5
votes
1answer
10k views

What happens to the temperature of the water when you add salt to a bowl of melting ice?

If you have a bowl of ice that's melting, so the ambient temperature is just above 0 °C, what happens to the temperature of the water when you add salt? I know that the freezing point of salt water ...
2
votes
1answer
1k views

Can traditional steam (water vapour) exist in a vacuum?

Can steam (water vapour) exist in a vacuum, and if so does it look and behave the same as in air? Let's assume the actual case is a kettle boiling in a vacuum. Note that I'm talking about a gas-less ...
0
votes
1answer
160 views

What is the electric current $I_{12}$ and voltage $U_{12}$ in following electric circuit? [closed]

What is the electric current $I_{12}$ and voltage $U_{12}$ in following electric circuit? $I_{12}$ and $U_{12}$ are between points 1 and 2. . I have used this in constructing this electric circuit ...
0
votes
1answer
1k views

How does an inflationary universe solve the Flatness Problem, Horizon Problem and Monopole Problem? [duplicate]

Possible Duplicate: What is the evidence for Inflation of the early universe? I am reading some public science books on inflationary universe, e.g. The Inflationary Universe by A. Guth. ...
2
votes
1answer
153 views

How exactly are the different motions of only one kind of fundamental string assumed to give rise to the spectrum of elementary particles we observe?

In string theory, it is assumed that all particles can be described as quanta corresponding to the excitations of only one kind of fundamental string. How can in principle the different motion ...
2
votes
0answers
61 views

What is (or where can I discover) the Burke Potential?

I have very much enjoyed William L. Burke's Applied Differential Geometry. Reading around on the web it seems that he discovered something which is called the (retarded) Burke Potential, but I have ...
1
vote
0answers
105 views

How to derive the divergence leading to Kohn anomalies?

I'm trying to understand the mathematical derivation given in the book "A Quantum Approach to Condensed Matter Physics" on page 215 (see 1), for explaining how the phonon-energy perturbed by ...
1
vote
1answer
99 views

is Bohr-sommerfeld formula valid if the potential is non-smooth?

let be a non-smooth potential , for example a linear combination of step functions $$ \sum_{n=0}^{10}H(x-n) $$ my question is, for this potential would be Bohr-sommerfeld quantization formula valid ...
7
votes
4answers
940 views

Non-Integrable systems

Integrable systems are systems which have $2n-1$ time-independent, functionally independent conserved quantities (n being the number of degrees of freedom), or n whose Poisson brackets with each other ...
1
vote
1answer
76 views

Böotes Void and Dark Galxies

Wouldn't it be possible that Böotes Void, a space we generally consider to be "empty" be filled with a number of undetectable dark galaxies?
2
votes
2answers
120 views

A thought about Quasars

If Quasars are "beams" of energy exiting a super-massive black hole, in order for them to get through the black-hole's event horizon, they'd have to be traveling faster than the speed of light. My ...
0
votes
0answers
360 views

Reflectance and phase shift vs incident angle and wavelength

Plot the refectance and phase shift on reflection $\varphi$ for p and s polarized light versus incident angle $\theta$ for various wavelength $\lambda_1=.., \lambda_2=..,..$ in the simple case of ...
4
votes
1answer
165 views

Could we have assumed the speed of light to be different in different reference frames?

Ptolemy's model of universe assumes that our earth is the static center of universe and everything else move relative to it (ref: The grand design ch:3). This model would give us a consistent picture ...
16
votes
2answers
783 views

Does the exact string theory $S$-matrix describe all physics there is?

Suppose someone manages to evaluate the string theory $S$-matrix to all orders for any and all vertex operator insertions including non-perturbative contributions from world-sheet instantons and ...
8
votes
2answers
655 views

What does “particle number conservation” mean in condensed matter physics?

What exactly does it imply about a condensed matter system to have particle number conserved or not conserved? For example, why does the superconducting phase break particle number conservation while ...
1
vote
1answer
238 views

Modeling linear spring deformation in time

Suppose I had a spring (at equilibrium) and applied a certain force $F$, causing it to undergo elastic deformation. I know that by applying this specific force, hooke's law tells me that the spring ...
0
votes
1answer
252 views

Analysis of the impulse of 2 colliding carts under the effect of magnetic repulsion

Hi there! I have a question about an experiment that was conducted. It is related to momentum. 2 carts were put on a track on opposite sides. They were then propelled towards one another at ...
1
vote
2answers
390 views

Refractive index inside a fibre

The refractive index $n$ of a fibre is calculated as; $$ n = c_0/c_m $$ Where $c_0\approx 300000km/s$ is the speed of light in a vacuum, and $c_m$ is the speed of light in the fibre in question. How ...
5
votes
4answers
329 views

Physics background for Quantum Mechanics

Very often on this site people ask what background in math is needed to be able to understand quantum mechanics (based on a short search of this site). So that question is answered. However, I want to ...
17
votes
5answers
592 views

Is it really a particle?

Forgive the stupid question but when colliding particles together, how does one know that a particle is actually a new form of sub-atomic matter and not simply just some shattered fragment of the ...
3
votes
2answers
2k views

Can entropy be explained in terms of a cleaning/keeping your room clean?

I'm trying to relate the concept of entropy to keeping my room clean as suggested by my high school teacher ~1993... Comparing the two scenarios: Every day I come home and throw an empty can on the ...
0
votes
0answers
197 views

Colliding bubbles in hyperspace

Assuming the following A universe is the surface from a bubble in hyperspace. Inside a bubble there is nothing, only the surface represents a universe. The size of the bubble is time. Dark matter is ...
2
votes
1answer
1k views

Thermal expansion of Sphere

How would one go about writing an expression of the expansion of the volume of a sphere of a given material? I noticed a few sources give it as $\Delta V= 3\gamma V\Delta T $ where V is the initial ...
1
vote
1answer
933 views

Branes Collision -> Big Bang

Imagine universe occurred when two parallel branes collided, Momentum of Branes converted to big bang kinetic energy after Collision. Thus, high-energy quanta are high-Vibrating strings. what ...
2
votes
1answer
46 views

Variational approach to search the excitations. What will happen if start from wrong reference state?

By 'wrong reference state' I mean a state which cannot be transformed into desired ones via variational ansatz $\left|\Psi\left[\mathbf{n}\right]\right\rangle ...
-1
votes
2answers
161 views

What is current of electric circuit which has only one component - a battery (or cell)? [closed]

What is current of electric circuit which has only one component a battery (or cell)? Explain why.
6
votes
1answer
605 views

Meaning of the word “Moment”?

This question is more of a question about the origin of a physical term moment used in many contexts. My question is about the linguistic or historical meaning of the word "moment". Please don't ...
4
votes
1answer
261 views

What interaction does a Fayet-Iliopoulos coupling parameterize the strength of?

Couplings give the strength of interactions. They appear in a Lagrangian as a coefficient to the two (or more) interacting fields. Unfortunately, I'm struggling to find a source that describes what it ...
1
vote
1answer
379 views

Electromotive force

EMF is defined as: "The potential difference across the terminals of a battery or dry cell when it is giving no current to the circuit." So, if current starts to flow from the ...
1
vote
0answers
299 views

Angular momentum confusion

Could somebody please explain what is going on here? We have a system of two indistinguishable spin-1 bosons. We shall adopt the center of mass frame. Let $S$ = total spin $L$ = relative orbital ...
3
votes
2answers
3k views

Electric field and electric potential of a point charge in 2D and 1D

in 3D, electric field of a piont charge is inversely proportional to the square of distance while the potential is inversely proportional to distance. We can derive it from Coulomb's law. however, I ...
4
votes
0answers
150 views

Hemispheric dichotomy of Mars and unstable spin axis

Is the following explanation plausible? Can you spot any flaws? Mars doesn't have a large moon to stabilise its axis of rotation. At some point early in its formation its axis might have been ...
7
votes
2answers
1k views

Photon energy - momentum in matter

$E = h\nu$ and $P = h\nu/c$ in vacuum. If a photon enters water, it's frequency $\nu$ doesn't change. What are its energy and momentum : $h\nu$ ? and $h\nu/c$ ? Since part of it's energy and momentum ...
3
votes
1answer
212 views

Question on Section 9.1.3 in “Conformal Field Theory” by Philippe Di Francesco et. al

Question on Section 9.1.3 in "Conformal Field Theory" by Philippe Di Francesco et. al. The basic idea of the Coulomb-gas formalism is to place a background charge in the system, making the $U(1)$ ...
1
vote
0answers
78 views

Energy distribution between long- and shearwaves after refraction of sound

From this explanation, I learn that sound is refracted according to Snell's Law upon passing a border between materials of different sound speed. I also learn that upon passing the border, a mode ...
1
vote
2answers
352 views

Are the intersections of past and future light cones spacelike?

Given a timelike reference worldline (not necessarily geodesic), we can define light-cone coordinates $\tau^+$ and $\tau^-$ so that the 3-D hypersurfaces of constant $\tau^+$ are past light cones of ...
4
votes
2answers
5k views

How does rubbing cause the transfer of electrons from one object to the other? [duplicate]

I have just learnt about electrostatics. Why would there be a transfer of electrons? Is it because of the difference of the materials (i.e. triboelectric series)? So in the case of two different ...
1
vote
1answer
535 views

Dipole moment of the electron

I've read that there are some restrictions on the value of a possible intrinsic electric dipole possessed by the electron, but isn't the dipole value dependent on the electron's wavefunction? Assuming ...
3
votes
1answer
90 views

image distortion when taking a picture from space

I'm trying to understand if there is a distortion of an image taken from space (i.e. from a satellite), and if there is, then how to model it mathematically (depending on the angle in which we take ...
4
votes
1answer
4k views

The formula of the force exerted on an electric dipole by non-uniform electric field

When an electric dipole of moment $\mathbf{P}$ is located in a non-uniform electric field $\mathbf{E}$, there is an net force exerted on it. However, the formula of the force in some books is read ...
0
votes
1answer
86 views

Physics Impulse

This is the problem I am dealing with: "One of the functions of an automotive air bag is that it lengthens the collision time. Without an air bag, suppose the 100Ns impulse of a collision is taken up ...
13
votes
5answers
971 views

Octave equivalence: biological or more?

I'm a graduate student in mathematics doing a bit of research in signal processing and Fourier analysis and I've come across a question that could probably be better answered by a physicist: Is the ...
0
votes
0answers
237 views

I'm having trouble understanding the dimensions of this falling body problem

I'm working with this: A 50 kg mass is shot from a cannon straight up with an initial velocity of 10m/s off a bridge that is 100 meters above the ground. If air resistance is given by 5v ...
1
vote
1answer
183 views

Strange Behavior in Spring Computer Model

To learn more about oscillatory motion which I am learning about in my high school physics class, I have created a computer model of a damped spring where the damping force is proportional to ...
3
votes
1answer
166 views

Why does the Gallum-Arsenite bandgap narrow for higher temperatures and is this because of unavoidable impurities?

I found this sentence: GaAs at 300K contains 10^15 acceptor atoms per cubic centimeter. The bandgaps for Gallium Arsenite are: 0 Kelvin : 1.518 eV 300 Kelvin: 1.424 eV Now I am wondering: ...
4
votes
5answers
2k views

What is force? How does a constant force output a nonconstant power?

For a constant force, P=Fv. I understand the mathematical derivation of this, but this seems to me, intuitively, to be nonsense. I feel that my discomfort with this comes from a fundamental ...
2
votes
1answer
236 views

Perturbation method & eigenvalues

I have a problem but I don't understand the question. It says: "Show that, to first order in energy, the eigenvalues ​​are unchanged." What does it mean? It means that if the Hamiltonian has the ...
4
votes
2answers
415 views

How do I define time-ordering for Wightman functions?

This is a follow-up question to What are Wightman fields/functions Ok, so based on my reading, the field operators of a theory are understood to be operator-valued distributions, that is, to be ...
1
vote
2answers
276 views

Is there a “present state” of distant stars if simultaneity is relative?

Special relativity theory says simultaneity is relative, meaning that different observers will not agree on what happened first and what second. Does it then make sense to say that looking at distant ...
1
vote
4answers
2k views

Statistics in physics

What are the uses of statistics in physics? I am about to embark upon a study of statistics and I would like to know what the particular benefits I gain in physics.

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