Q stringlengths 18 13.7k | A stringlengths 1 16.1k | meta dict |
|---|---|---|
Confusion in least action in the following situation
I understand that when electric field is applied normal to the surface of a conductor the net electric field inside the conductor is zero.
But as shown in the diagram above, if electric field is not normal to the surface of a conductor, I see two possiblity of induc... | The field is always perpendicular to the surface of a conductor.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/483883",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Can I contract index in this expression? I'm reading Carrol text on general relativity, on page 96 they arrive to the term
\begin{equation}
\frac{\partial x^{\mu}}{\partial x^{\mu '}}\frac{\partial x^{\lambda}}{\partial x^{\lambda '}}\frac{\partial^2 x^{\nu '}}{\partial x^{\mu}\partial x^{\lambda}}.\tag{1}
\end{equatio... | No, you can't.
$$\frac{\partial x^{\mu}}{\partial x^{\mu '}}\frac{\partial x^{\lambda}}{\partial x^{\lambda '}}\frac{\partial^2 x^{\nu '}}{\partial x^{\mu}\partial x^{\lambda}}$$
can be re-written as :
$$\frac{\partial x^{\mu}}{\partial x^{\mu '}}\frac{\partial x^{\lambda}}{\partial x^{\lambda '}}\frac{\partial}{\parti... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/483984",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 2
} |
How are these two versions of the conservation of angular momentum different? Here are two versions of the conservation of angular momentum.
*
*The total angular momentum is constant if there is no external moment on the system
*The total angular momentum of a particle is constant if it is only under the influence ... | These two statements refer to two different entities. Statement # 1 applies to a "system" which can be a complex entity of significant spatial extent. Statement # 2 applies to a "particle" which usually means a point particle or a system that can be approximated by a point for the purposes of the problem.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/484066",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
Why do the tyres of the vehicles burst during summer? The explanation of most is -According to Charles' law if the temperature increases volume should also increase and hence the tires burst. But it is also that if volume increases pressure decreases (Boyle's law). So the pressure of the gases should lessen and hence t... | The volume increase of the tyre when it's hot is small, and so the pressure increase in a hot tyre is significant.
In addition, high temperatures cause rubber to weaken, which increases the chance that the tyre will pop.
By far the worst situation for a tyre is when it is not only hot, but also rolling at speed. In th... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/484189",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 0
} |
Where does the Master equation for the derivation of the Fokker-Planck equation come from? I'm participating in an introductory course for biophysics. We briefly discussed the derivation of the Fokker-Planck equation and used the so-called Master equation as a starting point.
$$
\frac{\partial P(x)}{\partial t}=\int \... | The master equation is summarized in words as follows:
The rate of change of the probability of one state occurring is equal to the rate at which transitions occur into that state minus the rate at which transitions occur out of that state.
This is one of those situations where it's useful to think of probability as ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/484403",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Induced Currents in Circuits I was given the following question:-
The plane figures shown are located in a uniform magnetic field directed away from the reader and diminishing. The direction of current induced in the loops is shown in the figure. Which one is the correct choice?
The correct answer is (D).
I am aware... | Well electromagnetism says three things;
1)relative motion between a magnet and a closed loop(circuit) creates current
2)orientation of magnet moving relative to a closed loop affects the direction of current
3)how fast the magnet is moving relative to a closed loop affects the rate of creation of cirrent
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/484587",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 1
} |
Why does the intensity of the scattered light vary when a monochromatic laser is shined into a transparent object? When a laser is shined into a glass ball such as this video (link) or a bottle of water (link) the light is refracted through the whole transparent body. However, the intensity of the light scattered to t... | What you are seeing is the glass acting as a light guide by capturing light by total internal reflection. These guided modes circulate the object and either escape by scattering at a defect or leach out over time (eg cladding modes in an optical fibre escape when its bent).
The scattering has a preference for coming ou... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/484733",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
Telling if Capacitors are in Parallel or Series
So C1 and C2 are in series. But if each one is placed in red boxes, they are in parallel?
It's confusing going jumping between current, capacitors, and resistance.
For me it's kinda confusing deciding which one is in parallel and which one is in series.
| There are no dumb questions, just bad teachers.
In your case, both capacitos are in series. IT doesn't matter if they are upside or in the red boxes, it's series.
How can you tell? This is a rule of thumb: you have to check if there is more than one possible path.
*
*Two elements are in series if they are one after ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/485009",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 6,
"answer_id": 0
} |
Energy Interpretation of Quantum Effective Action From Weinberg's "The Quantum Theory of Fields" In section 16.3 of Weinberg, he attempts to prove that the effective potential energy $V(\phi)$ is equal to the minimum energy density of a state with field expectation value $\phi$. I am confused about the very beginning o... | S-matrix theory (e.g. Weinberg's correct formulas) typically refers to the Heisenberg picture. OP is presumably thinking of the Schroedinger picture, and thereby obtaining opposite time evolution.
References:
*
*S. Weinberg, Quantum Theory of Fields, Vol. 2, 1995; Section 16.3.
*J.J. Sakurai, Modern Quantum Mechani... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/485188",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
If a black colored body absorbs all colors, why does the spectrum of light appear on a black shoe? Few days back in a 10 grade school practical, we were shown the dispersion of light by a prism to create spectrum.
Then we went into the open sun and performed it under a linear building roof and same results were obtain... | Assuming his shoe wasn't completely black (i.e. darker than a sunless cave) then in general some light is reflected. For example, if you can discern the texture of the fabric, then the shoe was not completely black and you can always expect to see some light reflected, although certainly not as much as light is reflec... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/485325",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Raychaudhuri scalar In Carroll's 'Space-time and Geometry', appendix F on congruences, the Raychaudhuri equation is derived.
However, in the process, I seem to miss a calculation step that changes the sign of the Raychaudhuri scalar.
Page 461, Carroll writes:
\begin{align} U^\sigma \nabla_\sigma B_{\mu \nu} &=U^\sigm... | I think it's a typographical error. He should have changed the sign of the Riemann tensor in the last two lines of his calculation (F.10). Then to obtain the Ricci tensor with the correct sign in the Raychaudhuri equation, you must interchange $\mu$ and $\lambda$, getting the required negative sign. This is because the... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/485881",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Creating a spatial variation of phase in a given superconducting sample Blundell's book on Magnetism, talks about the generalized rigidities as a general consequence of spontaneously broken symmetries. In this context, it mentions that in a superconductor the phase of the macroscopic wavefunction, $\phi$, is uniform ac... | Yes, there is a very simple way to introduce a gradient in the phase $\nabla \phi$, all you need is to have a current running in your superconductor (i.e. a supercurrent). If you have a constant current $\mathbf{J}$, and then you have a constant phase gradient.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/485993",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
Shooting someone's past self using special relativity Suppose A and B are a long distance apart initially. B takes off in a spacecraft in A's direction at a really high speed. Both were aged 0 when B took off. When B about to cross paths with A, A observes him to be 30 years old (while A is 60). At this point, 60 year ... | You suppose that A and B are far apart "initially" and that they were "both aged 0 when B took off". It means that you assume that simultaneity is an absolute notion, independent of the frame of reference, which is why you come to a paradox. It is exactly the symetric case of two people starting at the same point, dive... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/486760",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 1
} |
What is the CFT dual of the stress tensor in the bulk? I am new to AdS/CFT. I know that the dual of the bulk metric is the CFT stress tensor but what about the dual of the bulk stress tensor? I mean in principle one can extrapolate whatever bulk fields to the boundary and then compute the stress tensor's dual on the bo... | A short answer is that the boundary limit of the bulk stress tensor is simply the boundary stress tensor. But we could say a bit more in addition, coming from the 1999 paper by Balasubramanian and Kraus.
As usual, the stress tensor of the theory is $T^{\mu\nu} = \frac{2}{\sqrt{-\gamma}} \frac{\delta S}{\delta \gamma_{\... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/486845",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 2,
"answer_id": 0
} |
Is it possible writing conservation of relativistic energy in this naive way? Conservation of charge or rest mass can be written in this way and it is Lorentz invariant
$$
\nabla \cdot (\rho \mathbf{u}) + \frac{\partial \rho}{\partial t} = 0
$$
So we could be tempted to naively write conservation of energy in this way ... | In general you have to consider the stress energy tensor. If you want only energy conservation (without the stress and momentum part of the tensor) you can take $\partial_\nu T^{0 \nu}=\frac{\partial}{\partial t} \omega + \nabla \vec{S}/c=0$, where $\omega$ is the energy density and $\vec{S}$ the energy flow density.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/487168",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 3,
"answer_id": 2
} |
Is the highest photon energy currently possible a Planck photon or based on space-time quantinization? It makes sense that there could be an upper limit to the frequency/energy for individual photons if the universe as we know it is quantized.
But, the highest energy photons I've heard about have a frequency between $... | There are two issues here. Physics does not set an upper limit to photon energy, although at high energy particle antiparticle pair creation will in practice be limiting. If the universe is finite, then it has a finite energy that obviously cannot be exceeded by a photon.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/487228",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 0
} |
Is the velocity of the spinning rod constant after it's hit? Say we've got a rod floating around in space, with two masses of $m_0$, one attached at each end. Let's say the rod has a length of $l$.
There's another mass, $m_1$, moving at some velocity $v$ towards one of the masses.
$m_1$ collides and sticks instantane... | The shape of the object does not matter, whether it is a rod with different masses at each end, a round ball, or any other object, once set in motion, the rotation will be a constant RPM around the center of mass, and the linear motion of the center of mass will remain constant, unless acted upon by another force.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/487376",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 2
} |
Using symmetry of Riemann tensor to vanish components The Riemann tensor is skew-symmetric in its first and last pair of indices, i.e.,
\begin{align}
R_{abcd} = -R_{abdc} = -R_{bacd}
\end{align}
Can I simply use this to say that, for example, the component $R_{0001} = 0$ because $R_{0001} = -R_{0001}$?
| Yes. All the components where the first two indices are the same, or the last two indices are the same, are zero.
Sometimes it is useful to think of this tensor as a $6\times6$ symmetric matrix where the “indices” are $01$, $02$, $03$, $12$, $13$, and $23$.
However, don’t conclude from this that there are $6+5+4+3+2+1=... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/487514",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
What makes north pole of a magnet north pole in the first place? This question might seem absurd and illogical to many. But it just popped out in my mind while I was reading about magnetism.
-Like in case of charges, positive and negative charge on an atom means absence and presence of extra electrons respectively. So... | You are right up to a point about the charges on an atom,but you don't seem to understand what charge itself is. Charge is the source of a force vaguely similar to gravity, but trillions of times stronger. This force is called the electromagnetic force. Few people realise how powerful it is. In particles which can be o... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/487584",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 4,
"answer_id": 2
} |
Problem while constructing langmuir probe I am working on DC glow discharges and want to construct a langmuir probe. Circuit I am using is as shown in the picture
Also, I am applying ~1KV across cathode and anode.
Problem I am facing is that I am getting discharge btw probe and cathode. Which isn't unexpected, but des... | To get something useful with the langmuir probe you will need to match the potential of the probe to the local potential of the plasma - can you vary the Vp potential to get the full range of 0-1kV?? If you match the potential of the probe to the plasma potential then you should not get the extra discharge in my opinio... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/487791",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 1
} |
What is the change of entropy for a resistor at constant temperature? A 10 Ω resistor is held at a temperature of 300 K. A current of 5 A is passed through the resistor for 2 minutes. Ignoring changes in the source of the current, what is the change of entropy in (a) the resistor and (b) the Universe?
My attempt:
... | Since the resistor is kept at $T=300K$(which is wierd since its heating up), the entropy change of the resistor is
$$\Delta S_{resistor}=\frac{-\Delta Q}{T}$$
(heat flow out of the system taken -ve)
Since the surroundings stay at $T$(since no other temp is given, assuming that),
$$\Delta S_{surroundings}=\frac{\Delta Q... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/487862",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Friction due to pure rolling on an inclined plane When a body is executing pure rolling we know that the point of contact of the body with the ground is at rest with respect to the ground. If that's the case no friction should act as it is stationary.So when a body is rolling down an inclined plane its point of contact... |
When a body is executing pure rolling we know that the point of contact of the body with the ground is at rest with respect to the ground.
This is true.
If that's the case no friction should act as it is stationary
This is false. Static friction is a friction force that can act on an object that is not sliding rel... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/488195",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Does friction always oppose motion? Recently I had the following misconceptions:
*
*Static friction always opposes the motion of body.
*The force of friction cannot initiate motion in a body.
Now I came to know that my understanding was wrong and that friction indeed can cause motion in bodies, and that static fri... | Friction opposes relative motion between two bodies.
Note that might mean that friction can create motion relative to i.e. you. For example, dropping an item on a moving belt. Friction opposes and reduces the relative motion of the item and belt until they move together. But now they’ve started moving relative to you.... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/488562",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "16",
"answer_count": 5,
"answer_id": 1
} |
What exactly does it mean to say that QED is of "universal strength and form"? In a paper from 1961 (Gauge Theories of Vector Particles, Glashow and Gell-Mann), the authors describe quantum electrodynamics thusly:
"It is of universal strength and form..."
What exactly does it mean to say that it's of "universal" stre... | The answer seems to be the one suggested by Physics_Et_Al (you should really post an answer as an answer; not as a comment. That's the way this is supposed to work).
Here's a quote from Invitation to Contemporary Physics (Ho-Kim, Kumar, Lam):
"By universality, we mean that the coupling to matter is proportional
to... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/488783",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
Reason behind vector addition law What is the reason behind triangle law of vector addition, in other words, how is this really justified?
| Well I finally realized that we are actually not adding two quantities but trying to find the resultant. Therefore the resultant must indeed be the third side of the triangle as it will give us the shortest distance between the two points, i.e the tail of one and the head of another. By definition the resultant is that... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/488889",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 2
} |
How did Einstein know the speed of light was constant? I often hear the story of how Einstein came up to the conclusion that time would slow down the faster you move, because the speed of light has to remain the same.
My question is, how did Einstein know that measuring the speed of light wouldn't be affected by the s... | Einstein was influenced primarily by the electromagnetic theory developed by several people and culminating in the Maxwell equations, and by the experiments on the speed of light in moving water carried out by Fizeau.
At the time it was not common knowledge what light would do in general; the interpretation of the ele... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/489291",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "92",
"answer_count": 6,
"answer_id": 4
} |
How to measure (heat) energy used? Before I start with my question, would like to highlight - the last time I delved into this topic was 13 yrs back during my schooling courses. But the enthusiasm never died.
Coming back to topic - I want to know/understand if there's a way to know the amount of energy (heat energy, i... | As Bob D has commented, this is very difficult to calculate theoretically. He didn't mention that you need to know the thermal conductivity of the egg's contents – and to make things worse, this conductivity will change as the white and yolk change consistency.
Boiling an egg in a saucepan is, of course, a very wastefu... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/489513",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Understanding the definition of tangent basis This question could sound silly but I though a lot about it and I'm not new to physics.
Let's say I have a plane on which I use polar coordinates, it means a point $P$ can be indicated by its coordinates $(r, \theta)$.
Then we need a basis in order to write the vectors as ... | There is nothing a priori about coordinate systems. They have no physical significance and are invented by humans, not by nature.
I recommend that you read Misner, Thorne, and Wheeler’s discussion in Gravitation about how coordinates are like telephone numbers assigned simply to keep track of which events in spacetime ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/489587",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 4,
"answer_id": 1
} |
Do the pure states in the decomposition of a density operator need to be orthonormal to each other? So, I was studying quantum computation using the book Nielsen and Chuang and it stated a theorem known as "Spectral Decomposition theorem"
$$A=\sum _{i}\lambda _{i} | i \rangle \langle i|$$
I infer from this theorem tha... | The vectors $|\psi_i\rangle$ out of which you build the density matrix don't have to be orthornormal. They don't even have to be a basis: you can have more or less of them than your dimension. However, the decomposition theorem tells you that you can always find an orthonormal basis in which the density matrix can be w... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/489733",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 2,
"answer_id": 0
} |
Why is neper frequency called a frequency? In the context of complex frequency of RLC circuits, the real part is called neper frequency, according to units it's understandable that it has 1/s as the unit which is same as frequency but what is repeating at this frequency as I nowhere see any repetition? Why is it a freq... | the neper represents attenuation, or energy loss. the rate of energy loss will then be so many nepers in such an amount of time, or so many nepers per second. As such it "looks" like a frequency (cycles per second) even though it is not oscillating.
Bear in mind though that a more useful and convenient measure of ener... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/489866",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 4,
"answer_id": 0
} |
Magnetic field of rotating wire I was doing some questions on the magnetic field when a charged body is rotated on its general axis, but I had a doubt that what if it's not the general axis but somewhere else. Like, for example, take a ring and take an axis along the diameter of the ring and to find its magnetic field ... | I think that perhaps the best way to solve the general problem of finding the magnetic field of an arbitrary charge distribution rotating over an arbitrary axis is to simply integrate the magnetic field produced by the differential charge elements that make up the charged object, which is:
$$\mathbf{d \vec{B}} =\frac{μ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/489991",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
How is quantum physics translated into the world of electronics? I remember watching a documentary about early works in quantum physics and how it was essential to the microelectronics revolution and the invention of the transistor. What part exactly helped? Is there a source on technical aspects that lead to such deve... | One word: Semiconductors.
Semiconductor physics cannot be explained using classical physics. One needs to understand the electronic band structure of these materials in order to engineer various devices (e.g., p-n junctions, p-n-p junctions etc.) using them. Without such basic devices we won't be able to engineer moder... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/490448",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Does throwing a penny at a train stop the train? If I stand in front of a train and throw a penny at it, the penny will bounce back at me.
For the penny to reverse its direction, at some point its velocity must go to zero. This is the point it hits the train. Two objects in contact have the same velocity, so the train ... | It depends. In principle it could, in any realistic situation it is not even close.
As you said, it comes down to the fundamentals. When you throw a coin at a train, the train will exert some force on the coin via electrostatic repulsion. On the atomic level this is due to the electrons in the coin getting too close to... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/490574",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "80",
"answer_count": 14,
"answer_id": 4
} |
Focus iPhone torch to a beam I would like to focus an iPhone 5s' torch light into a beam with an angle of around 5 degrees or smaller (hopefully). Is this easily doable with a single lens?
I'm hoping to buy a lens and attach it in front of the iPhone (by 3D-printing a custom case). I just don't know which lens I should... | Generating a reasonably collimated beam from an iPhone is only possible if:
*
*You use an enormous lens (several inches in diameter), in which case your beam will be correspondingly enormous.
*You are willing to throw away a lot of the light by using a pinhole positioned on the lamp surface in addition to the lens.... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/490671",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
Can there be interference between a proton and an electron? For example, we know that we can interfere two different electrons or two different protons by employing them in a double-slit experiment.
Now suppose, we mix protons and electrons and shoot them simultaneously for a double -slit experiment. Will the protons ... | The protons and electrons will attract one another by the standard Coulomb force, and this will modify the interference patterns of both types of particle. However a proton wave does not interfere with an electron wave in the sense of wave interference known as superposition. The mathematics of this involves the appara... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/490828",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 2
} |
Newton's third law in magnetic fields Say I have a charged particle moving through a magnetic field perpendicular to it. It will experience a force, but according to Newton third law
Every force has an equal and opposite reaction.
So what is the opposite reaction/force of this magnetic force.
Which body experiences... | A charge may, besides potential energy, experience potential momentum given by $q\vec A$. In the presence of currents therefore the kinetic momentum $mv$ is not conserved, but $mv+q\vec A$ is. The rate of change of this total momentum is equal and opposite for two particles that magnetically interact.
Note that this st... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/490909",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 2
} |
What is temperature on a quantum level? When I was in high school, I learned that temperature is kinetic energy.
When I learned statistical physics, we learned that temperature is a statistical thing, and there was a formula for it.
Questions:
*
*What is temperature in terms of quantum mechanics? This is, how is t... | tl;dr: particles transition been microstates; temperature is a property of the ensemble macrostate at equilibrium
To use a statistics mechanics framing, quantum mechanics describes how particles transition between the different microstates of your system. Temperature is a property that emerges from the macrostate of th... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/491179",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "26",
"answer_count": 6,
"answer_id": 2
} |
Conservation of energy when external force is applied I have heard that an isolated system is where no energy and no mass is exchanged with outside the system. Does that imply that no external force can be applied to an isolated system? Why?
For example, there is a block at rest in a system and an external force is app... | You’re correct that an isolated system is by definition one that cannot exchange mass nor any form of energy with its surroundings.
But a force is not a form of energy. You can apply a force to an isolated system as long as it does no work on the system.
So as long as a force applied to your box does not cause it to mo... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/491525",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
What is probability amplitude and why is it complex? When dealing with Mach-Zender interferometers the professor usually lets $\alpha$ & $\beta$ denote the probability amplitude that a particular photon isn't reflected by the beam splitter and the probability amplitude that a particular photon is reflected by the beam ... | You've answered (1) correctly. A probability amplitude is that thing that you take the square of (well, absolute value squared) to get probability.
That leaves (2), which is essentially the question "why does QM use complex numbers?".
I'm not sure. It's certainly the case that this is just a mathematical choice and co... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/491706",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 2,
"answer_id": 0
} |
Dark matter's effect in 2+1 GR? In the appendix to The Planiverse, it is acknowledged that GR in 2 dimensional space implies no gravitational forces between separated masses--only in the interior of extended massive bodies. The author then speculates that perhaps the natives of the Planiverse will someday discover dark... | The case of lower-dimensional general relativity is an interesting one because due to the symmetries of the Riemann tensor, things simplify quite a lot. In three dimensions in particular, the Riemann tensor has $6$ independent components, which is also the number of components of the Ricci tensor. It can be shown that,... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/491817",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
X-ray imaging of coconut I'm doing the X-ray imaging of a coconut with soft X-rays. But the images have no contrast between the rice and water inside the coconut. How can I adjust the parameters to see this contrast inside the coconut? Horizontal and vertical projection settings for different images (parameters are the... | I should note first that I don't quite understand what exactly you are doing. Are you trying to get images of a whole coconut or of a half coconut? And what does rice have to do with that? Do you just put some rice inside a half coconut?
Nevertheless, let me try to offer some tips to get better contrast. If you cannot ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/492067",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 1,
"answer_id": 0
} |
Time dilation at perceived constant acceleration Let's say that we have a spaceship.
From the beginning, the ship is stationary (relative to me) and not affected by outer forces (like Earth's or Sun's gravity).
Then the ship starts to accelerate at $10\space m/s^2$, that should be comfortable for the astronaut onboard ... | The acceleration measured in the rest frame of the rocket, i.e. by the people on the rocket, is called the proper acceleration. Constant proper acceleration is a standard problem that you'll find treated in all books on relativity, and you'll find a summary of the results in Phil Gibbs' article on the relativistic rock... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/492137",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Why do jet engines sound louder on the ground than inside the aircraft? Everyone is familiar with the whirring sound of jet engines when seeing an aircraft taking off from a nearby airport. It is distinctly very loud on the ground and one can hear it even when the airplane is miles away.
Although one can hear a 'white... | While sound waves can be impacted by the particles in the air to transmit sound, the sound waves can bounce off of the ground much like how you can have a louder or longer lasting sound in an enclosed room as it bounces off walls and such
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/492353",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "20",
"answer_count": 4,
"answer_id": 3
} |
When you fill a bottle with water then liquid nitrogen then turn it upside down, why does it blast off at high speed? I saw in the YouTube video Don't Mix Coke with Liquid Nitrogen! that when you fill a bottle part way with water then pour liquid nitrogen into it then turn it upside down, it blasts off at high speed. W... | I cannot figure out the answer for sure but here's my theory. According to the article Liquid Nitrogen Is Beautiful When It's Dancing Across Gasoline, liquid nitrogen is less dense than water. I'm guessing that means at first, the liquid nitrogen floats on the water. When it's turned upside down, the liquid nitrogen st... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/492620",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
Conduction, convection, radiation: Does evaporation count as one of those? The forms of heat transfer are traditionally described as conduction, convection, and radiation. Is evaporation (or any other change of state) counted as one of those forms? Or is it considered its own distinct form of heat transfer?
| In engineering, heat transfer covers various mechanisms, including thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes (e.g. evaporation).
At a given pressure, different boiling regimes exist depending on temperature (the following image applies to water at a pressure of 1... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/492716",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 0
} |
What is the difference between uniform velocity and constant velocity? I think that uniform velocity implies constant speed but not constant direction. while constant velocity implies constant speed without any changes in direction.
Both tell us that there's no acceleration (since magnitude of velocity is constant).
Th... | The word uniform means the "same in all cases". Therefore, constant and uniform are often used interchangeably. Just be careful about where and when the sentence is used. For instance, if I say a car is accelerating uniformly in the xx-direction, then it has a constant acceleration in that direction.
In the case of a c... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/492797",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 4,
"answer_id": 2
} |
Do we breath less oxygen in Humid air than dry air ? Since the volume of breathing remains same In rainy season, when Air is fully saturated, while we breath do we get less oxygen in than dry air ? Since the volume of breathing remains same?
| You are right that the higher the partial pressure of water vapor is in the air, the lower the partial pressure of the other gasses will be.
But this depends on temperature: when relative humidity is 100 % the partial pressure of water vapor may be lower than at 50 % RH and a higher temperature.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/493298",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 0
} |
Unitary Transformation of an Interfering Beam Splitter I was reading this research paper Quantum interference enables constant time quantum information processing and was confused by one particular expression involving the Hamiltonian of a beam splitter.
We consider two interfering modes $a$ and $b$ on a beam splitter ... | *
*Write the evolution equation in the Heisenberg picture for $a$ (and the same for $b$):
$$
\dot a = i[H,a]\ .
$$
*Simplify the expression for the given Hamiltonian (omitting $\hbar$):
$$
\begin{aligned}
\dot a &= -\tfrac12[a^\dagger b e^{-i\phi},a]+\tfrac12[ab^\dagger e^{i\phi},a]
\\
& = -\tfrac12[a^\dagger,a] b e... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/493524",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Will pyrolytic carbon/graphite repel the Sun's solar wind? Since a moving charged particle has a magnetic field, as well as an electric field, and pyrolytic carbon/graphite repels an external magnetic field, would this mean that an object made out of pyrolytic carbon/graphite will repel the Sun's solar wind since the s... | Of course, solar wind produces a magnetic field and pyrolytic graphite is indeed a diamagnetic material. When the magnetic field exerts a force on the pyrolytic graphite spacecraft, the particles of the solar wind will be deflected by the Lorentz force. Pretty much like what happens in a magnetosphere. It wouldn't prop... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/493622",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
Why pulley systems give mechanical advantage? In a system with 2 pulleys, to lift a x kg object y meters I would need half the force that the object exerts due to gravity but pull the rope double the distance, why does this happen this way?
| This can be viewed as a requirement of the work-energy theorem and the conservation of energy. Assuming you alter the system slowly enough that parts don't gain a significant kinetic energy, the work you do by pulling the rope must be equal to the work done against gravity or any other forces that may be applicable. If... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/493851",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
What is the difference between position, displacement, and distance traveled? Suppose the question is somewhat like this:
If $v=8-4t$ and the position at time $t= 0\ \rm s$ is $2\ \rm m$, find the distance traveled, displacement, and final position at $t=3\ \rm s$
Since $\text dx/\text dt=v=8-4t$, ... | Suppose you start on the 10th step of a very big stair. You walk 100 steps up the stair, then turn around and walk 95 steps down.
*
*Your position is where you are, which is now the 15th step.
*Your displacement is the net change of your position, which is $15-10=5$ steps.
*Your distance traveled is how much you a... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/494096",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 7,
"answer_id": 6
} |
Motion between two particles in a relative manner Suppose a particle A is travelling in east direction with velocity of x m/s and another particle B is travelling with velocity y m/s in the west direction. Why does the the particle B appears to move towards A with a velocity of x+y and not just y m/s?
| As it is already answer by so many but i want to add one more point ,THAT IS -change in distance of B with repect to time will be equal to ym/s if you take your frame of reference as origin according to origin it velocity changes because it s distance with respect to time change equal to y=m/s but now yiu change fram... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/494630",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 4,
"answer_id": 3
} |
Every action has an equal and opposite reaction. Is is true for torques as well? So, we studied in classical mechanics that every action has an equal and opposite reaction. So if we apply a force to some object, that object will exert an equal amount of force on us but in the opposite direction.
Can the same also be s... | A torque is exactly the same as two equal and opposite forces acting at different points on a body.
Each force has an equal and opposite reaction force, and the reaction forces are the same as an equal and opposite torque.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/494712",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 3,
"answer_id": 0
} |
What's wrong with this argument that the potential energy of an arbitrarily heavy object at arbitrary height is $0$? Consider an object with mass such that there is a gravitational force downward of $1N$. Also assume the environment is a perfect vacuum. Now assume that we exert a force of $1+\epsilon $ Newton upward on... | Work done by a force = Force * Distance the object moves.
When the object is initially stationary, that 1N is doing no work, because the object is not moving.
After you apply your (1+ϵ)N force, the object is moving, so when you re-apply your 1N force, you are actually doing work on the object just to keep it moving at ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/495510",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 1
} |
How can we tell if the Earth is spinning without any external references? The rotation of the Earth about its axis makes it bulge at the equator and contract at the poles due to the centrifugal forces. How do we know, without any external references, that the Earth is spinning if there is nothing to compare it to? For ... | Because the Earth is rotating on it-self, it is not an inertial referential, which means that there are additional fictitious forces acting on objects at rest in the frame of reference. For a spinning referential, the fictitious force is called the Coriolis force, which is responsable of many phenomena such as Foucault... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/495614",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "9",
"answer_count": 6,
"answer_id": 2
} |
If Poisson Bracket of Momentum and Position is non-zero, why no Uncertainty Principle? In Hamiltonian classical mechanics, we have that the Poisson bracket of position
and momentum satisfies $$\{q_i, p_j\} = \delta_{ij}$$
But this implies that momentum and position 'generate' changes in each other. I.e. as we move alon... | What one requires for the uncertainty principle to arise is that the relevant observables should not commute, i.e., their commutator is non-zero. The Poisson bracket of two observables is not the same as their commutator. Even if the Poisson bracket of the classical observables is non-zero, they do commute in classical... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/495758",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 1,
"answer_id": 0
} |
Does $\mathcal{M} = AdS_2 \otimes S_2$ makes any sense as a manifold? I'm not a topologist or a group theorist and I need a clarification about some notations.
Consider the Bertotti-Robinson metric in General Relativity (relativity students should study this metric, by the way, it's a really nice one!):
\begin{equation... | It is actually the direct product, not the tensor product (physicists frequently get too sloppy and end up using one or another without acknowledging the difference between the two). It is trivial to show that a direct product of manifolds is a manifold.
Direct product is commutative, so $S_2 \times AdS_2 = AdS_2 \time... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/496053",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
Can force be applied without accelerating? When I push against a wall, I am applying force on the wall and the wall applies an equal force against mine therefore the wall doesn't move and neither does my hand. But isn't acceleration required to apply force? My hand is not accelerating when I am applyin the force. Still... | First of all, F =ma doesn't mean that to apply force you have to have acceleration. F =ma means force F applied on mass m produces an acceleration a and this product of m and a gives the force which was applied. How much force can you apply can only be known when you set some mass on motion, your acceleration doesn't h... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/496138",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 6,
"answer_id": 4
} |
What prevents ice from being an electret? My question is apparently simple: if we put water in a electrostatic field and leave it to freeze, while still in the strong electrostatic field, to make ice, why wouldn't this ice exhibit electret capabilities?
| If I'm understanding your question correctly, then it seems like you're asking why ice is not a ferroelectric material. In classical physics, dipoles interact in such a way that their dipole moments have less energy when they're aligned in opposite directions. This is true for both electric and magnetic dipoles. Theref... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/496390",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 1
} |
Text Recommendation: Random Walks (for physicists) I am an incoming graduate student in Theoretical Physics in the Netherlands, and I would like to know if any of you could recommend texts on random walks with applications to physics. My university offers a course on random-walks but I unfortunately do not have the pre... | Howard Berg's "Random Walks in Biology" (https://press.princeton.edu/titles/112.html) is an excellent, very short, and simple introduction to the topic.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/496542",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
How can I calculate the equivalent resistance of this circuit with resistors in parallel with wires? Problem:
Calculate the equivalent resistance, $R_\text{eq} ,$ of this circuit:
$\hspace{50px}$.
My solution attempt
*
*Тhe $12 \, \Omega$ resistor and the $6\, \Omega$ resistor are in parallel, so$$
R
= {\left(\fr... | We are not supposed to provide solutions to homework and exercise questions, only guidance.
So here is some guidance;
The top circuit diagram below is your top diagram. The bottom diagram is equivalent to the top diagram, as long as all the "wires" shown are considered ideal (that is, zero resistance).
So given the bot... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/496651",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Why is particle physics called high energy physics? The highest energy accelerator till date is the LHC which operates at an energy scale of perhaps 10-100 TeV. In SI units this is about $\sim 10^{-6}-10^{-5}$ Joule which is several orders of magnitude smaller than the energy scales we are used to in daily life. For ex... |
'High' with respect to what?
High with respect to the number of particles involved when they mention the energy value. The TeV energy of particle accelerators is related to the average energy of each accelerated particle.
You are comparing the energy of a single particle with the average energy of a system of particl... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/496792",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
Rutherford/Geiger–Marsden gold foil experiment: what did they really think about alpha particles? Most tellings of the experiment where alpha particles were fired at a thin gold foil point out the following:
*
*atomic model being tested was the plum pudding model: negatively charged particles (electrons) embedded in... | The plum-pudding analogy is only an analogy, and it breaks down when subjected to such close scrutiny. They knew the electrical charges and the masses involved, and the forces produced by those charges, and they did the maths. If the positive charges were spread out through the whole volume of the atom then the alpha p... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/496926",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 2,
"answer_id": 0
} |
What is the difference between a Surface Acoustic Wave (SAW) (Rayleigh Wave) and a Leaky SAW? I have come across leaky SAWs and I'm not sure what the difference is, and why some substrate cuts are listed as leaky SAW design.
Trying to search for diagrams so I could see what the differences maybe, I typically find this ... | Sorry I did not see your post sooner, but this interpretation is incorrect. Leaky SAW devices suffer from radiation of energy into other wave modes within the substrate material - typically slow shear bulk acoustic waves. This leakage can be controlled on certain substrates through control of electrode thicknesses.
See... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/497189",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Why is the necessary energy for a photon to lift an electron higher than the band gap energy? The band gap energy of silicon is around 1 eV and though the required energy for a photon to lift an electron up into the conduction band is around 3.6 eV.
Why is this?
Is the Energy of an absorbed photon exactly the energy of... | Silicon has an indirect band gap. This means that although there is a conduction-band state which is only 1eV above the top of the conduction band it occurs at a different Bloch momentum ${\bf k}$. The nearest state with the samae ${\bf k}$ value is 3.6eV above the top of the valance band. Photons have a wavelength $\a... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/497350",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Can anyone explain the Planck area? First of all, I am not an expert. I was reading about the holographic principle and came across the Planck area. It says that Planck area is the square of Planck length and there were some pictures like this:
source
I know that this Planck area is used for black holes. But doesn't ... | The Planck length is approximately $1.616255\times 10^{-35}$ m. You get the Planck area by squaring that, just like you get the square metre by squaring a metre. So the Planck area is approximately $2.61228\times 10^{-70}\,\mathrm{m}^2$.
As Wikipedia says, we expect geometry to get weird near that scale, so despite you... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/497475",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 5,
"answer_id": 1
} |
What is the mass of photon? I'm sorry if this question is asked before, but I searched through the site and none satisfied me.
In most of the books I've come across, they just write "rest mass of photon is zero." But never talk about the relativistic Mass. Even in other answers on this site they have written exactly th... | The mass of the photon is zero. The end.
Relativistic mass is a hazardous concept, and many authors refuse to use it. It makes the increase in kinetic energy of an object with velocity appear to be connected with some change in the internal structure of the object. See also this question on SE.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/497579",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
How fast does an electron move? I've been reading this website: www.physics.wayne.edu/~apetrov/PHY2140/Lecture8.pdf to learn how fast an electron moves in a circuit.
On page #8, #9 and #10 It says to take the Cross-sectional Area of the wire, The current, The density, The Charge and the electrons^3
Area- ... | It's because of drift velocity of electrons. Though the electromagnetic disturbance propagates at somewhat near the speed of light, the actual velocity with which the electrons move is much lower because of collisions with the ions in the lattice and random thermal motion.
The electrons can't move fast because they are... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/497916",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 1
} |
Difference between left- and right-handed, helicity and chirality What is the difference? I know there is the (almost) same question What's the difference between helicity and chirality? but when a particle is given as left-handed. Is it helicity or chirality?
| Helicity is the projection of spin onto momentum of a particle:
$$ h = \frac{\vec s\cdot \vec p}{|\vec p|} $$
If a particle with spin-1 moves exactly in the same direction as its spin points (let's say the spin point in $z$-direction and it also moves in $z$-direction), then the helicity is $h=+1$. If it moves in the ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/498042",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
Heat reduction based on compression So I was thinking about air conditioner today and how we run air across compressed freon to cool down air but why do we need freon at all why not store just compressed air. My guess is because its inefficient.
My question given a 1 cubic meter tank of air, if the room temperature at... | I will address the use of air rather than freon (or its current replacement) as a refrigerant. I believe @BowlOfRed has satisfactorily answered your other questions.
Air is not used as a refrigerant because it would not be practical. This is because a refrigerator requires the use of a working fluid that can undergo ph... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/498395",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 2
} |
Electrons with disorder & something like AdS/CFT duality I know that consideration of electrons with disorder can be based on Feynman diagrams with disorder lines. In this approach, only non-crossing diagrams are important and give contribution to self-energy function $\Sigma$ and related quantities. Parameter $p_Fl$ p... | I am going to stick my neck out some here, but make this brief so I do not write something wrong. I would say this is a possibility. A quantum spin liquid is a disordered set of quantum spins with long range entanglements. With a topological order in this bulk there may then be edge states with short range entanglement... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/498543",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
Half life of elementary particles Do elementary particles have half life? Can we theoretically calculate half of a particle which is in complete isolation?
| Some elementary particles, such as the electron, are stable; others, like its more massive sibling the muon, are unstable and decay into other particles. A muon decays through the weak interaction into an electron, a muon neutrino, and a electron antineutrino, all of which are elementary. The muon’s half life is 1.56 m... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/498757",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
Solution to Maxwell-Lorentz equations I am trying, without success, to find an example (preferably simple) of solution for the Maxwell-Lorentz equations, i.e., the coupled system of Maxwell equations + dynamics of a charged particle given by Lorentz force. Say we have a (for simplicity, non-relativistic) particle of ma... | May be, one my construct such theories (the only ones I am aware, introduce a charge distribution for the classical particles) , but these are not the Lorentz-Maxwell theory. The whole development of quantum mechanics started from this one and has been developed along his lines to get finally the QED. Any other varia... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/498892",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
In 2D CFTs what are the possible forms of correlation functions I am following Sylvain Ribault's lectures on 2D CFT (https://arxiv.org/abs/1609.09523) in which he lays out 2D CFTs in an axiomatic format.
In a CFT we assert (as an axiom) that there is a correspondence between an algebra of operators $\mathcal{A}$ define... | In my lectures the space of states is not assumed to be a Hilbert space, i.e. to have a positive definite scalar product. Actually it is not assumed to have a scalar product at all. So you cannot write $\langle v|$ and the short answer to your question is no.
Actually you do not need a scalar product for computing OPE... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/499014",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
Bose-Einstein condensation: Bogoliubov Approximation I'm trying to understand the Bogoliubov approximation from "Statistical Mechanics" by Pathria and Beale. First of all they say
Since $a_0^{\dagger}a_0=n_0=O(N)$ and $(a_0a_0^{\dagger}-a_0^{\dagger}a_0)=1<<N$, it follows that $a_0a_0^{\dagger}=(n_0+1)\simeq a_0^{\dag... | Perhaps, it will serve you a fully analized example to get an understanding of this "approximation":
L. Banyai, About the c-number approximation of the Macroscopical Boson Degrees of Freedom within a Solvable Model. phys. stat.sol. (b), 234, 14 (2002)
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/499144",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Is the statement that $U(x)$ is quadratic for simple harmonic motion equally strong as the statement that $F(x)$ is linear? Is the statement
"If the potential energy of a particle under oscillatory motion is directly
proportional to the second power of displacement from the mean
position, the particle performs a ... | If the potential energy is quadratic in the displacement only for small oscillations, then the restoring force is proportional to the (negative) displacement only for small oscillations. So I would not say the second statement is more general. The one statement is exactly true, so is the other. If one is only approxima... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/499574",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 4,
"answer_id": 2
} |
Does the ground state of the Schrödinger equation, in any number of dimensions, always have constant phase? I just read this argument in this paper (PDF).
It suggests that, from variational principles, you can show that you can always lower the energy of a state by making the phase constant, thus resulting in a ground ... | They're not assuming that $\psi$ is a solution of the Schrödinger equation. What they are doing is, given an arbitrary wavefunction $\psi$, calculating its energy expectation value $\langle \psi | H | \psi \rangle$, and seeing how they can tweak $\psi$ to make this lower. Crucially, by "energy" they mean this mean valu... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/499846",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
"Printing" 3D structures using an atom laser? An atom laser is a coherent beam of atoms, similar to a laser. This is formed through use of Bose-Einstein condensate.
Could such a beam be focused and used to deposit atoms on a surface to build up an atomically-precise nanoscale object?
| This can also be done with a normal (optical) laser. It actually won the Nobel prize this year, it's called optical tweezers.
Some cool structures people built 'atom by atom' are Eiffel towers, Moebius strips etc (paper):
With an atom laser, the atoms would be moving so you'd need to somehow stop them before they can ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/499942",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
Pressure in a swim ring I have a work related question and would love a physicist’s perspective.
My problem essentially boils down to whether the pressure is greater on the inner or outer “welding” in a round swimming ring, when it is inflated. My intuition tells me that they are equal, but I can’t explain why. Any adv... | Your intuition is wrong.
If you assume the ring is a membrane (i.e. it if it was not inflated, the material it could not resist bending) the tension at any point depends (inversely) on the curvature of the membrane, which is different on the inside and the outside.
Unfortunately I can't find a simple reference to the... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/500489",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Why people feel outward force in rotor ride? I know centrifugal is fictious force but what is possible reason for the force that people feel in rotor ride outwards.
The reason for people not falling down is friction force which is in vertical direction so, what is the force in horizontal direction that makes people fe... | Suppose you're in a car and stomp on the brakes. If you're not wearing a seat belt you'd describe your motion as "thrown forward," but that's an illusion due to the non-inertial reference frame of the accelerating car. To an observer on the side of the road, you're moving forward with the same velocity you had before,... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/500683",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
As $SL(2,\mathbb{C})$ is a double cover of the Lorentz group, is $SL(2,\mathbb{Z})$ a discrete subgroup of the Lorentz group? The group $SL(2,\mathbb{C})$, the group of $2 \times 2$ complex matrices with determinent $1$, is a double cover of the Lorentz group. (These transformations can be understood as Mobius transfor... | I never considered this issue, but I think the answer is positive if, in your view, a discrete subgroup is a subgroup of a topological group which is made of isolated points.
In fact, the canonical projection $\pi : SL(2, \mathbb{C}) \to SO(3,1)_+$ is a surjective Lie-group morphism which is a local Lie-group isomorph... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/500808",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 3,
"answer_id": 1
} |
Why does carbon nanotubes look "furry" in scanning electron microscopy? In scanning electron microscopy images, carbon nanotubes looks quite different from the schematic hexagonal structured tubes which usually describes them. How come they are all bent and "furry"?
| Because diagrams lie. They have to, in some cases, to make their point clear.
I presume you mean something like this?
(Courtesy "Simetrical", cc-by-sa 3.0. Wikimedia Commons. Retrieved from: 1)
Yes, the tube shown in the picture is artificially straight. It's no different from showing a diagram of, say, an electric wi... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/500927",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Why is Kirchhoff's voltage law true in a DC circuit? If we consider a single electron going around a closed loop, with a battery giving an EMF of $6\ \mathrm V$, why does the electron have to lose the energy in the loop?
If the circuit had zero resistance, wouldn't the electron just gain more and more energy as it loo... | Kirchhoff's circuit laws (both the current law and the voltage law) apply in the lumped circuit approximation only.
That means they apply when the circuit can be accurately modeled as a collection of lumped components whose physical extent is insignificant; connected by ideal wires, with no significant magnetic fields... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/502286",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "6",
"answer_count": 5,
"answer_id": 0
} |
Does the strong force continue to act upon quarks after they fall into the event horizon of a black hole? I'm assuming that when particles come in contact with the event horizon, they start traveling directly to the singularity, which is one point that might need clarification. Tangent particles would obviously act thi... | There are no free quarks in space, they will cross the event horizon still within the hadrons and will keep that way up to the singularity.
Here is, as an example, what a proton really is in terms of quarks:
Whether the tidal force a proton encounters at the singularity is strong enough to turn it into a quark gluon ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/502507",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Electromagnetic wave equation: can we ignore the constant of integration? Suppose we obtain a solution for each of $\mathbf B$, $\mathbf E$ of maxwell equations in the vacuum ($\rho=0$). Clearly, for any constant vector $\mathbf k, \mathbf m$, $\mathbf {B+k}$ and $\mathbf{E+m}$ also satisfy the same set of differential... | We are almost always satisfying Maxwell's equations (or any set of differential equations) with respect to some boundary conditions. Usually we assume that a vector field goes to zero at infinity, which means it is uniquely specified by its divergence and curl. (See the Helmholtz decomposition.) If it doesn't go to zer... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/502645",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
How to derive the angular velocity of circular orbits in Kerr geometry? I am trying to derive the angular velocity of a circular orbit in Kerr geometry, eqn.(2.16) in Bardeen et al (1972) which reads $$\Omega=\dfrac{1}{r^{3/2}+a}$$ (Note that I am using the units in which $M=1$ and only direct orbits are considered i.e... | Another solution for you:
consider a circular (r=const) timelike geodetic in the equatorial plane ($\theta=\pi/2,\dot{\theta}=0)$
if you calculate the geodesic equation for the r coordinate you get:
$$\frac{d}{d\lambda}\frac{\partial \mathcal{L}}{\partial \dot{r}}=\frac{\partial \mathcal{L}}{\partial r}=0\tag 1$$
whe... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/502796",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 1
} |
Is the Earth a gyro? Due to rotation and low friction, can the Earth be considered a gyroscope? If so, any interesting implications to this? Thanks
| The moon’s gravity exerts a torque on the earth, which causes the earth’s axis to precess (as a gyroscope subjected to an off-axis torque does). So the North Star is only approximately above the North Pole currently. In 13000 years, earth’s axis will point somewhere totally different, and in 26000 years or so it will b... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/503159",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 4,
"answer_id": 2
} |
How exactly is white light a combination of several wavelengths? I have read that light is an electromagnetic wave. Every ray of light has a specific wavelength. The colour perceived by any observer is dependent upon the wavelength of the incident light.
What I don't understand is that how do electromagnetic waves of d... | To understand this you need to learn about the fourier transform. It describes how a function of time (in your case the time dependent electric and magnetic field strength) can be decomposed into its constituent frequencies.
To me your question seems similar to asking
"How do vertical and horizontal velocity of an ob... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/503429",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 4,
"answer_id": 2
} |
Will a can filled with vacuum move when we let in air?
This picture is from L.C.Epstein's book Thinking Physics. The upper can is filled with compressed air, and, when an opening is made on the right, the air comes out and the can shoots left. The question is what happens to the lower can, filled with vacuum, when we ... |
*
*Shouldn't the can still start moving from the moment we make the opening and until the air pressure inside the can is equalized with the outside air?
Indeed it will, but that takes very little time.
*If that in fact happens, why would it stop and return ("a momentary slight oscillation about the ce... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/503517",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 2
} |
In the Stern-Gerlach experiment, why is there a nonzero force even though the atoms were electrically neutral I know that the magnetic moment of a particle is given by:
$\vec{\mu} = \frac{gq}{2mc}\vec{S}$
I know that in the Stern-Gerlach experiment, neutral silver atoms were used. Additionally, the deflection in this e... | You're really asking how there can be a magnetic moment $\vec{\mu}$ when the atom has zero charge.
Moments are, in general, about separation. For example, consider two forces that are equal in magnitude and opposite in direction: The net force is zero. But if they're applied at different points, they still provide a... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/504168",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Measurement postulate and black hole information paradox: are they related somehow? The measurement postulate states that whenever we make a quantum measurement, we select (projection) from the general superposition state a single pure state. Thus, as a general quantum state is a mixed state, the measurement postulate ... | I don't see how these two things could be related, since collapse is only a feature of one interpretation of quantum mechanics (Copenhagen), while the black hole information paradox has nothing to do with any particular interpretation of quantum mechanics.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/504316",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Linear perturbations of the energy conservation in FLRW spacetime Recently i have some troubles regarding linear stability analysis in GR, especially matter conservation equation.
First order perturbations of the Hubble parameter and energy density are:
$$H=H_b(1+\delta(t)),\qquad\rho=\rho_b(1+\delta_m(t))$$
Using this... | It looks like, that you are almost there. You just have to use the background equation of motion to cancel the remaining terms, ie.
$$\delta_m\left[\dot{\rho}_b+3H_b(1+\omega)\rho_b\right]=0$$
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/504448",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Why the ground state energy of bosons are 0 at T=0K ? Does it violate Heisenberg's Uncertainity Principle at 0K? Bosons obey Heisenberg's Uncertainity Principle but do not Pauli's Exclusion Principle. That's why in Bose Condensation we get a large amount of particles in a single state i.e. ground state at T=0K. But why... | Bose-Einstein Condensates (BEC) do not violate the Heisenberg's uncertainty principle.
Traps
Usually, BECs are not in free space, but spatially confined by some potential $V(r)$. The total Hamiltonian is $H = p^2/2m + V(r)$ so your "$E=0 \rightarrow p=0$" reasoning does not hold.
This potential $V$ is usually approxim... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/504531",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
Is a state with no fluctuations in particle density necessarily a stationary state of the Hamiltonian? Consider a system of identical particles (bosons or fermions) with field operator $\hat{\psi}(x)$. The particle density operator is $\hat{\psi}^\dagger(x)\hat{\psi}(x)$.
Suppose that the particle density is constant e... | Does $\langle \psi | \hat{x} | \psi\rangle = c$ mean that $\hat{x} | \psi \rangle = c | \psi \rangle$?
In case of free particles, QFT Hamiltonian:
$$
H = \int \frac{d^3p}{(2 \pi)^3} \; \sqrt{p^2 + m^2} a^\dagger_\vec{p} a_\vec{p}
$$
is not even proportional to the particle density.
So the state with mean particle densi... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/504993",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 1,
"answer_id": 0
} |
Anticommutation relations for fermionic fields imply that Hamiltonian / Lagrangian can at most be linear? Fermionic field operators do obey anticommutation relations, so for a chosen Field operator (and the field momentum), we have:
$$
\{\Psi_a, \Psi_b\} = \{\pi_a, \pi_b\}= 0
$$
with the $\Psi_a$ being different fiel... | *
*No, if there are more than one Grassmann-variable (which is often the case), the Lagrangian/Hamiltonian can contain non-linear higher-order terms. With $n$ Grassmann-variables, one can build an $n$th-order polyonomial.
*In field theory (where the number of DOF is infinite), one can in principle construct higher-o... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/505180",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Notion of Present Can't I sync all watches in spacetime and call this time slice the present? In Carlo Rovelli's book he tried to explain that the notion of the present is local only, which I could not follow.
| The notion of 'the present' presupposes a notion of simultaniety and Einstein pretty much deconstructed this notion in his paper on special relativity when he promoted the constancy of the speed of light to a universal principle. This deconstruction is pushed even further when he developed his theory of General Relativ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/505506",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 4,
"answer_id": 3
} |
To which magnetic pole would a positive charge entering from space move to? Does the charge of an ion, be it negative or positive, have an effect on which pole it will move towards on Earth, or will the charge only determine the helical motion (clockwise or anticlockwise) rotation of the said charge? What connection is... | A charge is not attracted to magnetic poles. Rather, a magnetic field induces a force on a moving charge in a direction perpendicular to both the velocity of the charge and the direction of the magnetic field.
However, a charge whose velocity has a component parallel to the magnetic field will tend to spiral along t... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/505907",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Will creep occur if a metal is subject to equal stress from all sides? Aluminium creeps at a temperature range of 200 to 300 degree Celsius.
But if the entire bulk of the metal is at a uniform temperature, say, 0 degree Celsius, and no external stress of any kind is given, will creep still occur ?
Or will the creep be ... | If a specimen of metal were subjected to hydrostatic stress it would creep indeed: the volume would change, while the "shape" would not (no deviatoric strain).
Most theories in continuum mechanics would de-couple deviatoric and hydrostatic creep behaviour, as the latter occurs often on longer timescales and is less pro... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/506208",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Damped Oscillation and Period In my school experiment, I wanted to measure the gravitational constant ($9.81 \ m/s^2$) by using a pendulum. If we take into account the damped oscillation (i.e. friction forces), does that affect the period?
As far as I know, the position $x$ of a particle undergoing Simple Harmonic Moti... | Yes, damping forces like friction and drag force affects period in way :
$$ T = {2\pi } \left( \sqrt{\frac{k}{m} - \left(\dfrac{b}{2m}\right)^{2}} ~\right)^{-1} $$
Where $b$ is damping coefficient.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/506332",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 1
} |
Why is work equal to force times displacement? This is how I think of what work is.I am sure I am wrong somewhere because I shouldn't be coming to the conclusion that I am coming to.It would be helpful if you would point out where this conceptual misunderstanding is.
Work is just change in the energy of an object.The o... | If you apply a force F to something initially at rest, and keep the force going over a distance D, the force accelerates the thing to a speed V where VV=2FD/M.
In other words the velocity of the body doesn't rise in proportion to FD, but the velocity squared does.
If you rearrange the last expression you get mVV/2=FD. ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/506489",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 9,
"answer_id": 5
} |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.