0
votes
0answers
44 views

How stable is a tablespoon of neutrons once removed from a neutron star? [duplicate]

I've often heard public lectures describing the degenerate, exotic matter left behind after a star collapses but fails to go supernova; one that has found its way to become a neutron star. The speaker ...
1
vote
1answer
49 views

4-momentum of photon

The 4-momentum is defined as $p=mU$ where m is the rest mass of the particle and $U$ is the 4-velocity. Now I am confused as to how this applies to a photon for which one can't define $U$ since there ...
-3
votes
0answers
39 views

Can something contain itself? [on hold]

Let's say I have a cardboard box. Let's call it box $A$. I can put things in this box -- I can put my glasses in, my shoes in, or my cat in. Can I put the box in the box? Let's call this "second box" ...
2
votes
2answers
101 views

Does “ac current” mean that the electricity goes left and right or just changes polarity?

AC goes one way in one phase and the opposite way in the other phase, but is going right and to left, or is it only changing the polarity from (-) to (+)? If light bulbs turn off and on (so fast we ...
1
vote
2answers
60 views

Are atoms compressible?

Liquids are not compressible, but what does compressible mean? Does it mean the increase in the density or decrease in volume? Or something else? Why are liquids incompressible, in a way nothing ...
2
votes
1answer
49 views

Solving wave equations with heuristic-like, analytic methods

Take a Klein-Gordon (KG) equation for a model exercise: \begin{equation}\frac{\partial^2 u}{\partial t^2}=c^2\frac{\partial^2 u}{\partial x^2 } - \Omega^2 u,\end{equation} with boundary and initial ...
2
votes
2answers
40 views

Different materials have different temperatures?

Why do two materials, under the same weather, have different temperatures? I have a small clue about it. For example, iron and wood supposed under the sun's radiation, and if we touch both of them, ...
2
votes
1answer
38 views

Work in gravitational field

I was doing a test a few days ago and there was a fairly simple task involving gravity basics. The task asks me to calculate the work done by moving an Earth's artificial satellite from a stationary ...
0
votes
0answers
12 views

Need better keywords to search for “polarization rotator” film

I want to replicate at home the demonstration that Ron Garret gave during his 2011-01-06 talk at Google1, featuring a "polarization rotator". My online searches have not turned up any suppliers for ...
1
vote
0answers
24 views

Yamabe flow, Metric times Scalar curvature? [migrated]

I was watching a lecture on differential geometry on Ricci flow, when someone asked a question about "Scalar curvature being multiplied by metric" to my understanding this shall be written as ...
1
vote
0answers
18 views

symmetry group of multi-electron atom

Neglecting spin effects, the energy levels of multi-electron atoms are characterized by states of definite total orbital ($L^2$) and spin angular momentum ($S^2$). From this it seems that the ...
0
votes
2answers
41 views

How to use a magnifying glas or any lens to enhance small light power?

I am currently trying to amplify a tiny amount of light so that a photodiode will recognize it. In order to amplify the light I thought about using a magnifying glass since I got to know that such ...
2
votes
0answers
47 views

Which is the true magnetic field?

In electromagnetism we have the $\mathbf{B}$ field which is the field appearing in the Lorentz force law: $$\mathbf{F} = q(\mathbf{E} + \mathbf{v}\times \mathbf{B})$$ and we have the $\mathbf{H}$ ...
1
vote
0answers
18 views

understanding magnetic dipole moment and torque [on hold]

I would like yo know if I understand things correctly: Magnetic moment, which is a constant value for a solenoid or magnetic dipole, determines the torque it will experience in a magnetic field. (I ...
-8
votes
0answers
54 views

particle physics and the problem with understanding [on hold]

Imagine a world that is watching ours, theory is theory , what if theory was real, why do we breath, physics is all theory until proven otherwise
1
vote
0answers
38 views

What mathematical structure describes superspace and superfields?

In every book related to supersymmetry I have encountered at some point the idea of superspace is introduced. Superspace is presented as a space spanned by 4 "normal" directions and 4 Grassmannian ...
0
votes
1answer
31 views

What is the typical strength of the electric field in a particle accelerator?

I am working on a research project involving the closed orbits of hydrogen in the presence of an external electric field and I am curious what a reasonable approximation for the electric field ...
0
votes
1answer
16 views

Magnetic field between two rings

Two rings are placed parallel atop each other along an axis with a distance $\epsilon$ which is much smaller than the radius of both rings a. Through one of the rings there is a current I and through ...
1
vote
1answer
37 views

Relativistic Lorentz Force with constant, perpendiuclar, and uniform E and B fields

I am trying to solve the following problem from the Fundamentals of Plasma Physics by Bittencourt (Problem 2.7): Analyze the motion of a relativistic charged particle in the presence of crossed ...
0
votes
0answers
14 views

Where are real limits of evaporative cooling?

There are many projects focused on utilising evaporative cooling for food preservation or computer cooling purposes. I have other thing in mind, however and that's cooling beer. Once you're outside, ...
0
votes
1answer
121 views

Definition of the “present” in physics (not “instant”) [on hold]

Instead of wondering about what time is, I'll just assume for the moment that it is a parameter describing the evolution of the universe. Observe then that there is a distinguished/preferred time, ...
0
votes
1answer
17 views

How close to the wavelength of light have to be to inter-planar spacing for diffraction to occur?

I'm doing past papers for my exam on Wednesday, and I've come to a question I'm stuck on. So, you have x rays of $\lambda = 0.25\,\mathrm{nm}$ incident on a cubic unit cell with lattice lattice ...
0
votes
1answer
21 views

How bright would the Earth be at night without the moon?

How bright would the Earth be at night without the moon? Specifically, how much light would reach the surface of the Earth at sea level?
1
vote
0answers
18 views

Could Bluetooth radio waves be used to pick up UV light [on hold]

i am a bit of a Physic novice. But i was wondering if someone could answer this and if they might be able to make a possible sugguest. i was wondering if it possible for a bluetooth to be able to ...
6
votes
2answers
107 views

Do bras and kets have dimensions?

I'm trying to understand more intuitively what bras and kets are, but some aspects of them remain a mystery to me. We usually think of $\psi (x)$ as having dimension of $[1/\sqrt{L}]$ so that ...
0
votes
0answers
7 views

Clarification on isotropic sources and fields

For an isotropic radiation field the net flux is zero, something I find quoted in a lot of notes and text on radiation. We often think of isolated stars as isotropic sources, but their net flux is ...
0
votes
1answer
21 views

Is a matter anti-matter collision comparable to Gamma Ray Burst (GRB) energy output?

Is a matter anti-matter collision (please assume two cosmological objects, neutron star sized say), the largest energy release method known? Would it be comparable in order of magnitude to gamma ray ...
0
votes
2answers
49 views

Why bumble bee cannot fly aerodynamically? [duplicate]

I just saw this pic So I got curious and logged in on physics.stack first time, is it true? I am a math major and usually wander on mathstack but I would like to understand why Bumble bee cannot ...
1
vote
0answers
31 views

Pumping water from a well [on hold]

I have water well $h_1=70~m$ below ground level. A cylindrical tube of diameter $e$ joins the well to a tank of height $h_3=10~m$, $h_2=1.5~m$ above the ground. The tank is initially filled with water ...
0
votes
0answers
17 views

A force in a homogeneous magnetic field [on hold]

Semi infinite parallel conductors, while on them without friction slides a crossbar . Perpendicular the plane of the conductors is a homogeneous magnetic field. To what extent of force we must act on ...
-2
votes
2answers
73 views

What's outside of the universe? [on hold]

Assuming you found a way and managed to accelerate above light speed without disintegrating, and went to the edge of the universe, what would happen? Would you instantly explode due to the lack of ...
13
votes
3answers
814 views

How many observations are needed to determine a comet's orbit?

Based on the following facts: We have Kepler's laws of planetary motion. We have a good knowledge of the positions and orbits of the gravitationally significant objects in the Solar System. We can ...
0
votes
0answers
29 views

Is there any matter inside an event horison? [duplicate]

Consider a feeding, growing black hole. We never observe any matter to cross the event horizon, because time stops there. All matter would be "stuck" in a sphere around the event horizon, slowly ...
0
votes
1answer
18 views

Magnetic field at a distance from a metal rod [on hold]

A massive metal rod of 4 cm has a current of 8000 A running through it and the current density is uniform. What is the magnetic field a distance 1 cm from the rod? Should I use the Biot Savart law and ...
0
votes
0answers
11 views

Derive phase shift equation for two diffirent optical paths differences

If we have two optical paths differences, call them $\phi_1, \phi_2$, and $\phi_1 > \phi_2$ then phase shift with respect to optical path difference $\phi_2$ is $PhSh = \frac{2\pi}{\lambda}(\phi_1 ...
30
votes
2answers
5k views

Is the Planck length the smallest length that exists in the universe or is it the smallest length that can be observed?

I have heard both that Planck length is the smallest length that there is in the universe (whatever this means) and that it is the smallest thing that can be observed because if we wanted to observe ...
0
votes
0answers
27 views

Can a magnetic field be expelled over long arbitrary distances through a super conductor? [on hold]

I'm not a physiscist but i have a creative concept I wish to make into a environmental commercial before my Interactive Feature Film. Apologies, if it sounds like I have no idea what I'm talking ...
0
votes
0answers
25 views

How to prove by symmetry that tension in a section of rapidly rotating wheel act tangentially?

Suppose a thin uniform wheel of radius $r$ is rotating rapidly about its axis; its spokes have almost negligible strength. According to the book, the centripetal force is provided by the tension ...
1
vote
0answers
19 views

Limits on the information obtained through optical measurements

Consider a Gedankenexperiment shown in the figure below. There are two lasers $S1$ and $S2$ with exactly the same specifications on paper. In practice, they are of course somewhat different but ...
2
votes
0answers
21 views

Is it possible to have a line rather than a point where the three states of a substance can exist?

Most of us are familiar with state diagrams that define which of the three states a substance will take given the pressure and temperature. And that some substances, such as water for example, exhibit ...
1
vote
2answers
66 views

Have two identical quantum mechanical experiments ever been done?

Have two experiments ever been done such that the set up is identically the same, (when I say identically I mean down to the atomic level). Of course the experiment would have to be very simple. If it ...
0
votes
0answers
25 views

Resources for Entanglement Entropy in Condensed Matter Systems and Black Hole Thermodynamics

Over the last month or so, I have set it upon myself to teach myself the AdS/CFT correspondence. In particular, I am interested in the connection between black hole entropy and entanglement entropy in ...
1
vote
0answers
7 views

Transformation Diagrams for Ceramics

So, in the field of metallurgy, there are a few varieties of phase diagram that are used to predict the post-processing characteristics of alloys. These include Time-Temperature Transformation ...
0
votes
1answer
53 views

Why can this question about Centripetal Force not be answered in this way?

Here is the question: "A car travels round a bend which has radius $100 m$ and is banked at an angle of $20°$ to the horizontal. The car is travelling at a speed of $30 ms^{-1}$. What is the least ...
0
votes
0answers
59 views
+50

single photon/electron double slit experiment, resetting the detector material after each impact

What is the experimental outcome of a single photon/electron double slit experiment under the constraint that after each detection the detector material is reset to the original state ie, in the ...
0
votes
0answers
13 views

images formed by refraction

While deriving the formula for image formation by spherical refractive surface we assumed that object is placed at the principal axis and is like a point object. What if the object is not placed at ...
0
votes
3answers
24 views

Trying to locate information on alpha particle scattering/peak resonance energies for elements

On our campus we have an ion beam analysis lab. It is used for compositional analysis through the firing of alpha particles at MeV energies at target samples. From here it is a simple matter of back ...
2
votes
3answers
91 views

What can change a photon's frequency?

I found this question: Is it possible to apply force to a light particle? As it states, gravity can change the frequency of light by changing its momentum. My question regards other phenomena that ...
0
votes
0answers
9 views

image motion for projectile motion of object

a ball is projected from top of the table with initial speed u at an angle of inclination 'a' to the table. describe motion of image with respect to the ball on a screen located next to the table My ...
0
votes
0answers
39 views

Can elementary particles be rightfully considered quasiparticles?

Can elementary particles rightfully considered quasiparticles? I have this association, because renormalization makes particle properties, like mass and couplings, energy-dependent quantities, even in ...

15 30 50 per page