0
votes
2answers
19 views

What conditions are necessary for Birkeland currents to form?

If charged particles flow through non-magnetised space will they form Birkeland current? Or can such currents only form along existing magnetic field lines? Part of the reason I ask is this: http://...
2
votes
4answers
7k views

Proof of minimum distance between object and image of a convex lens image being 4*focal length

I can prove that the minimum distance between an object and its image, through a convex lens is 4*focal length, if I assume that the distance between the object and the lens is the same as the ...
2
votes
0answers
38 views

Why are topological phases described by modular tensor categories?

After some reading, I have an inuitive idea what topological phases of matter are. But where is the connection to modular tensor categories? Is there fundamental literature where this is covered? ...
-1
votes
0answers
19 views

What is the gravitational field inside a hollow spherical cavity embedded in a solid sphere? [duplicate]

Imagine a solid sphere of radius $R$. From the inside of this sphere we remove a smaller sphere of radius $r$. The sphere can be situated anywhere inside the massive sphere. How does the gravitational ...
2
votes
2answers
75 views

What are the odds of finding an electron a long way from an atom? As in metres away?

Pretty self-explanatory, heard that there is a chance that you might find an electron on the other side of the universe, just wanted to know.
1
vote
1answer
20 views

Why is it misty at such high temperatures as per weather reports?

I am residing in New Delhi (pardon me for any irrelevant data I might include), and I noticed a really interesting thing. It's an average 30 degrees Celsius out here, and yet, most/some weather ...
0
votes
1answer
57 views

Approximation of an integral for time dependent quantum Hamiltonian

I want to approximate $\displaystyle\int_{t}^{t+h} dt' H(t')$ in its taylor series, $$H(t)h + \frac{1}{2}\frac{dH(t)}{dt} h^2 + \frac{1}{3!}\frac{d^2H(t)}{dt^2} h^3 + \frac{1}{4!}\frac{d^3H(t)}{dt^3} ...
0
votes
0answers
10 views

How to plot Joukowski airfoil?

We have an asymmetric potential flow past the cylinder (i.e. 2D circle) of radius $R$ of well-known complex velocity $W$: $$ \tilde{W} = v_\infty e^{-i\alpha} + i\frac{\Gamma}{2\pi(\zeta - \mu)} - \...
5
votes
0answers
18 views

What's the intuition behind the Choi-Jamiolkowski isomorphism?

What is the intuition behind the Choi-Jamiolkowski isomorphism? It says that with every superoperator $\mathbb{E}$ we can associate a state given by a density matrix $$ J(\mathbb{E}) = (\mathbb{E} \...
0
votes
1answer
41 views

Quantum entanglement of spins

Suppose we have a pair of spins in the state $\left|\Psi\right>=\frac{1}{\sqrt2}(\left|\uparrow\downarrow\right>-\left|\downarrow\uparrow\right>)$. We know that the measurements of the spins ...
0
votes
1answer
136 views

What will happen to the center of mass of the human body when a person carries a weight with one hand?

What will happen to the center of mass of the human body when a person carries a weight with one hand a briefcase for example. Wouldn't the center of mass move horizontally towards the side carrying ...
239
votes
22answers
83k views

A mirror flips left and right, but not up and down

Why is it that when you look in the mirror left and right directions appear flipped, but not the up and down?
-3
votes
4answers
33 views

Is earth continuously changing its orbit size i.e, circumference of the orbit?

One year have 365 days, but in leap year we have 366 days. Does that mean earth is continuously change its orbit size for every four years. like . 365.0 -- 365.1 -- 365.2 -- 365.3 -- 365.4 -- 365.5 -- ...
9
votes
10answers
1k views

“Reality” of length contraction in SR

I was in argument with someone who claims that length contraction is not "real" but only "apparent", that the measurement of a solid rod in its rest reference frame is the "real length" of the rod and ...
8
votes
5answers
657 views

Newton's 3rd law… hitting drywall (which I break) vs hitting a brick (which breaks me)?

According to the Third Newton's law of motion: For every action there is an equal and opposite reaction. So, I understand that if I hit a brick wall with $50\, \mathrm{lbs}$ of force, the ...
0
votes
0answers
19 views

RWD Differential steering and front wheels

I am developing a proof of concept autonomous car that will have 4 fixed wheels i.e. non mechanical steering. I will use rear wheels for drive and differential steering. My query is that when I want ...
-3
votes
0answers
30 views

The energy of tides: how does it affect the orbit of the Moon?

There are a few posts here at PSE that explain how the energy of tides comes at the expense of the Moon/Earth angular momentum. There is something that escapes me: how can angular momentum or KE be ...
2
votes
1answer
58 views

What is the program of quantum field theory? What is its derivation?

Paraphrasing Griffith's: For some particle of mass m constrained to the x-axis subject to some force $F(x,t)=-∂V/∂x$, the program of classical mechanics is to determine the particle's position at any ...
0
votes
1answer
45 views

Thermal mass and Thermal Width

I have a question about understanding the physical interpretation of the thermal mass and width of a particle. If we consider a particle in a plasma (which lets say is in the early universe and so ...
3
votes
1answer
181 views

Do primary first class constraints change the electric field in the Hamiltonian form of Maxwell's theory?

In my understanding of Dirac's theory of constrained Hamiltonians, the primary (and also the secondary) first class constraints are generators of canonical transformations that do not change the ...
1
vote
0answers
12 views

Poisson brackets among derivatives in the constraints of the Hamiltonian formulation of General Relativity

The issue I have is from the Hamiltonian formulation of General Relativity (GR) and concerns calculation of certain Poisson brackets. In this formulation, we have the 3-dimensional metric $h_{ij}(x)$ ...
0
votes
1answer
147 views

If I was to poke two holes in a water filled balloon would it lose water twice as fast a a balloon with one hole?

if I was to assume that the only force behind water coming out of the holes is the pressure i.e., the height of the water remaining which is constantly changing (declining) as water leaves the balloon,...
1
vote
1answer
65 views

How to use Heisenberg to explain atom cannot be at rest

In a Dutch national physics exam at the level just before entering university there was a question about a molecule HI: one atom hydrogen plus one atom iodine. Within the molecule, the hydrogen ...
5
votes
1answer
475 views

Origin of strong force

Today in class we were discussing the strong nuclear force, and our teacher was explaining about how the strong nuclear force counteracts the repulsion force between protons in a nucleus. When asked ...
-3
votes
1answer
21 views

Max Weight the Lid of a Vacuum can Hold

I have a box with a lid that has a mass object inside of it. I will be creating a vacuum inside of it with a $4~\mathrm{HP}$ Shop Vac that has a sealed pressure of $59~\mathrm{psi}$ and an airflow of ...
2
votes
1answer
29 views

What is the root mean square energy?

How the root mean square energy of nucleon in a nucleous of atomic number A in ground state is depend on A ?
-2
votes
2answers
66 views

Origin of time or origin of space-time? [on hold]

Are there alternate theories or models that contradicts the idea that big bang is the origin of time ?
-2
votes
1answer
30 views

what happens to a substance when I bombard it with electrons?

What will happen to a gas when I bombard it with an electron beam? Will there be a reaction?
1
vote
0answers
17 views

Optimal axis of rotation of a baseball for lateral movement

Suppose a baseball travels at 90 mph; what is the ideal axis of rotation for lateral movement of the ball? (two-seamer or cutter). So far I think that the following factors play a significant role in ...
0
votes
0answers
18 views

Can signal transmission from mobile phones affect battery life of other devices?

Sometimes I hear that you shouldn't keep devices that contain certain batteries close to your mobile phone continuously since signal transmission can affect the lifetime of those batteries. Is this ...
0
votes
1answer
28 views

Kinematics of Rectilinear Motion

A car leaves an outpost and reaches a speed of $60 m/s$ with a constant acceleration of $3 m/s^2$. It continues at this speed for a time then decelerates at $4.2 m/s^2$. How far will the car be after ...
2
votes
1answer
412 views

Right hand solenoid example

I am just studying for my physics final exam. I came across this example and am not satisfied with the answer. My answer is that Z is South and the current would flow from Y to X because of the ...
0
votes
0answers
30 views

Action variables in canonical transformations

Let's suppose we have a Hamiltonian $H(p_k, q_k)$ and we want to transform it via a canonical transformation to one Hamiltonian which doesn't depend on the new coordinates $w_k$, but only in the ...
3
votes
2answers
94 views

What kind of effect would cosmic expansion have on planetary motion or keplerian orbit?

The question is, if two following phenomena are thought to effect to the motion of the planet that orbits a star: Celestial body is pulled by some massive star by ordinary Newtonian gravity: $$ m \...
0
votes
1answer
16 views

Exact expression for the ground state energy in the 1D Bose-Hubbard model

I heard that Bose-Hubbard model is exactly solvable in 1D. What is then expression for the ground state energy $E_{0}(N, M, ...)$ as a function of total number of particles $N$, number of lattice ...
2
votes
2answers
272 views

How to find Tangential/Radial/Angular Velocity for motion in any curve?

Is the radial velocity responsible only for changing distance between objects and the component perpendicular to it only for change in direction? If so why? Please try to give a different explanation ...
13
votes
5answers
1k views

Complex integration by shifting the contour

In section 12.11 of Jackson's Classical Electrodynamics, he evaluates an integral involved in the Green function solution to the 4-potential wave equation. Here it is: $$\int_{-\infty}^\infty dk_0 \...
-2
votes
2answers
59 views

How do Rabi oscillations act on the relative phase of state kets

Suppose we have a system with a lower state $\left|{\downarrow}\right\rangle$ and and upper state $\left|{\uparrow}\right\rangle$, coupled by a pulsed electromagnetic field. I thought that from an ...
2
votes
1answer
20 views

Proving the definition of optical throughput

Optical throughout is defined by SPIE as $$\Gamma = \frac{EP\times EW}{S^2}$$ where $EP$ is pupil area, $EW$ is window area, and $S$ is the separation between $EP$ and $EW$. I have not been able to ...
7
votes
4answers
3k views

Is there any example where electric and magnetic fields are not perpendicular?

Perpendicular electric and magnetic field creates light or other electromagnetic waves. Is it a necessary property to have a perpendicular fields? If not what would happen when the fields are not ...
5
votes
1answer
43 views

What causes more damage, a head-on car crash at 30km/h or one car at 60km/h crashing into a stationary one?

Which will cause a greater impact? Two identical cars colliding head on (in opposite directions), each going at 30km/h OR One car travelling at 60km/h colliding into a stationary car (for the ...
3
votes
1answer
277 views

Physics of detection of coherent light in an incoherent background using the more compact Fabry Perot interfeometer?

I read University Of California Berkeley Professor J. Bokor's Chapter 7 course notes , shown below as an imgur image , on Temporal Coherence tonight. I am sending an email to Professor J. Bokor ...
7
votes
1answer
60 views
+50

Charge balance and Bogoliubov quasiparticles

Before trying to understand charge imbalance in superconductors (eg Hübler et al., Phys. Rev. B 81, 184524, Quay et al., Nature Physics 9,84–88 (2013)) I thought I had better check I understand the ...
5
votes
3answers
2k views

Torque direction meaning

I apologize if this question is dumb, but I've looked all over for a straightforward answer and either I can't find one or the terms are too complex for me to understand. I have only a rudimentary ...
15
votes
3answers
4k views

What on Earth is this drawing of Venus?

The Wikipedia article for Venus's alleged moon Neith has this picture: And a tantalizing remark regarding paramecia (vandalism?). I know the grey ball is supposed to be Neith, the white is Venus, ...
2
votes
1answer
28 views

Does the re-arrangement of chemical bonds happens due to electromagnetic interactions?

The question is of some interest because the storage of energy in a recharable battery is not caused by gravitational (potential) nor by kinetic energy. From this question Why is current the same in ...
2
votes
1answer
31 views

Switching Parity in a Superconductor

I've got a pretty simple question that's been bothering me for a while. This is the issue. Suppose we have a superconductor with phase $\phi$, and we change this to $\phi+2\pi$. One would think that ...
2
votes
2answers
81 views

Source of Dark Energy.

In accelerated expansion dark energy play a crucial role because of negative pressure, but during expansion Dark Energy(DE) do not dilute. DE density is independent of scale factor unlike matter and ...
3
votes
2answers
82 views

Gravitational Strength on a theoretical flat planet

Ok, so let me clarify: a planet that overcame all structural problems with being planetary size, I.E. collapsing into a ball. What would be the gravitational strength on a flat planet with the ...
1
vote
2answers
34 views

Formula for discontinuity of electric field across boundary

The formula for the discontinuity of the electric field across a boundary is given by$$\vec{E}_{\text{above}} - \vec{E}_{\text{below}} = \frac{\sigma}{\epsilon_0} \hat{n}.$$ In the derivation of this ...

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