation

There seems to be some different conventions on the indexes of the tetrad. I am wondering which is the standard, which is correct, and which is an abuse of notation. In Sean Carroll's notes and in ...
0
votes
1answer
115 views
2
votes
1answer
184 views

Does the low-energy gauge structure depend on the choice of $SU(2)$ gauge freedom?

The starting point and notations used here are presented in Two puzzles on the Projective Symmetry Group(PSG)?. As we know, Invariant Gauge Group(IGG) is a normal subgroup of Projective Symmetry ...
1
vote
0answers
34 views

How to calculate topological charge? [on hold]

For a complex vector field in two dimensions with one or more phase singularity - a point where the field amplitude is zero and the phase is undefined - how do you explicitly calculate the total ...
3
votes
1answer
37 views

Classification of small extra-solar system bodies

A Small Solar System Body (SSSB) is an object in the Solar System that is neither a planet, nor a dwarf planet, nor a satellite. This encompasses all comets and all minor planets, as well as all ...
2
votes
5answers
1k views

Is voltage difference always proportional to its derivative?

We write, because of Ohm's law: $$V=RI(t),$$ but also we have $$C\frac{dV}{dt}=I(t).$$ From the first equation we deduce that $V\propto I$ and from the second $\dot V\propto I$. So we can conclude ...
7
votes
2answers
106 views

Could you theoretically map the internal distribution of mass in a black hole using hawking radiation?

Assuming you could measure the qualities of the radiation emanating from all around a black hole, could this be used to determine the internal geometry or makeup of the mass inside?
11
votes
5answers
982 views

Is a suit that hides a soldier's heat signature fundamentally possible?

I recently played "Crysis", a game where the protagonist wears a suit that allows the player to hide both himself and his heat signature. Then I watched Iron Man 3, where a kid suggests that Tony ...
0
votes
0answers
32 views

About the nature of the electric current

I'm currently studying electricity on my own, and as I read in a metal electrons are moving across the metal freely (depending on the attraction of the nucleus). As we close the circuit, an ...
1
vote
2answers
111 views

Change of quark flavour?

what do they mean by "in a weak interaction, quark flavor can change" I know that in a weak interaction strangeness is conserved... so is this what the statement is referring to.
8
votes
1answer
317 views

Black & Scholes and the Quantum Mechanics

I am interested in the link between the Black & Scholes equation and quantum mechanics. I start from the Black & Scholes PDE $$ \frac{\partial C}{\partial t} = -\frac{1}{2}\sigma^2 S^2 ...
1
vote
0answers
15 views

Has a gas in the process of diffusion a definite phase? What about liquids?

If we have a gas diffusing through say a solid metal, or gas diffusing into a liquid, what phase is the diffusing molecules considered to be in (or is it even possible to define this)? Is it possible ...
-1
votes
0answers
12 views

Setting the peak or peak to peak output voltage [migrated]

Can the peak or peak to peak output voltage of a function generator be set without the aid of auxiliary instrument such as DMM or Oscilloscope?
1
vote
2answers
75 views

Quantum Eraser thought experiment with light photons of distinct color

I tried to recreate the Quantum Eraser experiment into a thought experiment with a few changes. It left me a little perplexed as to what outcomes I should expect. Any help would be appreciated. Lets ...
-6
votes
0answers
38 views

Finding angular accleration [on hold]

Your car tire is rotating at $3.2\,\,\rm rev/s$ when suddenly you press down hard on the accelerator. After traveling $240\,\,\rm m$ , the tire's rotation has increased to $6.2\,\, \rm rev/s$ . The ...
0
votes
5answers
178 views

How to determine “timelike”-ness without using a coordinate system?

It has been stated here that: we can say, without introducing a coordinate system, that the interval associated with two events is timelike, lightlike, or spacelike. This assertion appears at ...
0
votes
0answers
15 views

How does Brake specific fuel consumption vary with Brake mean effective pressure?

I'm aware that there is a certain relationship between brake specific fuel consumption (BSFC) and brake mean effective pressure (BMEP), but I am wondering if someone could explain how each varies with ...
-2
votes
1answer
24 views

energy from nuclear decay prevention [on hold]

A neutron is stable when next to a proton in hydrogen but unstable if two neutrons are present. Could energy be obtained by preventing neutron decay in tritium with a strong magnetic field using Lenz ...
1
vote
2answers
55 views

Percent error calculations dilemma

I have a set of experimental results for calculating g: 9.82 9.52 10.77 10.39 9.75 9.79 10.13 10.56 10.26 9.84 10.07 9.58 These were taken using a pendulum experiment. My dilemma is that, ...
1
vote
1answer
44 views

Can one calculate the distance from Earth to the camera, given a single picture?

Given an image of (part of) a sphere of known size, can one calculate the distance to the camera based on the relative size of the sphere in the image? My instinct is "no" unless you have some fixed ...
2
votes
0answers
17 views

What makes Monocrystalline silicon a good semi-conductor? [on hold]

I'm researching Monocrystalline silicon for a school project and focusing on its application in Electronics. One area I'm researching is why the material is a good semiconductor, and what properties ...

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