2
votes
1answer
139 views

Is there any other superfluid element except helium?

Is there any other superfluid element except helium? Everywhere we see and speak about superfluidity, we just speak about superfluid helium. but is't there any other element or material or system ...
1
vote
1answer
71 views

Why is the elemental volume of a sphere equal to $4 \pi r^2dr$?

I was doing this question on calculating the electric field at a certain point in a sphere (length $r$ away from the centre), where the charge density is given by an equation. When I checked the ...
0
votes
1answer
42 views

Part/Object Geometry

Given Inertia Tensor, Principal axes vectors, Center of Gravity, and the Moments. Is it possible to obtain object/part dimensions?
0
votes
0answers
49 views

Expansion of solids on heating

I read that when we heat a solid, it expands! Based on circumstances it can expand in area, length and volume! My question is , that do they expand to a certain extent or keep on expanding, if we ...
0
votes
0answers
50 views

Differences between empiric laws of Galileo and Kepler

Although in both cases we encounter empiric laws, as far as I know Galileo's laws of motion differ in some way from Kepler's laws of planetary movements. In what way?
0
votes
1answer
41 views

How to write magnetic dipole transition hamiltonian using ladder operator?

The magnetic dipole transition Hamiltonian is $\hat{H}=\frac{e}{2m_ec}\hat{\mathbf{B}}\cdot\hat{\mathbf{L}}$ How do I express it in terms of ladder operator $\hat{L}_+$, $\hat{L}_-$, and the ...
2
votes
0answers
35 views

Mermin Inequality

Suppose I want to calculate the maximum of Bell inequality for three parties system. In this case I will have 6 measurement directions (unit vectors). It has been done in the paper PHYSICAL REVIEW A ...
0
votes
0answers
17 views

Why can't our universe be spherical? [duplicate]

if we happen to follow the bigbang singularity hypothesis, when he explosion occured shouldn't it expand in all directions. Seemingly our universe shouldn't have any boundaries. I searched for the ...
0
votes
1answer
87 views

Why are we not able to visualize Dimensions beyond 3 (or maximum 4 including time)?

We consciously know and feel the first three dimensions and with some thinking time as well. But according to literature like String theory etc., we have many many more dimensions. We can readily ...
1
vote
0answers
48 views

Normal coordinates for harmonic approximation (classical lattice vibration)

I am reading Jenő Sólyom's "Fundamentals of the Physcs of Solids" vol. 1. and i am very much stuck at this point (chapter 11.3.2 in the book): In the harmonic approximation the potential energy of a ...
0
votes
1answer
30 views

Electrostatic potential due to two charge system

When we calculate electric potential energy of a two particle system, say first I bring $+q_1$ and then I bring $+q_2$ against $q_1$'s electric field. Say I get that $q_2$ charge to a point $r$ ...
0
votes
1answer
156 views

Bead on a rotating wire - Conservation of angular momentum, fix points

Lets consider a wire in the x-y plane which rotates with constant angular velocity $\omega$. The coordinates of a bead, which is forced to stay on this wire, can then be expressed as $$x=r \cos(\phi) ...
0
votes
0answers
55 views

Is the Big Bang notion compatible with the flat space? (A problem with the **moment** of Big Bang, not with the place of it) [duplicate]

A passage from a paper: "If one imagines running the clock backward in time, any given region of the universe shrinks and all galaxies in it get closer and closer until they smash together in ...
0
votes
1answer
82 views

Is it better to walk or run when there is rain? [duplicate]

When I was coming from school to my house, there was heavy rain. Then one of my friends said "Don't simply walk, run fast". Then the question came to my mind: how should I go so as to avoid wetting: ...
1
vote
2answers
128 views

Can pressure be negative? [duplicate]

From Wiki and from physics fundamentals lections I received info that pressure is scalar value. But in definition you have relation between projections of two vector values to normal axe-force and ...
-2
votes
2answers
97 views

The physics of tripping on a stone [closed]

You know, you are walking or running at a certain velocity, your foot gets stuck on an obstacle and you end up flat-faced to the ground. What is the physics behind it? How does the linear motion ...
2
votes
3answers
207 views

Why doesn't a global frame of reference exist for GR?

I only have at best a layperson's familiarity with GR, so forgive me if I am asking a basic question, but I have heard that in GR, we cannot have a global frame of reference, that is a frame of ...
1
vote
1answer
117 views

Explanation of van der Waals force

Can someone please explain why the van der Waals force is attractive instead of repulsive? My understanding is that is has to do with the electron cloud creating a dipole, but I can't seem to ...
0
votes
0answers
56 views

Why did the reflection coefficient of quarter-wavelength coating depends on the indices of refraction

It was derived in page 428 of Optics by Eugene Hecht (4ed), that in the configuration below: where $$d = \lambda_f / 4 $$ The reflection coefficient R is So when $n_0n_s=n_1^2$, the reflection ...
0
votes
2answers
167 views

What is a good book to learn AP Physics C? [duplicate]

I am looking to learn AP Physics C (if you are not acquainted with the curriculum see here), both the mechanics part and the electricity/magnetism part. I have not had much exposure to an AP-style ...
0
votes
0answers
21 views

$H$ field in Faraday's law problem?

In my textbook it says, Consider a rectangular loop in the vicinity of an infinitely long wire carrying a current $I(t)$. To calculate the magnetic field, we can use the quasistatic approach, which ...
2
votes
0answers
49 views

Reference Needed: Time Dilation for Muons Reaching Earth's Surface

On the Hyperphysics Site we have the following page: Hyperphysics, "Muon Experiment", http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/muon.html which makes the following statement as its first ...
24
votes
4answers
5k views

What would put a harddisk drive (HDD) under 350G's of force?

I always see the label and it says 350G's withstandable. What would put this over 350G's? Is it even possible to hit 350Gs of force to a hard drive?
2
votes
2answers
141 views

Different signatures

I was working out the christoffel symbols, once where the metric that I am using has (+---) signature and another time where it has (-+++) signature because two books had different signatures and I ...
0
votes
1answer
214 views

The whole black vs. white T-shirt issue [duplicate]

I was outside with a friend the other day and we ended up talking about clothing choices in the heat, and he repeated the usual statement that one should wear white instead of black in order to stay ...
3
votes
0answers
74 views

Projector and delta function on a cycle $\Sigma$ of a manifold $\mathcal{M}_6$

In the paper ``Hierarchies from Fluxes in String Compactifications'' by Giddings, Kachru and Polchinski, the following example is considered for a localized source that may have negative tension (my ...
0
votes
2answers
111 views

Shimmering from heated air and the speed of light

A few months back, I was using binoculars to check if my friend was on his boat, which was around 2 to 3 km out to sea from the shoreline where I was standing. The images from, say the sail of the ...
3
votes
3answers
617 views

Do the planets really orbit the Sun?

This is a duplicate of this question on Space Exploration.SE. So why would I ask it again here? Read below. The question reads We often say that the planets orbit the Sun, which is usually a ...
0
votes
1answer
20 views

How to experimentally identify the exposed face of a crystal?

After depositing a material (e.g, TiO2) on a substrate, what methods can I use to check whether the material is crystalline, and what face (e.g, 001, 101, etc..) of the crystal is exposed?
0
votes
1answer
39 views

Polarization type/direction of $E$ field

I have an E field given as $E(z) = [xE_a - yjE_b]\exp(-jkz)$ and I know the answer is that the field is right-hand circularly/elliptically polarized depending on whether $E_a = E_b$. Can someone show ...
3
votes
2answers
304 views

Can temperature be a complex number?

Is it possible for a temperature to be a complex number? I want to say "no" but I can't be so sure. If it is possible I would like to know of an example. I found an interesting article which treats ...
2
votes
0answers
55 views

Ground state symmetry breaking in Bose-Hubbard model with spin-orbit coupling

The Hamiltonian for 2D Bose-Hubbard model with spin-orbit coupling on a square lattice is written as $ H = -t\sum_{\langle ij \rangle}\Psi_i^{\dagger}\Psi_j^{\vphantom{\dagger}} + ...
1
vote
2answers
84 views

Stationary v/s Static

Blau, in his GR book, says that a stationary and spherically symmetric metric is automatically static. He says this easily follows from the fact that for a stationary metric, and in spherical ...
2
votes
1answer
200 views

Hawking Temperature of the BTZ Black Hole

The metric of the BTZ Black Hole is given by $$ ds^2 = - N^2 dt^2 + N^{-2} dr^2 +r^2(d\phi + N^\phi dt)^2 $$ with $$ N^2 = -M+ \frac{r^2}{l^2} + \frac{J^2}{4 r^2}, \ \ \ \ \ \ N^\phi = ...
0
votes
1answer
64 views

Spherical Symmetric Metrics

In the case where all books try to illustrate a spherical metric, the procedure goes this way: First they impose isotropy in terms of polar coordinates so that one can write: $$ds^2=-A(r)dt^2 + ...
0
votes
0answers
41 views

How does the energy-momentum tensor transform under parity in 2D CFT?

I'm trying to get that if parity is conserved, the two represenations of Virasoro algebra which we get from $L_n$'s and $\bar{L}_n$'s starting from dilatation invariant Wightman theory have the same ...
0
votes
1answer
119 views

Are there any naturally occurring examples of photons without mass?

I read that a photon is said to have zero mass at zero velocity. Does this mean that they only exist in a state of probability until observed && interacting with some system? And then when ...
2
votes
1answer
63 views

What is $\mathcal{N}=2$ QED?

I would like to know is $\mathcal{N}=2$ QED is simply a $\mathcal{N}=2$ theory with gauge group $U(1)$ like in normal QED? If not, exactly what theory is it? Is there some reference for it?
2
votes
0answers
79 views

Torque on a wire loop from straight wire [closed]

I need to show that the torque on this wire loop is $$N = \frac{\mu_0}{\pi} 2abdII' \frac{(b^2+d^2)\sin(\theta)}{b^4+d^4-2b^2d^2\cos(2\theta)}$$ The where $\theta$, is the angle between the loop ...
0
votes
3answers
140 views

Angular acceleration - radial & tangential

Since ever I knew that radial (angular acceleration) is equal to $ W^2 * R = V^2 / R $ and that the tangential depends in the situation (School physics & calculus). Recently I encountered the ...
2
votes
1answer
70 views

Probability of Vacuum Fluctuations near Charges

A short, simple enough question, if you know about field theory, which unfortunately I don't. Are vacuum fluctuations more probable near a charge, for example an electron with negative charge? I ...
1
vote
1answer
74 views

Would Hund's rules still be valid if the electron had spin 3/2?

One of my homework assignments in atomic physics was the following: Given electrons had a Spin of $S = 3/2$, what would be the number of the first 4 noble gasses (complete shells)? The obvious ...
1
vote
0answers
47 views

Cylinder swinging in a halfpipe [closed]

I'm having a problem while solving this exercise: Consider a cylinder of radius 'a' swinging in a halfpipe whose radius = 10a. Find the equation of motion of the cylinder using the angle $\phi$ ...
2
votes
1answer
177 views

Learning physics from a strong math background? [closed]

I have a master's degree in operations research and took several PhD level math courses. In particular I'm most familiar with analysis/measure theory, probability theory, and stochastic processes, and ...
1
vote
1answer
132 views

Calculating electric field using a given magnetic field equation (Maxwell-Faraday law)

The following magnetic field is given (and nothing else is known): $$ \begin{cases} B_0 \frac{t}{T} & \quad\quad\quad r < R \\ 0 & \quad\quad\quad r > R \end{cases} $$ I need to ...
-1
votes
1answer
42 views

Calculating time dilation

I'm writing a science fiction story where the protagonist's experience requires long intervals between events. My plan is to put him/her/it on a spaceship between events at an appreciable percentage ...
1
vote
2answers
220 views

What is the qualitative cause for a driven oscillator to have a max. amplitude during resonance?

The steady-state motion of a driven oscillator is given by;$$x =\underset{\text{amplitude}} {\dfrac{F_0}{m({\omega_0}^2 - {\omega}^2)}} \cos\omega t.$$ As we see, the amplitude becomes maximum when ...
0
votes
0answers
58 views

Laser output below, just above and way above threshold?

I've been reading up on lasers recently and learnt that within the cavity while the laser light is amplified by the gain coefficient, it loses power due to transmission and absorption. Suppose the ...
0
votes
4answers
110 views

Photon field interaction

I want to know is there interaction between photon and electric or magnetic field? In other word can I deflect photons by electric or magnetic field? If it is possible, under which condition one can ...
2
votes
0answers
52 views

Why do certain types of sound seem to fade faster? [duplicate]

I noticed that if I'm playing music in a room and I go into another room or walk further and further, then at some point I can only hear the percussion and the melody to a lesser extent. All the ...

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