Q stringlengths 18 13.7k | A stringlengths 1 16.1k | meta dict |
|---|---|---|
Will a plastic feel less heavy when I put it in a bucket of water and carry it? If I'm carrying a bucket of water in one hand and a piece of plastic in the other, and then I decide to keep the plastic in the bucket of water (it floats). Will it feel less heavy in the second case?
I think it will feel the same because i... | I don't think you will feel less however the plastic (if could sense ) will of course feel less weight .
Let me explain.
Since the liquid applies buoyant force on the plastic (say $F_b$ ) so by Newton's third law the plastic also applies a force $ F_b$ on it in the downward direction . So the forces acting on the liqu... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/578995",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "9",
"answer_count": 7,
"answer_id": 3
} |
Deriving ideal gas law from Boyle and Charles My textbook states
Notice that since $PV = \text{constant}$ and $\frac{V}{T} = \text{constant}$ for a given
quantity of gas, then $\frac{PV}{T}$ should also be a constant.
I tried to prove this, but no success:
$$PV = a$$
$$\frac{V}{T} = b$$
$$\frac{PV^2}{T} = ab$$
$$PT... | $PV$ is constant for fixed $T$, and $V/T$ is constant for fixed $P$. Hence
$PV=f(T)$ and $V/T=g(P)$.
From these we can write
$V=f(T)/P=T\times g(P)$.
This implies that
$f(T)=kT$ and $g(P)=k/P$ for some constant $k$.
Hence $PV/T = k$ (constant, actually $nR$) is the required answer.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/579140",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 4,
"answer_id": 0
} |
How do forces 'know' they need to move when a system is in motion? I am curious as to how forces move when a system is in motion. This was never fully explained in my physics classes at university. Let me explain:
I understand the Newtonian (classical) physics that there are equal and opposite forces in play. So when ... | Long story short, the upward force is electromagnetic repulsion from the molecules of the floor. As soon as you raised your leg, you removed it from the floor molecule lattice, so it was not close enough any longer to feel a strong repulsion, like before.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/579261",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "9",
"answer_count": 10,
"answer_id": 9
} |
When do two massed exert the same centripetal on a point? I was reading the mark scheme for 2020 Cambridge A-level physics when I came across a question that reads
The stars S1 and S2 rotate with the same angular velocity ωabout a point P, as illustrated in Fig. 1.2.
Point P is at a distance xfrom the centre of star S ... | By Newton's third law, the magnitude of the gravitational forces on each mass must be the same.
"Centripetal" is just a direction indicator, just like how "horizontal" and "vertical" also indicate directions. Since gravity acts in a line between the bodies, and because the center of rotation lies on this line, the grav... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/579325",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Amplitude of superposition states I have a question about the following chart (for 3 and 4 particles case):
What does $P_{cycl}$ mean? How's that relevant to the amplitude of superposition states and their symmetricity?
| *
*The states given in your table seem to be states of a system of N spins in the $\hat{S}^z_{\text{tot}}$ and $\hat{S}^2_{\text{tot}}$ basis which are also eigenstates of the cyclic permutation operator $\hat{P}_{\text{cycl}}$ with $P_{\text{cycl}}$ being the eigenvalue of the cyclic permutation operator.
*An Examp... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/579429",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Is it possible to bend light without changing its color? It seems to me that whenever you change the direction of a wave it also affects frequency. Would this not also be true of light waves bending from, for example, gravity?
| The frequency of light "in transit" isn't well defined in special or general relativity. You can only define frequency shift for light that travels from an emitter to a receiver, and you get a single frequency ratio for the whole trip; it can't be attributed to any particular part of the trip.
In the case of the bendin... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/579543",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 4,
"answer_id": 2
} |
Do "almost black holes" exist? The only things I read about so far in astrophysics are either black holes, developing black holes or not black holes at all.
So I am wondering, is it physically possible to have an object that is almost a black hole, but not a black hole. What I mean by that, is an object that would have... | Neutron stars
(The question is written informally, so my answer is. "For simplicity" <smirk>)
Neutron stars are massive, incredibly dense, hence have very strong gravity; but not so strong that light cannot escape. It has no "event horizon"; but you wouldn't want to be near it.
Related: Quark star (a hypothetical type ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/579737",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "73",
"answer_count": 2,
"answer_id": 0
} |
How much energy is transferred to a human hit by lightning? Wikipedia tells me that a bolt of lightning releases roughly 1 GJ of energy, but I'm guessing that's along the entire length of the bolt and that most of it is dissipated as heat and light to the surrounding atmosphere.
Don't know much about the physics behind... | When lightning is fatal, it is usually due to an electrical discharge-induced heart attack. Since lightning is essentially a electrostatic discharge event, we can roughly view it as analogous to a capacitive discharge.
IEC 60470-1 provides threshold values of various physiological effects of capacitive discharge curren... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/579852",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
Does work done on a spring = elastic potential energy? So the UK exam board specifications (AQA GCSE) clearly state
"...the work done on the spring and the elastic potential energy stored are equal"
Here's my problem,
So work done = Force x displacement
Force = Spring constant x extension
Elastic potential energy = 0.5... | Work is not "force times displacement". Work is an integral $$W=\int\mathbf F\cdot \text d\mathbf x$$
which becomes $W=Fx$ under certain conditions.
The work done by a conservative force is always equal to the negative change in potential energy associated with that force:
$$W_\text{cons}=\int\mathbf F\cdot\text d\math... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/579993",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
Is it okay to for the integrand and bounds of integration to be functions of the same variable? For the sake of simplicity, say we given that $a = 6t$ and that we must find the velocity as a function of time. We would set up the following integral:
$$\displaystyle \int_{v(t_0)}^{v(t)}dv = \int_{t_0}^t 6t\,dt$$
Having $... | Very bad mathematical grammar. It's perhaps comprehensible, but can lead to horrible errors. Don't do it!
Write
$$
\int_0^t 6 \tau\, d \tau.
$$
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/580115",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Are humans special in that they collapse wave functions? First of all, I don't really believe that humans are special. So I know the answer must be that they are not.
But the way quantum mechanics is described is that all particles exist as clouds when humans are not looking but exist as particles when humans look at t... |
that all particles exist as clouds
This is a miss-representation of the mathematics that describes quantum mechanically elementary particles and their composites.
Look at the orbitals of the hydrogen atom:
If one is not careful to understand the postulates and mathematics of quantum mechanics one ends up with partic... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/580444",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 2,
"answer_id": 0
} |
When is a quantum state pure and when mixed? Every definition of the two is always very abstract to me. Like, A pure state is located on the surface of the bloch sphere while the mixed state is somewhere within.
First of all, what is an intuitively definition?
And second of all, how do you practically recognize whether... | A quantum state is pure if you know as much as one can know about a quantum state.
A quantum state is mixed if you could know more about, that is, you don't know as much as is allowed to know about a quantum state by the laws of quantum mechanics.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/580704",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Contradiction in Faraday's law and Motional EMF Consider two parallel conducting frictionless rails in a gravity free rails parallel to x axis. A movable conductor PQ( y direction) of length $l$ slides on those rails. The rails are also connected by a fixed wire AB with a resistor of resistance $R$. Suppose a magnetic ... |
According to the flux approach,
Φ=2
This step is incorrect. If I take any dx element at a distance x from the AB, then area of element is $ldx$ and magnetic field $$B=cx\tag1$$.
Then Flux $\phi$ is given by:
$$d\phi = B dA = cx l dx$$
Integrating the expression:
$$=>\phi = \int cl xdx$$from x=0 to x=x, we get:
$$\... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/580845",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Squares of operators in QM Let $\vec{p} = p_x \hat{x} + p_y \hat{y} + p_z \hat{z}$, and also use the notation $|\vec{p}| = p$, where $p^2 = p_x^2 + p_y^2 + p_z^2$.
What is the difference between the operator $\hat{p}^2 = \hat{\vec{p}} \cdot \hat{\vec{p}}$, and the operator
$\widehat{p^2}$? And which one is the operator... |
What is the difference between the operator $\hat{p}^2$, and the operator $\widehat{p^2}$?
For the sake of clarity let me call your operator $\widehat{P^2}$ as $\hat{M}$ (and let us first work with one dimension). Then by your definition (as stated in the comments), $$\hat{M}\vert\psi\rangle = p^2 \vert\psi\rangle,$$... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/580990",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
How is the spin of hurricanes explained from an inertial frame? I have read that hurricanes spin because of the Coriolis effect. Since the Coriolis force is a ficticious force, which is only present in a frame that is rotating w.r.t. to an inertial one, I am wondering if an inertial observer would have an explanation w... | In an inertial frame the still (relative to the ground) air at the equator is moving very rapidly to the east and the still air at the poles is stationary with still air in between moving at some intermediate speed to the east.
In the northern hemisphere air moving to the north is going from a region of fast eastward m... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/581217",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
Why is the vibrational kinetic energy of a body ignored when calculating the total kinetic energy? In calculating the total kinetic energy of a macroscopic rigid body, we add the total translational kinetic energy and the total rotational kinetic energy of the constituent particles. Why is the total vibrational kinetic... | A net force or torque on a rigid body will not affect its internal energy. As it remains constant before and after the application of the force/torque, it is not relevant to the equations of motion.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/581309",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 0
} |
Can alpha, beta or gamma particles induce fission? Nuclear weapons and reactors get their chain reactions underway via neutron radiation, but do other radiation particles ever contribute?
| Gamma initiated fission is well known, being studied from the very beginning of nuclear physics (lots of work using photofission to understand energy levels in light nuclei) . A little-known feature of the Evaluated Nuclear Data Files is that it has evaluated cross sections for gammas as well as for neutrons. I use the... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/581900",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 1,
"answer_id": 0
} |
What's exactly the new definition of kilogram, second and meter? Could one explain this?
Technically a kilogram (kg) is now defined:
[…] by taking the fixed numerical value of the Planck constant h to be 6.626 070 15 × 10–34 when expressed in the unit J s, which is equal to kg m2 s–1, where the metre and the second a... | The definitions of "second" and "metre" have not changed.
One second is defined in terms of frequency. Frequency is measured in hertz $(1\ \rm Hz=1\ s^{-1}$
We take an atom of $\rm Cs$. And then, we count the frequency of its spectrum. We extract the unit "1 second" from there.
As for the meter, we set that "one metre ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/582193",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "11",
"answer_count": 3,
"answer_id": 0
} |
Proof of a uniqueness theorem in electrostatics I am trying to understand problem 3.4 in Griffiths' Introduction to Electrodynamics:
Prove that the field is uniquely determined when the charge density is given and the potential $V$ is specified on each boundary surface. Do not assume the boundaries are conductors, or ... | Below is an attempt to convince myself (and sorry I literally don't know how to use latex without the physics package).
Here is a link to the Overleaf document
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/582456",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
4-dimensional Fourier transform of $(k\cdot v)^{-1}$ I have been trying to compute, without much success, the following Fourier transform in 4-dimensional Minkowski space
$$
I=\frac{1}{(2\pi)^4}\int d^4 k \,\frac{e^{ik\cdot x}}{k\cdot v},
$$
where $v^\mu$ is any constant vector. $v^\mu$ would be spacelike in my case, i... | If $v$ is spacelike, choose the $k$ axes so that $v$ has only a $z$ component, so that the integral written out explicitly is
$$\begin{aligned}
I &= \frac{1}{(2\pi)^4} \int dk^t\, dk^x\, dk^y\, dk^z\, \frac{e^{i(k^t t - k^x x - k^y y - k^z z)}}{-k^z v} \\
&= -\frac{1}{2\pi v} \delta(t) \delta(x) \delta(y) \int dk^z\, ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/582525",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Electromagnetic field in the Casimir effect So, I read, that the Casimir effect arises from the ground state of the electromagnetic field. But I don't understand where the electromagnetic field in the Casimir effect comes from, since we are considering neutral metallic plates.
| The Casimir force has a mystique that it doesn't deserve. It's just an ordinary electromagnetic force between charged particles.
If the plates were made of uncharged particles, there would be no Casimir force. But metals are made of charged electrons and nuclei. At large distances the electromagnetic field of the posit... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/582708",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
How does information of the parent neutron star get encoded on the event horizon of a black hole? I was watching a video on a typical black hole formation from a neutron star and it suggested that the event horizon appears instantaneously at the surface of the star even as the stellar matter inside starts to converge i... | Let me begin to state that the neutron star must have a mass of at least 1,43 times the Solar mass to form a black hole. When the neutron star starts to contract it will become a quark star, which contracts further. So the event horizon can never be formed at the surface of the neutron star.
The radius of the event hor... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/583112",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 2
} |
What if Jupiter or the Sun was made of rock, like Earth and Mars, rather than gas? Jupiter is a "gas giant". If it was (significantly) bigger the pressure from gravitation would ignite a fusion process and it would become a star, which is basically what happened to the sun.
However, what if a body the size of Jupiter o... | As far as I understand, rocky planets can only grow up to a certain size. This has to do with planetary formation period. A planet cannot grow indefinitely. It can grow only as long as there are particles around the star that can contribute to its increase of mass. During the formation period, dust particles collide an... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/583331",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 0
} |
In what case can we describe forces by potential? Let's consider a particle in an $N$-dimensional space and let's assume that acceleration of this particle depends on its position. So, one can say that we have an $N$-dimensional vector field in an $N$-dimensional space (a mapping from position to acceleration)
What all... | If a force ${\bf F}=\sum_{i=1}^N F_{i}({\bf x})\mathrm{d}x^i$ is given as a co-vector field/1-form on an $N$-dimensional manifold, then Poincare Lemma states that there exists locally a potential $V({\bf x})$ such ${\bf F}=-\mathrm{d}V$ if and only if the 1-form ${\bf F}$ is closed $\mathrm{d}{\bf F}=0$.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/583425",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Sand leaking out of bag and skater "A person skating on a frictionless icy surface is holding a sandbag. The sandbag has a small hole at the bottom, from which the sand starts to leak. As the sand leaks from the sandbag, the speed of the skater..."
The answer was that the speed of the skater stays the same. I thought t... | So what you have done is proceeded with "momentum is always conserved. So $m_i v_i = m_f v_f$ so that $v_f = \frac{m_i}{m_f} v_i$. If you know what the ratio $\frac{m_i}{m_f}$ is, this should answer your question.
But
The net force on skater-bag system is zero. You originally proceeded to apply momentum conservation a... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/583709",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 4,
"answer_id": 1
} |
Does the oscillating electric and magnetic field of a photon generate gravitational waves? From my understanding, little as it may be, because photons have energy they warp spacetime. The energy is expressed as an oscillating electric and magnetic field. Would this mean that the energy is also oscillating and would gen... | Photons are massless and you need massive particles to generate gravitational waves. So clearly it cannot generate gravitational wave. We need massive particles for gravitational waves as, gravitational waves are periodic oscillation of the spacetime framework. Only massive particles can create curvature in spacetime a... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/583785",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "5",
"answer_count": 3,
"answer_id": 2
} |
How does radiation transfer of heat fit in with the Clausius statement of second law of thermodynamics? The Clausius statement of the second law of thermodynamics says that heat flows from a hotter body to a colder body. Heat can flow in many different mechanisms. In the mechanism of radiation for transferring heat, th... | Clausius's differential inequality $dS\ge \frac{\delta Q}{T}$ can also be written as an inequality between rates as follows
$$\frac{dS}{dt} = \dot S \ge \oint_{\partial \mathcal B} \frac{\dot q}{T} dA \tag{1}\label{1}.$$
In $\eqref{1}$ $\mathcal B$ is the body of the system receiving heat through its boundary $\partial... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/583841",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
Is a Lagrangian term $L_{kin}=(\partial^{\mu}\phi^{*})(\partial_{\mu}\phi)$ equivalent to $L_{kin}=\phi^{*}\partial^{\mu}\partial_{\mu}\phi$? In looking at the Lagrangian of a (free for simplicity) complex scalar field $\phi$, we have a kinetic term that goes like:
$$L_{kin}=(\partial^{\mu}\phi^{*})(\partial_{\mu}\phi)... | Almost, you're off by a minus sign, but otherwise yes. You're supposed to use (higher-dimensional) integration by parts on the action
$$
S = - \int_{\Omega} d^4 x\ \big( \partial^\mu \phi^\ast(x) \big) \big( \partial_{\mu} \phi(x) \big) = - \int_{\partial \Omega} d^3 \Sigma\ \phi^\ast(x) n^{\mu} \partial_{\mu} \phi(x)... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/583933",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Why is each wavelength of light diffracted differently?
Why is do we see different colors, instead of white spots like in the middle?
Why is the single slit less intense the further away from the middle you look?
| This occurs because the wavelengths are different for different colours, using the relation between diffraction strength as $S=S(h/\lambda)$ ($h$ is slit size and $\lambda$ is wavelenght), it is apparent that when you keep the slit size constant and compare the different wavelengths then diffraction strength changes so... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/584045",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Is there any physical interpretation of the constant which is seen in the constraint curve of an adiabatic process? What is the $C$ in $ PV^{\gamma} = C$? I always saw it as a result out of the mathematical calculations that we do but I recently saw this video which made me think that the constant may have more meaning... | $C$ is a constant. It simply means that the relationship on the left between pressure, volume and the ratio of specific heats of constant pressure and volume yields the same number at any equilibrium state during the process. The physical interpretation in the case of this process is that it is a reversible adiabatic (... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/584127",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 1
} |
If objects in motion experience time differently, how does my body stay synced when I move my legs or arms? If I move my swing my arm really fast, the matter in my arm should experience time slower than the matter in my body.
So how does my body still sync with each other?
And a more general question that derives from ... |
how does anything ever stay synced ?
Not sure what you mean by "stay synced". Different parts of your body maintain their structural integrity at the atomic level because of the electromagnetic forces between atoms and molecules. This simply involves the exchange of photons (the force carrier for the electromagnetic ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/584228",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "17",
"answer_count": 12,
"answer_id": 8
} |
Why don't we calculate spin number in classical mechanics? We all know classical mechanics deal with bigger objects and
quantum mechanics deal with very tiny particles.
I hear spin number in quantum mechanics, but I don't see anything
like that in classic mechanics.
Why don't we calculate spin number in classical mecha... | Loosely speaking:
Classical mechanics is the approximation of quantum mechanics
in the limit of $\hbar \to 0$ (where $\hbar$ is Planck's constant).
In quantum mechanics the electron's spin is given by
$$\vec{S}=\frac{1}{2}\hbar\vec{\sigma}.$$
where $\sigma_x$, $\sigma_y$, $\sigma_z$ are the Pauli matrices.
The classica... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/584295",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Symmetry for dipole conservation in field theory In article The Fracton Gauge Principle complex scalar field is considered.
There's statement, that for conservation of charge one needs usual U(1) global symmetry:
$$
\phi \to e^{i\alpha}\phi \Rightarrow Q =\int d^Dx \rho
$$
For conservation of dipole moment:
$$
\phi \to... | I think the right way to think about it is to first ask what the symmetry
$$
\phi \longrightarrow e^{i\theta} \phi
$$
means. The actual Unitary operator acting on the many-body Hilbert space that corresponds to this transformation is
$$
U(\theta) = \exp\left( i\theta \sum_r \phi^\dagger_r \phi_r \right)
$$
It is easy t... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/584409",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 1
} |
Why is kinetic friction present when two objects are slipping across each other my mechanics sir was telling us the other day that when the relative velocity is zero between the surface and the object then the object starts sliding, eg in rolling motion without slipping, the v rel is zero at the bottom most point .how ... | When you send a bowling ball down the alley, it starts by sliding. The kinetic friction force (predicted by the coefficient of kinetic friction) on the bottom of the ball produces a torque which causes an angular acceleration. When the backward tangential velocity of the bottom of the ball (measured relative to the ce... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/584526",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Antiproton synthesis For a pion minus hitting a stationary proton, what are the other particles if an antiproton is to be created among them? A positive pion is possible but the total rest mass energy of the final state is comparable to the initial particles.
| I'm not sure you have spelled out the conditions of your problem.
Does
$$
\pi^- + p \to n + \bar p + p ,
$$
that is,
$$
d\bar u + uud \to ddu +\bar u \bar u \bar d + uud
$$
meet them? To conserve baryon number, this is your most economical option.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/584627",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
Can the universe ever contract? I am currently going through this answer related to the Big Bang theory and from there a question arose in my mind:
*
*Can the universe ever contract?
*Can it ever contract to singularity?
I wonder, if it is possible, how it would happen? Is there any chance at all?
I am unaware abou... | Whether it will or it won't, we don't know for sure. Unless we understand the dark energy and dark matter, only time will tell.
It was one of the earlier theories but current evidence seems to suggest that won't be the case. According to the most prominent contemporary physicists, everything in the universe will spread... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/584818",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 2,
"answer_id": 1
} |
Why is there a need for the concept of energy if we have the concept of momentum? We have two concepts that are energy and momentum. To me, momentum is more fundamental than energy and I think that momentum was the thing which we wanted to discover as energy.
Now momentum can describe several things that that energy do... | Here is a thought experiment that should convince you that it's necessary to consider energy and not just momentum. Suppose you stand on a train track in between two identical trains traveling at the same speed. One of them approaches you from your left, and the other from your right. The trains are moving in such a wa... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/585384",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "11",
"answer_count": 12,
"answer_id": 1
} |
What does it mean for particles to "be" the irreducible unitary representations of the Poincare group? I am studying QFT. My question is as the title says. I have read Weinberg and Schwartz about this topic and I am still confused. I do understand the meanings of the words "Poincaré group", "representation", "unitary",... | Irreducible representations of the Poincare group are the smallest subspaces that are closed under the action of the Poincare group, which includes boosts, rotations, and translations. The point is that we should interpret these subspaces as the set of possible states of a particle. For example, if you start with a sta... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/585475",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "27",
"answer_count": 3,
"answer_id": 1
} |
Computing a quality factor of multiple measurements Suppose I measure the same quantity twice with two methods, first I get 0 with 0.001 uncertainty, then I get 1 with 0.000001 uncertainty. We can see from this most likely there is something wrong with the uncertainties or measurements. I am faced with such a problem, ... | Measurements that use the same method can be assumed to have the same systematic error, affecting all measurements equally. So you can, for example, take an average value of these measurements or discuss the consistency of different measurements without knowing the systematic error.
However, it is not possible to compa... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/585565",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Why two orbitals having same phase is not a random phenomenon? I have been reading about Molecular Orbital Theory for Chemistry.
*
*I tend to believe that when two Hydrogen atoms approach each other, whether the $1s$ orbitals are in-phase or out-phase is a random phenomenon. However I know that this is not so. Please... | I have been going through several articles on the matter. Based on that, I have found that the Linear Combination of Atomic Orbitals is a mathematical model with little correlation to the actual process of formation of Molecular Orbitals. Hence the concept of phase/sign of atomic orbitals are simply for the process of ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/585648",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Are wormholes evidence for traversal of a higher dimension? Warning, pop science coming.. please correct what I’m getting wrong. Einstein’s equations of relativity showed the potential for existence of wormholes that can connect different points in space time. I understand the mechanisms for their practical implement... | Wormholes in GR do not require higher dimensions. It easier to imagine curved spacetime as being embedded in higher dimensions, but the usual mathematical description of curved spaces does not require that.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/586941",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "7",
"answer_count": 4,
"answer_id": 3
} |
Direct and in-direct measurments I have seen and heard this many times that a certain (physical) measurement is "direct" or "indirect". What is the characteristic or definition that sharply separates these two notions?
| I'm guessing a direct measurement is one you would read directly from your measuring instrument, like a weight on a scale or the size of an object read from a tape measure. An indirect measurement might require a calculation, like the mass of a planet from the orbital period of a moon.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/587038",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 0
} |
About parallel and intersecting timelike worldlines Suppose that two straight timelike worldlines are (not) parallel with respect to some frame $S$. Will these worldlines remain (not) parallel with respect to any other system $S^{\prime}$ related to $S$ by some Lorentz transformation? Whatever the answer, how can this ... | Two parallel lines must always remain parallel. Let us say two objects are stationary in some reference frame at $x_{0}$ and $x_{1}$, then performing a Lorentz transformation to a primed frame with velocity $\beta$ yields $x'_{0} = \gamma x_{0} - \gamma \beta t$ and $x'_{1} = \gamma x_{1} - \gamma \beta t$.
Further, si... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/587128",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Am I understanding the concept of rotations correctly? Consider a ball placed at distance $r$ from an origin point $O$ on a horizontal plane and remains stationary.
*
*When the ball is viewed from a coordinate system which is rotating
anticlockwise about $O$ with an angular velocity $\Omega$ , what is
the apparent mo... | *
*The vector as an abstract object which points from the origin to the ball is independent of the coordinate system and remains constant in time. However, the coordinates of the vector do depend on the coordinate system and thus are not constant if the basis vectors are not constant.
*Exactly!
*Nope, you have the... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/587247",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Generalized Pauli matrices I wanna know the generalized form of Pauli matrices, for example for $3\times 3$. And do they satisfy all of the properties of Pauli $2\times 2$ matrices?
I wrote $3\times 3$ but I couldn’t write all Hermitian $3\times 3$ matrices with those.
| Pauli matrices (plus the identity matrix) are just a choice of matrices that allow decomposition of an arbitrary 2-by-2 matrix - i.e. a matrix with 4 independent parameters. One could choose them differently, so this particular choice is more due to the tradition and the fact that all the three matrices are already Her... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/587360",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 1
} |
The derivative of the unit velocity vector
The set up:
An intertial frame Y-X used to describes trajectory of an insect on some rigid body using some relative vectors. Symbols: $ \vec{r_a}$ is is the vector connecting the origin to some point on the rigid body, $ \vec{r_b} $ is the vector connecting origin to the ins... | Since $\hat{v}_{rel}$ is a unit vector $\dot{\hat{v}}_{rel} = \vec{\omega} \times \hat{v}_{rel}$. Multiplying by $|\vec{v}_{rel}|$ on both sides gives you that equation.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/587497",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 0
} |
Superfluid Stiffness Definition I am currently reading S. Sachdevs Book on Quantum Phase Transitions focusing on the Bose-Hubbard Model (Chapter 9) and especially the Dilute-Boson Field Theory (Chapter 16).
When describing the fluid phase of the one dimensional model Sachdev says that this phase has quasi-long range or... | There are probably different conventions that lead to definitions that differ by some numerical factor or factors of the mass density, but essentially the superfluid stiffness is the coefficient $\alpha$ in the expressions for the energy density
$$
E[\theta]= \int d^3 x\frac 12 \alpha |\nabla \theta|^2,
$$
where $\th... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/587712",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 1,
"answer_id": 0
} |
Interpretation of normal modes from the mathematical formula In the topic of small oscillations, the system below has a normal mode described by:
$$n_{1} = \frac{x1+x2}{2}.$$
This normal mode is represented as the symmetric mode:
In that case, the center of mass moves as a simple harmonic oscillator. However, the pic... | I) Equations of motion
Kinetic energy :
$$T=\frac{m}{2}\left(\dot{x}^2_1+\dot{x}_2^2\right)$$
Potential energy
$$U=\frac{k}{2}\left(x_1^2+(x_2-x_1)^2+x_2^2\right)$$
with Euler Langrage you get:
$${\ddot x}_{{1}}+{\frac {2\,kx_{{1}}-kx_{{2}}}{m}}=0\tag 1$$
$${\ddot x}_{{2}}+{\frac {2\,kx_{{2}}-kx_{{1}}}{m}}=0\tag 2$$
II... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/587871",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
How we feel (perceive) exact size of object through our eyes? Light after getting reflected from objects gets focused on retina by our lens. The images formed on retina is small, which is then sensed by our brain and depending on distance we feel size of that object.
If an object is at particular distance from us, the ... | As R.W. Bird said, our 2 eyes give us a perception of distance for not too far objects. Our brain uses that information and the apparent size to estimate the real size.
But it doesn't work for distant objects. The moon and the sun have almost the same (apparent) size. When guided only by perception, we are completely u... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/587964",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Heating cup in microwave? I heated my milk cup in the microwave today and noticed that the cup was hot but not the handle. Even if I heat it too much , cups handle temperature remains the same. How is that possible?
| It's probably because your milk cup is made of a material that is a relatively good thermal insulator.
First of all, the microwaves directly heat the milk, and not the cup, as long as the cup is made of material that microwaves pass through without being absorbed.
The heated milk, in turn, being in contact with the sid... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/588033",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "8",
"answer_count": 2,
"answer_id": 1
} |
Cross section in Coulomb scattering of relativistic electrons i'm currently reading about electron scattering and i cant understand the following statement of the book im reading. I quote the book(translated by me):
Many scattering experiments are done with unpolarized beams, and the polarization of the scattered parti... | The usual way to do this is to average over the possible incoming states, but sum over the outgoing states. In that case the 1/2 is correct as there are 2 possible incoming states. This would be correct for the scattering cross section, since you don't know what particle you started with (thus the average) and you end ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/588155",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Goldstone counting from symmetries and from the expansion in the Lagrangian Goldstone theorem states that when a continuous symmetry is broken there is a massless mode for each broken generator. To exemplify the theorem, many references consider the complex scalar theory with an $U(N)$ symmetry. The potential for the t... | If you work out the mass term using your second $H$, you will see that it is of the form
$$m^2(\chi_1+\chi_2)^2$$
Only the combination $\chi_1+\chi_2$ has a mass, and in particular the combination $\chi_1-\chi_2$ is massless.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/588321",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
What conditions are necessary to guarantee uniform circular motion? Suppose an object is subjected to a force of constant magnitude, which is always directed to the origin. And suppose we know the initial position of the object relative to the origin, and the initial velocity of the object, can we determine if the obj... | These are the equations of motion
$${\ddot{r}}\,m-m{\dot\varphi }^{2}r+F=0\tag 1$$
$$ \ddot\varphi \,r+2\,{\dot r}\,\dot\varphi=0\tag 2 $$
equation (2) is also;
$$\frac{d}{dt}\left(\,r^2\dot\varphi\right)=0$$
thus :
$$\dot{\varphi}=\frac{L}{r^2}$$
where L is a constant.
substitute $\dot\varphi$ in equation (1)
$$m\,\... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/588485",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Where is the energy involved in osmosis? Osmosis creates pressure on the side of the membrane with higher concentration. But where does the energy for this come from?
| All things naturally tend towards equilibrium, moving from high energy to low energy. Osmotic pressure is the force that helps achieve osmotic equilibrium, so it is really just a manifestation of that natural tendency. You don't really need energy to create osmotic pressure, the osmotic pressure will be present until e... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/588827",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
Can quantum measurements be the origin of thermodynamic arrow of time? We can practically consider that the microscopic interactions are symmetric with respect to time(as we can neglect weak force for many cases which is the only interaction that can violate $T$ symmetry). So I thought that the asymmetry might be due t... | Entropy is Macroscopic
As RogerJBarlow mentions in a comment, there is no need to invoke QM to explain the "arrow of time". To use the exact analogy, consider an "ideal billiard table" with the standard collection of 15 balls. Now, the macro state in which all balls are arranged in the starting triangle is very impro... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/589435",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 2
} |
How does the whole universe agree on the laws of physics? How is it possible that the every particle in the universe agrees on the laws of physics?
What enforces those laws? Might the laws change slightly across the universe in the same way the cosmic microwave background radiation (CMBR) does?
| Let's consider an example of this violation. Consider the electrostatic attraction strength (Coulomb's constant). If we compute it and get some value $k_1$ in our labs, we might conclude that it is a law of nature that $F=k q_1 q_2 /r^2$. If we look at another part of the universe we might find some $k_2 \neq k_1$. Is ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/589693",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "12",
"answer_count": 7,
"answer_id": 0
} |
Positron decay direction from muon I read that in the rest frame of a positive muon, decay positrons are preferentially emitted in the direction of the muon spin. Why is that the case?
The decay is $\mu^+\to e^+\nu_e\bar{\nu_\mu}$. Assuming that the positron is emitted at almost the speed of light, it will be a right-h... | This is the cleanest application of chirality in the weak interactions, and your instructor should have drilled it in your SM course.
The positron must be right-handed, as an antiparticle coupling to the charged weak current. The neutrino/antineutrino pair are left/right handed, respectively. All products are fast enou... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/589782",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Why does a capacitor act as a frequency filter? What is it about a capacitor which allows it to filter frequencies?
I understand the construction of a high-pass RC filter, and the mathematics behind it, but I'm struggling to find an explanation of the physics behind the phenomenon.
In my mind I can picture the broad sp... | A capacitor is an open circuit. Direct current can't flow through it because the plates of the capacitor don't contact.
However, when the current is alternating (or a signal), the electric field induced by one plate induces a current in the other plate.
That current is proportional to the capacitance and the time rate ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/590006",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "14",
"answer_count": 10,
"answer_id": 8
} |
Why is the electrostatic force felt in straight lines? When two positive charges are kept close, they get repelled in the direction of a line joining both the charges. Why is it so?
Also, why is the repulsion in a straight path?
In both the cases, the potential energy of the charge which gets repelled decreases. What... | One answer is that forces are determined by the gradient of -U, where U is the potential energy. Of course, that just raises the question of why that is so. I believe that the Principle of Least Action prescribes that particles move along the gradient, but that similarly leads to the question of why particles are con... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/590107",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "12",
"answer_count": 8,
"answer_id": 4
} |
What is the equation for gravitational time dilation? I have been studying relativity for a while now, but I am still unsure what the equation is to determine a gravitational time dilation. I am more than aware of the speed time dilation equation, but I would like the gravitational one.
| In general, the time dilation $\gamma$, is given by $\frac{d\tau}{dt}=\frac{1}{\gamma}$ where $dt=dx^0$ is the time coordinate and $d\tau^2=-\frac{1}{c^2} ds^2=-\frac{1}{c^2}g_{\mu \nu} dx^{\mu} dx^{\nu}$ is the proper time on the clock that you are calculating time dilation for. This expression is very general. It wor... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/590297",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Partial derivative of Dirac Lagrangian with respect to derivatives of fields Why is $\frac{\partial\mathcal{L}}{\partial(\partial_\nu \bar{\psi})} = 0$, for the Dirac Lagrangian $\mathcal{L} = \bar{\psi}(i \gamma^\mu \partial_\mu - m)\psi$?
This comes up in deriving the Noether current for $\psi \rightarrow e^{i\alpha}... | *
*$\psi$ and $\bar \psi$ are thought as two independent variables in the Lagrangian.
*If you write a Lagrangian as $\mathcal{L}_1 =\bar\psi(...)\psi$, you should use it to calculate the Noether current or equation of motion. If you have the other one, $\mathcal{L}_2 =\psi(...)\bar\psi$, you have to perform the deriv... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/590458",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
The possible orbits of a body about the Sun in terms of their total mechanical energy If we assume that the Sun is at rest in an inertial reference frame, the total mechanical energy ( $E$ ) of the Sun and the orbiting body is constant and equal to the sum of the kinetic energy ( $\mathcal K$ ) and the gravitational po... | The only way I know to show analytically that the trajectories are ellipses, parabolas, or hyperbolas involves solving a differential equation. In a comment, you explained that your students have only had some precalculus, so I don’t think you can demonstrate this to them, although you could certainly tell them that “i... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/590597",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Why does the $\mathbf{B}$-field of a cylindrical magnet have no $\phi$-component I have a cylindrical permanent magnet with uniform magnetization $\mathbf{M}=\mathbf{a_z}M$, length $L$ and Diameter $D$.
I'm wondering why the $\mathbf{B}$-field created by this uniform magnetization has no $\phi$-component, that is, the... | I tried explaining this before but I maybe wasn't so clear so here is my second attempt:
This is entirely do to symmetry, the magnet is cylindrical and thus viewed from above appears to be round and entirely symmetric.
Thus we have that the outcome would be exactly the same if rotated by a factor $\phi$
as the magnetis... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/590750",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
Gravitational potential energy sign Following is a small derivation just so I can explain my question. The gravitational potential energy is:
$$(*)U_g = -\frac{GMm}{r}$$
And:
$$ \Delta U =-GMm(\frac{1}{r_{final}} - \frac{1}{r_{initial}}) $$
If some mass $m$ is taken a height $h$ above the ground, we get:
$$ \Delta U =-... | Yes, potential energy decreases in the direction of the force. So potential energy decreases as you move closer to the Earth. Any texts that say potential energy increases closer to the Earth shouldn't be taken seriously. The texts could be talking about the magnitude of the potential energy, but that really isn't a us... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/590845",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Why doesn't the state of matter oscillates between solid , liquid and gaseous phase? I was reading about the London dispersion forces and it is written that it arises due to an asymmetric distribution of charges in an atom at an instant which gives rise to a temporal dipole and this temporal dipole then induces a dipol... | The dipole interactions may oscillate (at very high frequencies) but they average out over time (and billions of atoms) into a steady force. The ability of this force to hold atoms together against thermal agitation generally depends on the temperature. A change of state is associated with a significant amount of ener... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/590968",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Spin conservation in circuits with a spin filter If we have a circuit made of a battery and a resistor the number of electrons with spin up will be equal to the electrons with spin down. If we put the resistor in series with a piece of ferromagnetic material which is magnetize either up or down, let's say it is magneti... | Since you want to influence the spin of the electrons by a magnetic field, why don't we talk about the magnetic dipole of the electrons instead of their spin. At least both are connected by their alignment; under the influence of a magnetic field they get aligned with this field.
The next effect is the acting Lorentz f... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/591184",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Gravitational Field Strength of a point in between Two Planets In my textbook, under the topic of gravitation, it states that if the centres of 2 planets, each of mass $M$ and separated by a distance $r$ and you have a point halfway between the centres of the planets, the gravitational field strength at that point is... | You are correct. The two forces are in opposite directions and cancel each other.
Force is a vector quantity. When adding vectors the directions are as important as the magnitudes.
Perhaps you are confusing gravitational field strength $g=GM/r^2$ and gravitational potential $V=-GM/r$. The former is gravitational force ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/591305",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
What is the equivalent to $\Box A^\alpha =- \mu_0 J^\alpha$ using differential forms? The set of equations $$\Box A^\alpha = -\mu_0 J^\alpha$$
can be found in section 12.3.5 of Griffiths's book. From what I understand, the real-valued functions on both side of the equations are the coefficients of some $1$-forms with r... | Recall the inhomogeneous Maxwell equation in natural units:
$\newcommand{\dif}{\mathrm{d}}$
\begin{align}
\mathrm{d}*F={}*J\in\Omega^3
\end{align}
Since $**=-1$ on $\displaystyle{\Omega^1}$, the equation is equivalent to
\begin{align}
{}*\mathrm{d}*F=-J\in\Omega^1.
\end{align}
Now consider some one-form $A$ such that $... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/591410",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 2
} |
The depicted shape of subatomic particles I physics books and such, I understand why they show atoms as spheres because they have the electron cloud. But why are protons, neutrons, and electrons spheres? I guess people say that because of calculations in nuclear physics, they turn out to be a sphere, but why naturally.... | What about the colours in the pictures?
As the poet says
"Protons are Red,
Electrons are Blue,
Neutrons are Grey,
And so are You"
Colours and shapes are just artist's illustrations. Pictures don't mean anything. If they used a dot it would be too small to see it; if they used a cube it would be misleading so what ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/591548",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
Would an astronaut in this spacecraft feel weightless?
A spacecraft is placed in orbit around Saturn so that it is
Saturn-stationary (the Saturn equivalent of geostationary – the
spacecraft is always over the same point on Saturn’s surface on the
equator).
Information the question provided:
mass of saturn = $5.68\tim... | We all know a fundamental principle from physics which says, " freely falling body are weightless"
That is, their Apparent weight is zero. So what is a freely falling body.....?
Any object on or around a planet (like earth or Saturn), whose acceleration is equal to acceleration due to gravity at that point (in magnitu... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/591803",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 1
} |
Can we prove the Earth rotation with a disk mounted in its center on a frictionless axis? Can somebody prove the rotation of Earth if it places an uniform disk with a hole in its the center on an axis and orient it paralelly to Sun ecliptical disk?Just assure himself that the disk on the axis is in equilibrium and the ... | What you describe is reminiscent of a 1913 experiment by Arthur Compton. This setup is referred to as a Compton ring
A circular tube is filled with water (with suspended particles in the water to allow tracking of motion of the water).
The initial position of the tube is perpendicular to the local level surface. The wa... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/591907",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
Maxwell equations in non-transparent media There are many examples of media non-transparent for the light of visible spectrum.
What does it mean in terms of the Maxwell equations in such media? More precisely what does it mean for dielectric permittivity and magnetic permeability (which depend on the medium and on the ... | Non-transparent media is a vague term. Let me first note that when we talk about transparency, we have in mind propagation of electromagnetic waves. Non-transparent means that the waves do not propagate in this medium. Another important point: the medium does not enter directly into the Maxwell equations. However, thes... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/592035",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Confution on UV cut-off in the calculation of effective action and Beta function I am reading David Tong's gauge theory notes and meet some difficulties.
In section 2.4.2, he uses background field to calculate effective action $S_{eff}$ and Beta function. Simply like follows:
Writting gauge field $A_{\mu}$ as $A_{\mu}=... | Tong is using a cutoff regularization in this calculation, the cutoff being this $\Lambda$. Specifically this factor appears because he has just completed the loop momenta integral (integral over the momenta $p$). This integral is divergent without a regularization scheme, so of course taking $\Lambda\rightarrow\infty$... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/592216",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Might the Kaluza-Klein scalar provide a solution to the dark puzzles? Kaluza-Klein theories of a five-dimensional spacetime yield not only the equations of general relativity and electromagnetism, but also a scalar field. This scalar field, sometimes quantised as the radion or dilaton, is thought not to exist.
Given to... | Yes, Kaluza-Klein excitations might be the dark matter. See e.g. this search on arxiv.org for some papers making the connection. In particular the earliest references there (on the second page) might be most useful for you.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/592475",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 0
} |
Why is this paper stack not flat? So we have lots of paper for photocopy. They come in a bundle. What I have noticed is that There are sine curves or maybe cosine when I saw them from the side. That's Look like:
Is there any explanation for these curves?
| This is an artifact of the so-called conversion process, by which a continuous ribbon of paper hundreds or thousands of feet long and four feet wide on a huge roll is slit to width and then sheared to length and the cut sheets then stacked and wrapped into packages for shipment.
Since the initial spooling process by wh... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/592696",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 0
} |
What does intrinsic and extrinsic contribution to Hall effect mean? In the context of transportation theory (electron and thermal conductivities), what is the physical meaning of extrinsic and intrinsic contributions to the Hall effect (i.e. transverse conductivity)?
For example, in the article "Anomalous Hall effect i... | In this context, "intrinsic" means that the Hall conductivity comes from the Berry curvature. That is, it's a contribution intrinsic to the band structure. Disorder can produce "extrinsic" contributions to the anomalous Hall effect through so-called side-jump and skew-scattering mechanisms. If you're interested, you ca... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/592807",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Why are we allowed to make algebraic calculation on units Is there math proof that we can cancel out units in Physics? For example:
$\require{cancel}distance = \frac{meters}{\cancel{second}} * \cancel{second}$.
So we see that seconds cancel out and we left with meters which is correct but how is it possible if it is no... | The question seems trivial, but it isn't at all!
Some strange formal properties of algebraic calculations on units
(e.g. the elusive rad unit which appears or disappears)
should suggest that "something is wrong" instead of the
more usual W.Allen's "Whatever works".
The problem concerns the logic (syntax and semantics) ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/593069",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 4,
"answer_id": 1
} |
Why doesn't a mercury thermometer follow the rules of volume dilatation? let's consider a classic mercury thermometer.
I do not understand why it does not behave like a "normal" thermometer which exploits volume dilatation. In a normal thermometer, I'd say that the mercury length would be proportional to its temperatu... | That's because it's a maximum thermometer, which works by pushing the liquid past a restriction in the tube, preventing the liquid from returning into the reservoir upon cooling. If you look closely, you might see the separation in the liquid column between the restriction and the reservoir, which may be bigger or smal... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/593185",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "20",
"answer_count": 2,
"answer_id": 1
} |
Is the torque on a gyroscope a conventional virtual force perpendicular to rotation? So I am having some difficulty understanding gyroscopic precession. I understand that mathematically by convention torque is perpendicular to the force and so is angular momentum but surely that force is a true force acting outwards as... | I cannot add to the excellent responses earlier by others. Here are a few comments. Gyroscopic motion is hardly intuitive to anyone. My problem with basics physics discussions is they just discuss the effect of torque on the spinning gyro but do not really provide a good intuitive explanation; also, some of these di... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/593773",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 2
} |
Meson as hadron and boson In wikipedia page about hadrons the following image appears:
I can understand why the intersection between hadrons and fermions are baryons, as a way to say a baryon is a kind of hadron composed of several quark fermions.
However, what is the meaning of the intersection between hadron and bos... | Since a meson is composed of two spin 1/2 particles, its total spin must be an integer, which makes it a boson.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/593855",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 1
} |
How exactly do quantum numbers increase in relation to energy levels in more than one dimension? When you have increasing energy levels in 2 or 3 dimensions how does the values of quantum numbers $n$ increase for each dimension?
For example if you have ground state $E_1$ then you have for $(n_x,n_y,n_z)$ is $(1,1,1)$ i... | For a particle in a box (also known as a particle in an infinite potential well) in $d$ dimensions, the Hamiltonian inside the box is given by $$\hat{H}=\frac{1}{2m}\sum_{i=1}^d{p}^2_i$$where $p_i$ is the momentum operator in the $i^{\text{th}}$ direction. As you already know (I infer so from your question) that using ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/593970",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
Why does particle measurement cause quantum wavefunctions to collapse When we attempt to measure a certain property of a particle, how and why does its wave function collapse? I've tried to find answers on my own, but they've been far too complicated for me to comprehend. Would appreciate any answer with limited comple... | Not only is wave function “collapse” a misleading term, it is also not an intrinsic part of quantum mechanics. There are interpretations of quantum mechanics, such as the many-worlds interpretation, in which a wave function never collapses - it only appears to, due to our limited knowledge. If you loose one sock from a... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/594045",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 3,
"answer_id": 2
} |
Mechanical Advantage of Static Double Pulleys For a set of two double pulleys, the force acting on each should be equal to the tension in the rope times the number of ropes connected to the individual pulley if I understand correctly. In this pulley system on mcmaster, it looks as though the force acting on the upper ... | I am pretty sure you are correct.
I tried to find the mechanical advantage by using a FBD and got it to be 4:1. But just to be sure I poked around the internet a bit and found this great site. The MA is given in section 6-8.3 .
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/594275",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
Can coldness be converted to heat energy? We know that the heat can be converted into heat energy with the help of thermoelectric generators, but why can't we generate energy from coldness?
Like the temperature of the universe in 1 K, can this be used in the near future to be used as an energy resource for probes or sa... | If you want to transfer heat from a cold environment to a warm environment, you need a heat pump but then part of the provided heat will come from the work done by the heat pump, so it comes from the fuel that drives the heat pump. To get all the heat from only the cold environment, you need to use a heat pump that exp... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/594665",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "10",
"answer_count": 9,
"answer_id": 3
} |
Number and Types of States of Matter I wanted to know if there were more than 5 states of matter (man-made or natural) and so I searched it up. Other than solid, liquid, gas, plasma, and Bose-Einstein state, these were varying results from 7 to 15 different states. I want to know what the real answer is. How many state... | As long as we are lacking any fundamental physical definition to a "states of matter", we will have arbitrary amount of these states of matter. This is well discussed in this question;
What determines a state of matter?
Condensate is practically a matter, where molecules holds their relative positions to each other in ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/594779",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Is Light our limit? Suppose something existed faster than light will we be able to perceive it?
And even if we encounter it wouldn't seem to travel with speed of light?
| Superluminal objects have a big problem with the relativistic mass equation:
$$
m = {m_0 \over {\sqrt{1-{v^2\over{c^2}}}}}
$$
If you set $v=2c$ in the equation, you get
$$
m = {m_0\over{\sqrt{-3}}} \approx 0.577im_0
$$
So you get an imaginary mass.
Goodness knows what that might mean... I'll have imaginary two kilos of... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/594892",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
Why does ponytail-style hair oscillate horizontally, but not vertically when jogging? Many people with long hair tie their hair to ponytail-style:
Closely observing the movement of their hair when they are running, I have noticed that the ponytail oscillates only horizontally, that is, in "left-right direction". Never... | Very simple: The frequency for the up and down movement is twice that of the left and right swing.
Plus the up and down excitation (acceleration) is not symmetric, a good part of it consists of overtones of even higher frequency. Actually the hair and attached head are in free fall between steps.
So to get to the same ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/594964",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "41",
"answer_count": 6,
"answer_id": 5
} |
Can spacetime be curved even in absence of any source? Einstein's equation in absense of any source (i.e., $T_{ab}=0$) $$R_{ab}-\frac{1}{2}g_{ab}R=0$$ has the solution $$R_{ab}=0.$$
But I think $R_{ab}=0$ does not imply that all components of the Riemann-Christoffel curvature tensor $R^c_{dab}$ be zero (or does it?). F... | That's right. But it doesn't mean that the curvature is from nowhere. The Field equation describes the curvature (locally) at a point only from $T_{\mu \nu}$ at the same point (Since it's all built in a differential manifold and tangent spaces at each points aren't related to each other). If $T_{\mu \nu}$ is zero at a ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/595184",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 4,
"answer_id": 3
} |
Time dependence of operators In Griffiths's Introduction to Quantum Mechanics, while studying the time evolution of the expectation value of position, the author wrote:
$$\langle x\rangle=\int_{-\infty}^{+\infty}x|\Psi(x,t)|^2\,dx.$$
So
$$\frac{d\langle x\rangle}{dt}=\int x\frac{\partial}{\partial t}|\Psi(x,t)|^2\,dx.$... |
Did he just assumed that x has no time dependence? And why?
Yes. The outcome of an integral of the form
$$\int_{\mathbb{R}} f(x,t) \, \text{d}x \tag{1}$$
is a function of time $t$; that is, a function of one real variable (or, loosely speaking, the integral will evaluate to a quantity that will not depend on $x$, onl... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/595326",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 2,
"answer_id": 0
} |
Increase in temperature in a copper wire I am creating a simulation of a magnet moving relative to a copper coil generating emf in it. So far I am working with emf generated, current, resistance, resistivity, turns, coil length, and the cross-sectional area of the coil. The next step is to add the increase in temperatu... | With those quantities, you can only calculate heat generation. In steady state (when the temperature is constant), it will be equal to heat loss.
There are three mechanisms for heat loss: conduction, convection, and radiation. As long as the temperature is not too much higher than room temperature, the heat loss would ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/595466",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Feasibility of the Aharonov-Bohm effect The Aharonov-Bohm effect is often presented via a region in space where the magnetic field $\textbf B=0$, but the vector potential $\textbf A \neq 0$. Usually, this is motivated via an infinitely long solenoid, which is said to have a vanishing magnetic field outside the coil.
Ho... | Experimentally, you're never going to get field that's exactly zero. However, it would help to have 2 coaxial solenoids, one wound right on top of the other. Current flows up through one and back down through the other. The solenoid-like field is the same for both, but the wire-like field is opposite and cancels out.
| {
"language": "en",
"url": "https://physics.stackexchange.com/questions/595697",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 1,
"answer_id": 0
} |
How does radiation (heat) take away momentum? In another post, I was taught that when we are moving (running, for example), radiation (in the form of heat, both from our muscles and friction with the ground) takes away from our momentum. That makes perfect sense and I understand.
I was also taught that heat/radiation i... | Suppose that we have a lone body moving freely across space, his momentum then is conserved, it has to stay the same through time. This derives directly from the laws of dynamic. End of the story. But if the body emits radiation then some of the momentum of the body can be stolen by the photons that it emits, in fact ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/595876",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 1
} |
Why current rating of a fuse wire does not depend on its length? If legth is increased, resistance is increased and heat produced is directly proportional to the resistance. So why current rating is still independent of its length? Please give answer assuming that there is no heat loss
| A wire will melt if it exceeds a certain temperature. If resistive heating is happening in the wire, its temperature will increase until the rate of heat loss (via conduction to the air, largely) balances the rate of heat generation, or until it melts, whichever comes first. The rate of heat loss is proportional to t... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/595973",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
How do we know neutrons and electrons are distinct particles on the same scale as protons? I'm aware my question may not even make sense when considering quantum physics, but please excuse my ignorance. We are taught in school that there are basically 3 particles that make up atoms (protons, neutrons, electrons) and th... | If the electron were made up of smaller particles then we would expect to see some evidence of these smaller particles in particle collisions observed at CERN and other particle collider. We have never seen any such evidence. So as far as we know the electron is an elementary particle.
In the case of the proton and the... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/596127",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "3",
"answer_count": 3,
"answer_id": 2
} |
Isn't $\epsilon_{ij}$ an isotropic, rank-2 tensor? Definition of isotropic tensor: components are unchanged after rotation: $T_{ij}\rightarrow T_{ij}' \equiv R_{ia}R_{jb}T_{ij} = T_{ij}$
MathWorld says there is only one rank-2 isotropic tensor, $\delta_{ij}$.
But with
$$\epsilon_{ij}=\left(\begin{matrix}0&1\\-1&0\end{m... | This is only true for 2D space not in general
3D space:
$$S=\left[ \begin {array}{ccc} \cos \left( a \right) &-\sin \left( a
\right) &0\\ \sin \left( a \right) &\cos \left( a
\right) &0\\ 0&0&1\end {array} \right]
$$
and
$$\epsilon=\left[ \begin {array}{ccc} 0&-1&1\\ 1&0&-1
\\ -1&1&0\end {array} \right]
$$
$\Righta... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/596205",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "4",
"answer_count": 2,
"answer_id": 1
} |
Reason for negligible chemical potentials of different particles in early universe For the early Universe at high temperatures, the chemical potential is assumed to be zero for all types of particles is negligible. Why is this true?
| In the current universe baryon and lepton number are conserved. This means that there are two chemical potentials, $\mu_B$ and $\mu_L$. We believe that the universe has a net-baryon density, and $\mu_B\neq 0$. We don't know the net lepton number of the universe, because the net lepton number of the neutrino background ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/596339",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "2",
"answer_count": 2,
"answer_id": 0
} |
What is the work done by a force that changes with time $F(t)$? There is a force that changes with time. (F(t))
And the position vector is also given as a function time. (r(t))
Here how do we find the work done by F(t) between, lets's say t=0 and t=1?
This is my actual time-dependent force:
And this is the position ve... | The work done during a short interval of time, $[t, t+\Delta t]$ is given by usual formula
$$
\Delta W = \mathbf{F}(t)\cdot \Delta \mathbf{r}(t),
$$
where $\mathbf{F}(t)$ and $\Delta \mathbf{r}(t)$ are the force and the displacement at the beginning of the interval. The total work is then approximately a sum over all t... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/596434",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
Can two photons excite an electron consecutively? I know that a photons energy is quantized and that it can excite a bounded electron from one energy state to the other whic depends upon the energy the photon carries my question is that can two photons consequtively excite an electron from an initial state (say E1) to ... | Short answer : yes.
Why can't it? An electron can always continue to gain energy from compatible photons and move to higher and higher energy levels (till it finally leaves the atom itself!) as long as the time between the consecutive excitations is not sufficient enough for the electron to drop back to its ground stat... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/596562",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 2,
"answer_id": 0
} |
How to know what voltage to apply in hydrogen gas tub to obtain the spectrum? Generally to detect the hydrogen spectrum people uses the hydrogen gas tube as a light source. How people knows the right voltage to apply to the tube in order to obtain the hydrogen atomic spectrum.
What I mean is this, if you apply low volt... | For any gas, there is a well-known breakdown voltage at which it switches from being a good insulator to a good conductor. This "starting voltage" is the minimum voltage required to start the glow discharge. You can find breakdown voltages for different gases in a handbook of high-voltage engineering.
Then, to prevent ... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/596656",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 1,
"answer_id": 0
} |
What is angular velocity in 3-dimensional space? (Revised) If I'm not mistaken, there are analogies between the translational dynamics of a rigid body and the rotational dynamics of that body. For example, the position of a rigid body is analogous to the orientation of that body. What property of a rigid body, from a r... | Before getting to the question, let me first clarify a couple of points. Since the rotation group is three dimensional, it takes three angles to specify the orientation of a body in three dimensions with respect to some reference orientation. For example, we could specify the three Euler angles of the rotation.
Further... | {
"language": "en",
"url": "https://physics.stackexchange.com/questions/596909",
"timestamp": "2023-03-29T00:00:00",
"source": "stackexchange",
"question_score": "1",
"answer_count": 3,
"answer_id": 1
} |
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.