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80098 | Simple circuit with resistances | I have a question about a circuit that I made in class! So, we had a circuit with 2 resistors, one of $R_1 = 330 \Omega$ and one of $R_2 = 470 \Omega$. The tension applied to the circuit should be $10V$ but we applied $9.99V(V_f)$. When measuring the resistances with a multimeter the value for the $R_1$ was $328 \Omega... | Given that you measured $R_1 = 328 \Omega$, $R_2 = 470 \Omega$, and both resistors in series yield an experimental total of $R_1 + R_2 = 799 \Omega$, calculate the ideal values of the total resistance based on the measured voltages across $R_1$ and $R_2$ using Ohm’s Law and the applied voltage of $9.99V$. Compare the t... | 21,887 | cqadupstack-physics |
48529 | Semiconductors and localization of the electrons | When looking at the band diagram of a semi-conductor, direct conclusion of the invariance under discrete translations, for a filled state with an electron, one does know precisely it's momentum, so my question is: does it imply, by Heisenberg, uncertainty that this electron is spread over the whole lattice? Is it the c... | Given a semiconductor with discretely translated lattice structures, if an electron is in a filled state, what is the expected range of its position uncertainty according to Heisenberg's uncertainty principle, and how does this compare to the position uncertainty of other electrons in the same state? Calculate the posi... | 11,590 | cqadupstack-physics |
43236 | If there is significant temperature difference between indoor air and outdoor air, will that significantly increase the rate of air exchange? | There would be heat diffusion, of course, but heat diffusion occurs even without the exchange of fluid parcels between each environment. We do know that cold air tends to be denser than warm air, and that pressure differences drive the exchange of fluid parcels. But let's assume that there is no pressure difference for... | If two containers of air are at the same pressure and one contains warm air at 30°C while the other contains cold air at 10°C, calculate the average speed of heat diffusion from the warm air to the cold air, assuming the thermal conductivity of air is 0.0257 W/(m·K). How long will it take for the temperatures to equali... | 15,046 | cqadupstack-physics |
63565 | How would gravity change on a planet rotating around itself very fast? | Let's take a planet identical to Earth, but with rotation speed multiplied by ten thousand. What would happen with the gravity if it was spinning madly around itself? Would the centrifugal force make objects seem lighter than on normal Earth? Would the people on that planet be able to jump higher? | If a planet identical to Earth has a rotation speed multiplied by ten thousand, what would be the effect on the gravitational acceleration experienced by objects on its surface, and how would this change influence the maximum height a person could jump compared to Earth? | 34,751 | cqadupstack-physics |
40999 | How fast would a spaceship have to go to reach Alpha Centauri within a person's lifetime? | Given the recent news about the discovery of an "Earthlike" planet orbiting Alpha Centauri (our nearest stellar neighbour) it got me wondering just how fast would spaceship have to travel to be able to reach Alpha Centauri within a person's lifetime (say 60 years)? The reasoning is that even if we sent an unmanned prob... | What minimum speed would a spaceship need to maintain in order to reach Alpha Centauri, which is approximately 4.37 light-years away, within 60 years, assuming it can decelerate sufficiently to enter orbit around the star? | 15,155 | cqadupstack-physics |
113585 | Zitterbewegung for massless particle | Is it possible for a massless particle to undergo zitterbewegung? In massive Dirac theory the Zitterbewegung frequency comes out to be $2mc^2/\hbar$. It looks like the effect will vanish for a massless particle. But the effect is due to the interference between particle and antiparticle state which is also there for a ... | What is the theoretical frequency of Zitterbewegung for a massless particle, given that the frequency for a massive particle is calculated as \( f = \frac{2mc^2}{\hbar} \)? | 8,226 | cqadupstack-physics |
132597 | How to define tensor contraction without referring to summation? | The textbook defines a tensor to be an element in $(T^*)^k×T^l→R$. It then expresses tensors as arrays of components with respect to a certain basis, and defines tensor contraction using summation convention. My question is: Can we define tensor contraction without referring to basis, components, and summation, but jus... | Can tensor contraction be defined solely in terms of multilinear functions without the need for components or a basis, and if so, what would that definition entail? | 13,159 | cqadupstack-physics |
67476 | Dimensions of a variable celestial body? | I read (extern link to a filehoster, page 163 section 4.8) that a variable celestial object like a pulsar or quasar must be smaller than the distance the light travels in its variation period. Can someone give me a proof or a reference to a proof. | Given that a pulsar has a variation period of 0.001 seconds, calculate the maximum diameter that this pulsar can have, considering it must be smaller than the distance light travels in one variation period. Use the speed of light as 3.00 x 10^8 meters per second in your calculation. | 9,162 | cqadupstack-physics |
76232 | Remote control wireless helicopter hovering in cruising aircraft, will it move the aircraft with stability | A Mini Toy Helicopter is left for hovering inside the cabin of an Aircraft, while the aircraft is cruising at the speed of 900 Km/h. Helicopter has no contact with the surface of the aircraft. The Question is... What would happen with the toy helicopter due to the speed of the aircraft? 1: It will be stable, on its pos... | What will happen to a Mini Toy Helicopter that is hovering inside a cruising aircraft moving at 900 km/h? Will it remain stable in its position or be pushed backwards? Explain the reasoning behind your answer considering the effects of air movement and relative motion. | 10,268 | cqadupstack-physics |
66081 | Path integral representation of $\langle q_f t_f|p(t_1)|q_i t_i\rangle $ | How do I calculate path integral representation of $\langle q_f t_f|p(t_1)|q_i t_i\rangle $ where $t_i<t_1<t_f$? I am doing this by discretizing, the time intervals and adding a complete set of $|q_j t_j\rangle$ states at each point, then at the time $t_1$, one can add $p(t_1)|p^{\prime} t_1\rangle \langle p^{\prime} t... | What is the time-evolution operator for a quantum particle in a potential \( V(q) \), and how do you derive the path integral representation of the transition amplitude \( \langle q_f, t_f | p(t_1) | q_i, t_i \rangle \) using the discretization approach, incorporating momentum eigenstates at an intermediate time \( t_1... | 11,264 | cqadupstack-physics |
79145 | How to derive following thermodynamic relation? | I'd would like to derive the following $$\bigg(\frac{\partial U}{\partial V}\bigg)_T = T \bigg(\frac{\partial p}{\partial T}\bigg)_V - p$$ What I know is that the internal energy $U$ is a function of temperature and volume. Hence, a small change in $U$ can be related to changes in $T$ and $V$ by $$dU =\bigg(\frac{\part... | Can you show how to derive the equation $$\bigg(\frac{\partial U}{\partial V}\bigg)_T = T \bigg(\frac{\partial p}{\partial T}\bigg)_V - p$$ starting from the expression for the differential change in internal energy, $$dU =\bigg(\frac{\partial U}{\partial T}\bigg)_V dT + \bigg(\frac{\partial U}{\partial V}\bigg)_T dV$$... | 38,252 | cqadupstack-physics |
14434 | Does anisotropic expansion of the universe imply quintaessence? | a Recent paper establishes under solid grounds anisotropy in the expansion acceleration rate in the universe. My question is very simple: **can this anomaly be explained entirely in terms of a cosmological constant?** I suspect that by adjusting the $\alpha$ scale factor to depend not only on time but also on a unit di... | Can the observed anisotropy in the expansion acceleration rate of the universe be fully accounted for by varying the cosmological constant in relation to both time and direction? If so, what implications would this have for our understanding of the early universe's boundary conditions? | 35,300 | cqadupstack-physics |
24796 | Is Uranium renewable, or will this science fiction scenario become reality? | In my imagination, nuclear power could disapear when we use up all the uranium generating electricity, or exploding nuclear bombs. Is uranium a renewable resourse? if not, can we prove that this element could not be created by throwing neutrons and protons together? | Is uranium a renewable resource, and what is the scientific basis for the fact that it cannot be created simply by combining neutrons and protons? | 738 | cqadupstack-physics |
109985 | Is it possible to manufacture Helium? | Helium is a scarce resource, as it escapes the atmosphere over time. If we run out of Helium deposits, will it be possible to manufacture more helium through nuclear fusion or another nuclear process? If so, how much energy will be required? | What is the theoretical energy requirement for producing helium through nuclear fusion, given the fusion of deuterium and tritium, and what is the net energy yield from this reaction? | 3,787 | cqadupstack-physics |
81361 | Surely force on shell can't be balanced by field momentum? | Imagine a particle with charge $q$ at rest at the origin. It is surrounded by a concentric spherical insulating shell, also at rest, with charge $Q$ and radius $R$. At time $t=0$ I apply a constant horizontal acceleration $\mathbf{a}$ to the particle. The electromagnetic field spreads out radially in all directions fro... | Given a particle with charge \( q \) placed at the origin and surrounded by a spherical insulating shell with charge \( Q \) and radius \( R \), find the total horizontal force \( F \) exerted on the shell when the particle is subject to a constant horizontal acceleration \( \mathbf{a} \) starting from rest. Use the pr... | 6,792 | cqadupstack-physics |
135130 | How would water drain out of a sealed pipe? | While hiking through the Grand Canyon, I started wondering. Say we have a pipe for the purpose of transporting water across a canyon, with the bottom submerged in a pool of water. Like the blue line in this terribly drawn image:  Now let's seal the two ... | If a sealed U-shaped pipe filled with water has a break at the bottom of the U, how high can the water inside the pipe potentially drain before reaching a vacuum, and what would be the resultant pressure change that could lead to significant water vapor formation? | 6,169 | cqadupstack-physics |
63748 | Predicting stellar evolution and life cycle of a star | Is there a way to model/predict the evolution and life cycle of a star based on certain initial conditions? That is, whether it will become a red giant, brown dwarf, etc. I'm basically looking for equations defining the progress of different star-types and how varying initial conditions may affect that progress. | What equations can be used to predict the evolutionary path of a star, and how do variations in initial mass and composition influence whether it becomes a red giant, brown dwarf, or another type of star? | 8,895 | cqadupstack-physics |
17828 | Finding initial velocity using conservation of momentum and energy | A 14 g bullet is fired into a 120 g wooden block initially at rest on a horizontal surface. The acceleration of gravity is 9.8 m/s^2. After impact, the block slides 6.97 m before coming to rest. If the coefficient of friction between block and surface is 0.568, what was the speed of the bullet immediately before impact?... | What was the speed of the bullet immediately before it impacted the wooden block, given that a 14 g bullet is fired into a 120 g block initially at rest, causing the block to slide 6.97 m before coming to rest, with a coefficient of friction of 0.568? Please provide the answer in m/s. | 21,304 | cqadupstack-physics |
40907 | Derivation of Ohm's Law | Is it possible to derive Ohm's law (perhaps in some appropriate limit) from Maxwell's Equations? | Under what conditions or limitations can Ohm's Law be derived from Maxwell's Equations, and what are the implications of this derivation for understanding electrical conduction in materials? | 28,105 | cqadupstack-physics |
60228 | Wave equations for two intervals at Potential step | Lets say we have a potential step as in the picture:  In the region **I** there is a free particle with a wavefunction $\psi_I$ while in the region **II** the wave function will be $\psi_{II}$. Let me take now the schrödinger equation and try to derive ... | In the context of a quantum particle encountering a potential step, if the wavefunction in region I is represented as $\psi_I = C e^{i\mathcal{L} x} + D e^{-i\mathcal{L} x}$, where $\mathcal{L} = \sqrt{\frac{2mW}{\hbar^2}}$, what conditions must be met for the constants $C$ and $D$ to ensure that the wavefunction remai... | 19,074 | cqadupstack-physics |
97929 | How to calculate the total angular momentum (J) values | How can I calculate the values of $J$ (total angular momentum) for a particular term, for instance, ${}^3P$? | What is the total angular momentum $J$ for the term ${}^3P$, and how is it calculated based on the quantum numbers involved? | 33,571 | cqadupstack-physics |
102552 | Confusion about Dirac mass term | In chiral basis, $\psi=\begin{pmatrix} \psi_L\\\ \psi_R \end{pmatrix}$ and therefore, $\overline\psi=\psi^\dagger\gamma^0=\begin{pmatrix} \psi^\dagger_L & \psi^\dagger_R \end{pmatrix}\gamma^0=\begin{pmatrix} \psi^\dagger_R & \psi^\dagger_L \end{pmatrix}$. Hence, by matrix multiplication, $\overline \psi \psi=\psi^\dagg... | Given the relationship between the chiral components of a Dirac spinor, can you derive the expression for \(\overline{\psi} = \begin{pmatrix} \bar{\psi}_R & \bar{\psi}_L \end{pmatrix}\) starting from the definition \(\overline{\psi} = \psi^\dagger \gamma^0 = \begin{pmatrix} \psi^\dagger_R & \psi^\dagger_L \end{pmatrix}... | 22,593 | cqadupstack-physics |
36023 | Water Jet Cutter and Laser | I watched a video of "Glass cutting" which uses a **Water Jet Cutter**. It was said that Cutting glass simply by machines would eventually crack it... So, They're using grains of sand (by placing a sand paper beneath) to cut glass using a Water Jet. It also has enough force to cut through _steel_.  and a uniform volumetric charge density \( \rho \), and how would the result change if the charge density is not uniform and is greater near the inner surface of the shell? Could you derive an expression for... | 33,217 | cqadupstack-physics |
44300 | Isn't a single Quantum one single string? | In physics, a quantum (plural: quanta) is the minimum amount of any physical entity involved in an interaction. In Quantum Mechanics There is no difference between one Quantum to another one. According to string theory, absolutely everything in the universe—all of the particles that make up matter and forces—is compris... | If a fundamental string's resonant pattern determines the properties of different elementary particles in string theory, how many distinct patterns can theoretically exist for a string of a particular type, given that there are currently 17 known elementary particles in the Standard Model of particle physics? | 35,229 | cqadupstack-physics |
134257 | Calculus of variations applied to a rotating liquid | I thought I knew how to use calculus of variations, but then I started thinking about the problem of a rotating liquid and it confused me a great deal. It would be nice to hear your thoughts on the problem. Suppose we have a liquid in a spinning cylinder in an equilibrium (i.e. the liquid is still in the rotating frame... | In a rotating cylindrical container filled with liquid, the height of the liquid as a function of the radial coordinate is given by the equation \( h(r) = c_1 + c_2 r^2 \), where \( c_2 = \frac{\omega^2}{2g} \). Given that the volume of the liquid is constant, can you derive the relationship between the constants \( c_... | 33,843 | cqadupstack-physics |
71721 | Temperature of rod if end points are different temperature | How does the temperature vary along the length of the rod if its both ends are at different temperature. As an example, consider the problem: > 20 cm long rod has rod at one end 100 ºC and another end at 0 ºC. Find the > temperature at the center of the rod when it's in thermal steady state. | What is the temperature at the center of a 20 cm long rod in thermal steady state if one end is maintained at 100 ºC and the other end at 0 ºC? | 29,831 | cqadupstack-physics |
93203 | Material breaking underneath its breaking point (due to repeated load) | I'm trying to recall some fact that I learned in my college materials science class, where we learned concepts like stress vs. strain. I remember that materials like metal have a breaking point, and if an applied stress produces a force higher than the breaking point, the metal will break. Or something like that. Now, ... | What is the term for the phenomenon where materials, such as metals, fail due to repeated application of stress below their ultimate tensile strength, often observed in engineering failures like in airplanes or bridges? | 2,510 | cqadupstack-physics |
77172 | Example of inviscid flow with drag | This was my engineering viva question and I couldn't think of any example, for I am totally convinced that there cannot be drag in a inviscid flow. It also bothers me whether it is possible, a tricky scenario in fluid mechanics or gas dynamics. | In fluid mechanics, can you explain under what conditions drag can occur in an inviscid flow, and provide a quantitative example to illustrate this scenario? | 29,914 | cqadupstack-physics |
44020 | Download only physics and maths wikipedia pages for offline use | There are tools for downloading the entire wikipedia database (above 8 Gb without pictures), but I would like to download only physics and maths pages, to view them offline. Wikipedia pages have a tree structure in categories, so it should be possible. Please see here http://en.m.wikipedia.org/wiki/Wikipedia:Database_d... | What is the total size of the Wikipedia database for physics and mathematics topics if the full database is over 8 GB and consists of articles without pictures? | 17,714 | cqadupstack-physics |
112948 | Alternative solar panels | I was doing a bit of thinking recently, when I stumbled on an interesting idea. In a simplified sense, solar cells function by absorbing light and converting it into electrical energy. Since visible light is just electromagnetic radiation, would it be possible to build a "solar" cell that absorbs different wavelengths ... | What are the potential advantages and limitations of creating solar cells that harness different wavelengths of electromagnetic radiation, such as ultraviolet and infrared, compared to traditional visible-light solar cells, especially in the context of Earth's atmosphere? Additionally, how feasible is the idea of using... | 12,685 | cqadupstack-physics |
108326 | Why can't we detect redshift of Galaxies/Clusters moving parallel to us? | If a moving Galaxy/Cluster doesn't have radially outward motion component from us, we are unable to detect its redshift. The answer may look obvious: There's no wavelength squeezing/expanding ju-ju. But, here's my problem: As universe expands, the gravitational grip becomes weaker because it's inversely proportional to... | If a galaxy is moving parallel to us and has no radially outward motion component, why do we not observe a redshift in its light despite the effects of gravitational time dilation as the universe expands? | 26,411 | cqadupstack-physics |
98540 | Do I need mass to calculate the rms speed of diatomic Nitrogen? | Calculate the rms speed of diatomic Nitrogen ($N_2$) at an altitude of $600$ km, where the temperature is $1500$ K. I'm confused because only an altitude and a temperature is given, and I feel like I need the mass if the Nitrogen to complete the problem. $v_{rms} = \sqrt{\frac{3K_bT}{m}}$ | What is the rms speed of diatomic Nitrogen ($N_2$) at an altitude of $600$ km and a temperature of $1500$ K, given that the molar mass of $N_2$ is $28.02 \, \text{g/mol}$? | 22,639 | cqadupstack-physics |
26704 | What happens to light and mass in the center of a black hole? | I know that black holes are "black" because nothing can escape it due to the massive gravity, but I am wondering if there are any theories as to what happens to the light or mass that enters a black hole and cannot escape. | What are the current theories about the fate of light and matter that crosses the event horizon of a black hole, particularly in terms of what happens to their mass and energy? | 11,180 | cqadupstack-physics |
39226 | Lagrangian dynamics with initial conditions: motion of free particle | I am very new to Lagrangian dynamics so I am trying to get my head around the practical usage. So far on here all I could find were proofs and they did not make much sense to me, especially when time was involved in a problem. Let's take a simple example. I have a free particle, and it can be represented in Cartesian c... | How can I use the Lagrangian formulation of mechanics to determine the displacement of a free particle in Cartesian coordinates at a time $t$ given its initial position $\mathbf{r}(0)$ and velocity $\mathbf{v}(0)$? Specifically, what is the relationship between the kinetic energy and the path of the particle? | 13,358 | cqadupstack-physics |
105288 | Solve my confusion about electrons? | When a glass rod is rubbed with a silk cloth, both get charged: The silk gets positively charged and the rod gets negatively charged. My question is the following: How/why do these objects return to a more or less neutral state after a certain amount of time. The glass rod is negatively charged, that means there is a n... | Explain the process by which a negatively charged glass rod loses its excess electrons over time and returns to a neutral state. What mechanisms contribute to the dissipation of excess charge in this scenario? | 20,637 | cqadupstack-physics |
3718 | Can vectors in physics be represented by complex numbers and can they be divided? | Below is attached for reference, but the question is simply about whether vectors used in physics in a vector space can be represented by complex numbers and whether they can be divided. * * * In abstract algebra, a field is an algebraic structure with notions of addition, subtraction, multiplication, and division, sat... | Can vectors in a physics context be represented as complex numbers, and if so, can these complex number representations be divided? Provide a mathematical example to support your answer. | 28,981 | cqadupstack-physics |
30731 | What would be the requirement to learn matrix mechanics? | What would be the requirement to learn matrix mechanics? More specifically, what math do I need? Can anyone recommend me a book that covers all maths needed for matrix mechanics? | What mathematical concepts and skills are essential for understanding matrix mechanics, and can you provide a specific example of a recommended textbook that covers these topics comprehensively? | 22,438 | cqadupstack-physics |
110983 | Why was quantum mechanics regarded as a non-deterministic theory? | It seems to be a wide impression that quantum mechanics is not deterministic, e.g. the world is quantum-mechanical and not deterministic. I have a basic question about quantum mechanics itself. A quantum-mechanical object is _completely_ characterized by the state vector. The time-evolution of state vector is perfectl... | In quantum mechanics, if the state of the universe can be represented as evolving deterministically through the equation \(\hat{U}(t,t_0) \lvert \mathrm{universe} (t_0) \rangle = \lvert \mathrm{universe} (t) \rangle\) and measurements yield definite outcomes based on this state, how can one reconcile the probabilistic ... | 20,953 | cqadupstack-physics |
34652 | Is it best to look at light as a particle when trying to understand special relativity? | So my course about special relativity explains time dilation using a moving train, where one sends up (i.e. perpendicular to the direction of movement) a light pulse which gets reflected etc. (a similar example is to be found here so you guys know what I'm talking about) Let's say the source of the light pulse is a fla... | In the context of special relativity, how does the angle of the emitted light pulse from a flashlight on a moving train appear to an observer at a train station, and what is the effect on the perceived velocity of the light pulse in relation to the speed of the train? | 28,056 | cqadupstack-physics |
40822 | Regularization of infinite series: an alternative for the not-always-courteous-Zeta | Zeta-function regularization of infinite series is the most commonly used in QFT applications. However, occasionally other schemes are employed which, allegedly, suit the nature (most noticeably the underlying symmetries) of the problem at hand. An alternative to the zeta-function (used for instance at the bottom of Pa... | What conditions must be met for a regularization scheme to respect supersymmetry in quantum field theory, and could you provide an example demonstrating how the alternative regularization method described sums to zero for the series of integers? | 32,620 | cqadupstack-physics |
45341 | Representing a polarization vector for light as a 'manifold of two state' | **Explain me these projections please** **Context:** I was reading a paper (Phys. Rev. A 68, 052307) which involved **mesoscopic coherent states of light**. There, in order to calculate the uncertainty of a single **Poincaré angle** (see polarization parametrization, for both polarization elipse and Poincaré sphere) ht... | How can I calculate the projections \(\gamma\) and \(\delta\) on the \(x\) and \(y\) axes for a given Poincaré angle \((\Theta_k, \Phi_k)\) using the formulas provided, and how do these projections relate to the coherent amplitude \(\alpha\) in the context of mesoscopic coherent states of light? | 8,022 | cqadupstack-physics |
72115 | Potential energy of the dipole-dipole interaction for two parallel dipole moments | I am looking for an equation that gives me the potential energy of the interaction between two parallel dipoles. | What is the equation for the potential energy of the interaction between two parallel electric dipoles, given their dipole moments and the distance between them? | 20,313 | cqadupstack-physics |
95670 | Is the gauge fixing $\partial_\mu A^\mu + \gamma A_\mu A^\mu=0$ used in the literature and does it have a name? | In an exercise for a course on Gauge Theories, I was asked to derive the action of QED with the method by Faddeev and Popov, using the following gauge- fixing function: $$F(A) = \partial_\mu A^\mu + \gamma A_\mu A^\mu, $$ where $\gamma$ is constant. I was wondering whether this function is simply a construction for the... | What is the physical significance and application of the gauge-fixing function \( F(A) = \partial_\mu A^\mu + \gamma A_\mu A^\mu \) in Quantum Electrodynamics (QED), and how is it referenced in the literature? | 2,710 | cqadupstack-physics |
18576 | How to derive Fermi-Dirac and Bose-Einstein distribution using canonical ensemble? | My textbook says that microcanonical ensemble, canonical ensemble and grand canonical ensemble are essentially equivalent under thermodynamic limit. It also derives Fermi-Dirac and Bose-Einstein distribution from grand canonical ensemble. My question is then: How to derive Fermi-Dirac and Bose-Einstein distribution usi... | How can one derive the Fermi-Dirac and Bose-Einstein distributions using the canonical ensemble approach, given that the canonical ensemble expression $$\rho \propto e^{-\beta E}$$ appears to suggest a Boltzmann distribution? | 751 | cqadupstack-physics |
89030 | Semiconductors: why the mass action law is not valid for very low temperatures? | I thought that it was valid for very low temperatures since for it to be valid I think that it is necessary to be in the non-degeneracy condition, which requires $E_G >> k_B T$ (with $E_G$ being the energy gap), that it is satisfied at very low temperatures... But maybe at too low temperatures the non-degeneracy condit... | At what temperature can we consider the non-degeneracy condition \(E_G >> k_B T\) to be valid for a semiconductor with an energy gap \(E_G\) of 1 eV? For this question, assume \(k_B\) (Boltzmann's constant) is approximately \(8.617 \times 10^{-5} \text{ eV/K}\). | 20,511 | cqadupstack-physics |
125980 | At what temperature does air become liquid at a pressure of X bar? | ... with X = 6 in my particular case. I was trying to get a phase diagram for air, only got one for nitrogen and was slightly puzzled. Here's why: I was wondering about a particular detail in industrial air liquification. The original Linde process used 200 bar pressure and cycled the air though several cycles to conde... | What is the approximate temperature to which the regenerator in the Linde-Fränkle process is pre-cooled to achieve air liquefaction at a pressure of 6 bar, considering the phase diagram of nitrogen? | 34,216 | cqadupstack-physics |
48585 | Where and how is the entropy of a black hole stored? | Where and how is the entropy of a black hole stored? Is it around the horizon? Most of the entanglement entropy across the event horizon lies within Planck distances of it and are short lived. Is it stored near the singularity? How can you pack so much information in such a small region? Can you please help me? | What is the relationship between the entanglement entropy of a black hole and the characteristics of its event horizon, specifically regarding the spatial distribution of this entropy in relation to Planck distances? | 23,702 | cqadupstack-physics |
79 | Is quantum entanglement mediated by an interaction? | You can get two photons entangled, and send them off in different directions; this is what happens in EPR experiments. Is the entanglement then somehow affected if one puts a thick slab of EM shielding material between the entangled photons? Have such experiments been made? According to EPR experiments measurements of ... | If two entangled photons are sent in different directions and a thick slab of electromagnetic shielding is placed between them, how does this shielding affect the entanglement as measured by experiments? Are there any documented experiments that specifically address this scenario? | 7,319 | cqadupstack-physics |
100236 | Which component shows spin squeezing under twisting Hamiltonian? | Given a many body spin system, a collection of N spin-1/2 particles, under the interaction of the twisting Hamiltonian: $$H_{int} = \sum_{i,j=1}^Na_{i,j}\sigma_{z,i}\sigma_{z,j}= A J_{z}^{2}$$ assume all $a_{i,j}$ are equal and define: $$\mathbf{J} = \sum_{n=1}^{N} \mathbf{\sigma}_{n}$$ the collective spin operator, $\... | In a many-body spin system of N spin-1/2 particles under the influence of a twisting Hamiltonian, how does the variance of the spin components evolve over time, particularly along the y- and z-axes? What assumptions about the initial state, such as starting with a coherent spin state, are necessary for demonstrating sp... | 3,227 | cqadupstack-physics |
73978 | Newtonian gravity from the holographic principle? | Can one understand Newton's law of gravitation using the holographic principle (or does such reasoning just amount to dimensional analysis)? Following an argument similar to one given by Erik Verlinde, consider a mass $M$ inside a spherical volume of space of radius $R$. The holographic principle says that the mass $M$... | If we assume there are 4 degrees of freedom per string, what is the relationship between the mass \( M \), radius \( R \), and the Unruh temperature \( T \) for an object falling through the surface of a spherical volume as derived from the holographic principle, and how does this relate to the gravitational accelerati... | 29,041 | cqadupstack-physics |
93356 | AC Electromagnets | Could someone help explain the uses of AC electromagnets. Wherever I look it says that DC electromagnets create stronger magnetic fields. I understand why AC electromagnets could be used in transformers but why use them in motors for example? Power stations also use electromagnets in the generator to create the magneti... | What are the advantages of using AC electromagnets in electric motors compared to DC electromagnets, and what type of current is typically used in household appliances like food processors and blenders? | 14,514 | cqadupstack-physics |
122439 | Is the field generated by an electromagnet always proportional to its current? | Imagine that I use a long wire to create an electromagnet. Let's also assume that the current flowing along the wire is constant, and that the wire is winded on the vacuumm. Is the magnetic field generated by this electromagnet (current flowing over an arbitrary path on a finite volume) proportional to the current? | If a long wire is wound into a solenoid configuration in a vacuum and a constant current of 3 A flows through it, what is the strength of the magnetic field B (in teslas) at the center of the solenoid, assuming it has 500 turns and a length of 1 meter? Use the formula \( B = \mu_0 \frac{N I}{L} \), where \( \mu_0 \) is... | 24,052 | cqadupstack-physics |
26674 | Photographs of galaxies many light years far from the Earth | Using ground-based telescopes or the Hubble Space Telescope, astronomers take photographs of galaxies which are many light years from the Earth. Does it mean those photographs are as old as the galaxies are far from the Earth? As I read that the Universe is growing very radidly, then its position and shape should have ... | When astronomers take photographs of galaxies that are billions of light years away using telescopes, how many years ago did the light they captured actually leave those galaxies, given that the speed of light is approximately 300,000 kilometers per second? | 5,587 | cqadupstack-physics |
39519 | Looking for a complete review of the BEC-BCS crossover | I'm looking for comprehensive review of the BEC-BCS crossover, both from a theoretical point of view, and from a experimental one. Even something at textbook level, but exhaustive, would be OK, but I can't find this topic on the Condensed Matter Theory books I use (Altland, Annett). In particular I know that some quant... | What are the key differences in the critical temperature and pairing mechanisms between BEC (Bose-Einstein Condensate) and BCS (Bardeen-Cooper-Schrieffer) superconductivity, and how have these differences been experimentally verified? | 12,891 | cqadupstack-physics |
76599 | Mysteries of the water meter | Recently, I got an exceptionally high bill for water consumption. I went to check my water meter, and saw that it rotates in a pace of about 200 cc per minute, even though all the faucets in my home are closed. So, I concluded that there is probably a hidden leakage somewhere in my home. But then I did the following ex... | What could explain the sudden increase in the water meter's rotation to 400 cc per second after reopening the main faucet, given that it was previously rotating consistently at 200 cc per minute with all faucets closed? | 19,239 | cqadupstack-physics |
41115 | Why is water not used as a dielectric in the condenser? | The dielectric constant of water is very high. Then why is it not used as a dielectric in the condenser? | Given that the dielectric constant of water is approximately 80, calculate the maximum electric field that can be applied across a parallel plate capacitor filled with water, assuming the breakdown strength of water is 3 MV/m. What factors may limit the practical use of water as a dielectric in capacitors despite its h... | 2,696 | cqadupstack-physics |
119679 | EXAFS (Extended X-Ray Absorption Fine Structure) question? | EXAFS (Extended X-Ray Absorption Fine Structure), core electron is excited to the conduction band. The oscillations in the absorption coefficient persist for 100s of eV after the edge. Taking fourier transform of the exafs function gives the R space peak positions that are related to the bond lengths. http://cars9.uchi... | What are the expected R space peak positions for pure metals in EXAFS analysis, and how do they compare to experimentally measured values? Are there specific databases where these bond lengths can be found? | 1,921 | cqadupstack-physics |
39382 | Large gauge transformations | I would like to understand what is the importance of large gauge transformations. I read that these gauge transformation cannot be deformed to the identity, but why should we care about that? | What is the mathematical significance of large gauge transformations in gauge theory, and how do their properties differentiate them from small gauge transformations in physical applications? | 3,867 | cqadupstack-physics |
70993 | How energy curves spacetime? | We know through General Relativity (GR) that matter curves spacetime (ST) like a "ball curves a trampoline" but then how energy curves spacetime? Is it just like matter curvature of ST? | How does the curvature of spacetime caused by energy compare quantitatively to the curvature caused by matter, and what are the specific mathematical expressions used to describe these effects in General Relativity? | 4,336 | cqadupstack-physics |
121362 | Does the Bohr van Leeuwen Theorem also apply to ferromagnetism? | I know that the Bohr-van Leeuwen theorem shows that there could be not consistent pure classical explanation of dia- and paramagnetism. Does the same theorem also rule out a consistent classical theory of ferromagnetism? Do you have any realiable references for this? | Does the Bohr-van Leeuwen theorem imply that ferromagnetism cannot be explained by a classical theory, and if so, what are the fundamental reasons behind this conclusion? | 6,211 | cqadupstack-physics |
78625 | Prove a dielectric with infinite dielectric constant behaves as a conductor for static fields | I read the following problem: Prove that a dielectric medium for which $\varepsilon \to \infty$ behaves as a perfect conductor in the presence of static electric fields. So, the easy part is that the normal component of an electric field is cancelled when entering the medium, as in a conductor. We also know that the ta... | How can we mathematically demonstrate that an ideal dielectric with infinite permittivity has an equipotential surface when subjected to a static electric field, leading to the conclusion that the total electric field is normal to the surface? | 36,434 | cqadupstack-physics |
60956 | How to calculate beam spread of a non-point light source via an aspheric lens | I need to determine the angle, or rate of divergence of light from a single aspheric lens when I place a non-point light source (e.g. LED array) at a given distance from the lens which is less than the focal length of the lens. This seems to fall outside of the normal emphasis on image size and location in all the begi... | What is the formula to calculate the angle of divergence of light from an aspheric lens when a non-point light source, such as an LED array, is placed at a distance less than the lens's focal length, given the source's beam angle and radius? | 9,350 | cqadupstack-physics |
116701 | How does the viscosity (besides density) of a fluid affects sinking | If water, air of whatever fluid had a different viscosity, but the same density, would things fall/sink differently? | How does the viscosity of a fluid affect the terminal velocity of an object falling through it, if the density of the fluid remains constant? | 3,960 | cqadupstack-physics |
16131 | What is the definition of a 2-cocycle in Quantum Mechanics | I'm having this lecture on QM and we are giving an introduction on Lie Groups. So... this week we have been talking about central extensions of LG (such as Galilean) and related to this popped up the 2-cocycles. All I know is that they should relate somehow the phases of its projective representation and by that should... | What is the significance of 2-cocycles in the context of central extensions of Lie groups, particularly regarding their role in defining the phases of projective representations, and can you provide a concrete example of a 2-cocycle for the Galilean group? | 17,534 | cqadupstack-physics |
107035 | Saddle point and transition state of a molecule | During a transition of a molecule from one state to another, it pass through a transition state. This transition state, mathematically speaking, is a saddle point. That means, the second derivative along all the coordinates, except one, is greater than zero. I have two questions: 1) Is it possible for a molecule to hav... | In a diatomic molecule undergoing a reaction, if the potential energy surface shows no saddle point, what can be inferred about the existence of a transition state, and how does this relate to the energy landscape of the reaction? | 17,532 | cqadupstack-physics |
26044 | Population I and II stars | I have been thinking about the formation of the galaxy. I can easily understand that old, low-metallicity stars are in the halo, but I'm missing something when it comes to the disk. If slowly-rotating gas settled into the disk, formed stars, then did the disk at one time consist of Population II stars which have since ... | What are the main differences in the formation and evolution processes of Population I and Population II stars in the disk and halo of a galaxy, and how do these processes affect their presence in each region? | 17,640 | cqadupstack-physics |
59227 | US time zones and Daylight saving time, energy efficient? | As a foreigner, United States has a very complex time system for me. `Central Time Zone`, `North American Eastern Time Zone`, `Mountain Time Zone`, `Alaska Time Zone`, `Pacific Time Zone`, `Samoa Time Zone`, `Atlantic Time Zone`, `Hawaii–Aleutian Time Zone`. And also plus `DST` (`Daylight saving time`). I heard people ... | What is the average amount of energy saved per household during Daylight Saving Time as reported in scientific studies, and how does this compare to energy consumption patterns outside of this time period? | 27,060 | cqadupstack-physics |
56102 | Weakly Guiding Approximation | I was reading a chapter on Fiber Optics and I encountered `Weakly Guiding Approximation`. I am reading John M. Senior and it says `Optical fibers used in communication purposes follow weakly guiding approximation where the relative refractive index (delta) is much less than 1.`I tried searching different sources but wi... | What is the formula to calculate the relative refractive index (delta) in a weakly guiding optical fiber, and how does a relative refractive index significantly less than 1 affect the fiber's performance in communication? | 222 | cqadupstack-physics |
95762 | How do you extract cosmological constants like $k$ or $H_0$ from the fluctuations in the CMBR (WMAP)? | I am currently reading a book about Astrophysics and also tried to find some information about it on the web, but was not able to figure it out. That is why I ask you guys now. Any help is greatly appreciated :) I understand that the CMBR of approximately $3\,\textrm{K}$ has fluctuations of $\frac{\Delta T}{T}\approx 1... | How can the Hubble constant ($H_0$) and the curvature constant ($k$) of the universe be determined from the Cosmic Microwave Background Radiation (CMBR) data, particularly in the context of WMAP observations, and what implications does assuming a flat universe ($k=0$) have on these measurements? | 19,501 | cqadupstack-physics |
18358 | Does a car use friction to move? | When a car's engine injects fuel into the cylinder chambers, the reaction creates a force that generates rotational momentum to the shaft and over the transmission, it translates that power to the wheels, right? But, something's bothering me, how does the car actually move, is it dependent on the force of friction? Whe... | If a car's wheels experience a force exerted on the road due to the engine's drive force, what is the minimum value of the force of friction required to prevent the wheels from spinning in place, assuming a known mass of the car and a specific coefficient of static friction for the tires on the road? | 34,888 | cqadupstack-physics |
63152 | Computational Fluid Dynamics methods | I have read some articles about the finite difference method on a cartesian orthogonal grid. I understand how it works when Dirichlet boundary conditions are used, or when Neumann boundary conditions are used on a simple boundary (for example the rectangular boundary of the simulation). What I don't understand is how t... | How can the finite difference method be applied to simulate potential flow around a circle in a 2D Cartesian grid using Neumann boundary conditions, considering the circle is approximated by a series of squares? What specific steps should I follow to accurately represent the circular boundary and implement the Neumann ... | 24,744 | cqadupstack-physics |
15169 | If the earth has gravity, why don't we all collapse to the center? | I'm sorry if the answer is obvious for you guys, but why don't we all (including buildings, road, people, the ground) collapse to the center of the earth because of gravity? Is it because we have velocity, just like the earth not falling to the sun (or electrons not falling to the protons)? But that analogy doesn't sou... | Why don't objects on the surface of the Earth, including buildings and people, fall into the center of the Earth due to gravity? Provide a quantitative explanation involving gravitational force and the concept of centripetal acceleration. | 14,767 | cqadupstack-physics |
107945 | light entering a black hole's singularity | I already understand that light cannot escape a black hole after passing the event horizon, so please do not explain that to me. What I would like to know is this: a well known fact about light (a photon specifically) is that it travels at the speed of light, and at no other speed, which means that it has no rest mass,... | As a photon spirals closer to the singularity of a black hole, how does the time experienced by the photon compare to the time experienced by an outside observer, and what happens to the photon's speed as it approaches the event horizon? | 28,336 | cqadupstack-physics |
19597 | Is there a known optical design for a beam compressor? | With my little knowledge of optics I have come across some 'known' designs such as the Double Gauss for example, is there a 'beam compressor'. My requirements are to reduce an incoming parallel wavefront (source at infinity) to either an outgoing parallel beam (ie afocal), by a factor of around 100 within 10cm or comin... | What optical design or configuration can efficiently compress an incoming parallel wavefront to achieve an outgoing parallel beam that is reduced by a factor of 100, or focuses at an f-number of around 4 or 5, within a distance of 10 cm? | 10,559 | cqadupstack-physics |
71894 | Dielectric with polar molecules | Suppose a dielectric slab contains polar molecules (which are not further polarisable). When placed in an electric field, (for simplicity, an uniform field), align themselves according to the field. * Do they perfectly align so that all molecules have no net torque on them, or it is only a general arrangement which i... | How does the ratio of the electric field strength (E) to the thermal energy per molecule (given by \( \frac{1}{2}k_b T \)) affect the degree of alignment of polar molecules in a dielectric material when placed in an electric field? Provide a quantitative relationship or formula that describes this interaction. | 37,259 | cqadupstack-physics |
58128 | Transfer functions of active filters | I've been looking for some straightforward method or trick to obtain the transfer functions of active filters (like the Sallen-Key filter, the butterworth or Cauer topology etc...) since KCL or KVL requires a lot of algebraic manipulations. I've heard that SFG (signal flow graphs) could be very helpful, but with my min... | What are the transfer functions for a Sallen-Key low-pass filter when the following component values are used: R1 = 10 kΩ, R2 = 10 kΩ, C1 = 100 nF, and C2 = 100 nF? | 5,134 | cqadupstack-physics |
41735 | Is flying really easier on smaller scales? | In the book Playing with Planets, the author makes the following argument, pertinent to flying robots of the future: > As it is, an important law of physics says that smaller organisms fly much > more easily than larger ones. This can be seen clearly in living organisms: > small animals have a lot less trouble getting ... | How does the Reynolds number influence the flight efficiency of small flying robots compared to larger ones, and what implications does this have for their design and energy consumption? | 21,488 | cqadupstack-physics |
101388 | "Spooky action at a distance" or particle correlation at the time of their creation? | In Bell test experiments, two particles that are a singlet are measured and are found to be correlated. The correlation leads us to believe that they are somehow connected non- locally: the measurement of one particle results in affecting the other particle instantaneously. My question is this: have we ruled out the po... | In Bell test experiments with two correlated singlet particles, what is the probability that the observed correlations are due to pre-existing properties of the particles at the moment of their creation, rather than due to instantaneous state transmission between them? Provide a quantitative analysis based on the princ... | 24,543 | cqadupstack-physics |
90743 | At what frequency does the medium of air change from acoustic to light? | I'm calculating the max doppler frequency of a fading channel in an in-room environment and looking at different carrier frequencies. Calculated as follows: F = vf/c Where F -> max doppler shift v -> Velocity of object f -> carrier freq c -> speed of waves in medium At lower frequencies (ultrasound), I use the sp... | At what frequency does the transition occur between using the speed of sound and the speed of light for calculating the maximum Doppler frequency in a fading channel? | 35,063 | cqadupstack-physics |
4156 | Are Classical Field Theory and Quantum Mechanics of a single particle (nonrelativistic or "classical") limits of Quantum Field Theory? | Recently I talked about QFT with another physicist and mentioned that the Quantum Field Theory of a fermion is a quantisation of its one-particle quantum mechanical theory. He denied this and responded that he rather sees the single particle QM as the non-relativistic limit of a QFT. He elaborated that the energies enc... | In quantum field theory (QFT), how does the mass of a particle influence the relationship between its relativistic and non-relativistic limits, particularly in the case of fermions and massless particles like photons? | 21,794 | cqadupstack-physics |
59440 | Calculate Capacitance in Series AC Circuits? | I'm supposed to calculate the capacitance of an unknown capacitor in series, but I'm not sure exactly which equation to use. I know the voltage across the resistor (Vr), voltage across the capacitor (Vc), the total voltage (V), the resistance value of the resistor (R), the frequency (f), and since I was using an oscill... | Using the given voltage across the resistor (Vr), voltage across the capacitor (Vc), total voltage (V), resistance (R), frequency (f), and the time difference (Δt) measured with an oscilloscope, how can I calculate the capacitance (C) of the unknown capacitor in a series circuit? What specific equation should I use, an... | 5,218 | cqadupstack-physics |
61047 | quantization of angular momentum | What is the most direct way of observation of quantization of angular momentum? | What experimental evidence demonstrates the quantization of angular momentum in electrons orbiting an atom? | 14,668 | cqadupstack-physics |
28677 | RC circuit theory and voltage in the capacitor vs Ohm's Law | Consider a simple series RC circuit at steady state (capacitor is full). I've been told that once the capacitor is full we can literally "cut" the circuit because no current can flow. That argument makes sense, but because the capacitor is full, doesn't that also mean it has a potential difference across it? In other w... | In a simple RC circuit at steady state where the capacitor is fully charged, why does the current drop to zero despite the capacitor maintaining a potential difference across its plates? Additionally, can you explain the significance of the equation \( I = I_0 e^{-t/\tau} \) in the context of capacitor discharge in suc... | 14,314 | cqadupstack-physics |
132819 | Trying to make a realistic simulation of 'breaks' (Pool) | I'm working on a 2D pool simulation project right now, and I'm trying to create good looking physics that are also performant. After collisions are detected, I update the velocities of the balls. So far, I've assumed collisions are elastic, which gives pretty good results. The formulas for the final velocities of both ... | In a 2D pool simulation, if two balls of equal mass collide elastically and the coefficient of restitution is adjusted to a value slightly less than 1 (for example, 0.9), what would be the formulas for the final velocities of both balls after the collision, assuming the initial velocities are known? How would the resul... | 12,412 | cqadupstack-physics |
81001 | How can you calculate air resistances at different speeds? | I've read that at 50mph air resistance to an average car is the equivalent of driving through water and at 80mph it's the equivalent of driving through oil. I can't find any references online to back up these figures. Is there a relatively simple way to explain the calculation to verify these figures, or are they incor... | What is the approximate drag force experienced by an average car at 50 mph and 80 mph, and how does it compare to the buoyant resistance experienced when moving through water and oil, assuming the car's frontal area and drag coefficient remain constant? | 24,169 | cqadupstack-physics |
67160 | The role of state space composition in quantum computation | In a paper by Richard Josza and Noah Linden they argue that the way state spaces of composite systems are formed is a key aspect in the benefits of quantum computers. In (classical) phase space, two systems are composed by the Cartesian product, whereas in (quantum) Hilbert space, they're composed by the tensor product... | If we limit a quantum computing model to using only a single qudit with a very high number of levels, would this constraint cause all quantum complexity classes to collapse to their classical equivalents? Justify your answer with an explanation of the implications of using a single qudit in terms of state manipulation ... | 10,751 | cqadupstack-physics |
133278 | Solenoid pull force & Velocity calculation | So I am building a circular accelerator (like a slightly oversimplified model version of CERN) as a physics project, and I'm at a dead end. I believe I need to know how to work out differential equations to answer this, but I'd like to know if there's any other way to get the answer. Okay. I am calculating the velocity... | Given a solenoid with parameters \(N\), \(I\), \(\mu_0\), \(A\), and the average gap \(g_{avg}\) between the solenoid and a projectile, how can you accurately calculate the force \(F\) acting on the projectile? Additionally, if the mass of the projectile is \(m\), and the projectile starts with an initial velocity \(v_... | 18,682 | cqadupstack-physics |
45417 | Searching for a collaborator for a physics simulation of multi-party elections | I have completed a series of physics simulations on Matlab to find the equilibrium positions of parties in 2-D or 3-D voting space and compared them to the optimal positions that would provide the maximum average voter satisfaction. The physics aspects are in the use of forces that attract parties to voters. Would anyo... | What is the mathematical formula used to determine the optimal equilibrium position of parties in a multi-dimensional voting space to maximize voter satisfaction, considering the forces acting between parties and voters? | 30,412 | cqadupstack-physics |
110399 | How Long does it take for a roller coaster cart to reach point $x_1$? | Assume that we have a particle with weight m and initial speed v0, that follows a roller coaster path y(x).  Assuming no energy loss to friction or air resistance, the total energy in the system is $$E0 = m g y(x0) + 0.5 m vo^2$$ then the speed at each point $x_... | Given a particle of mass \( m \) that starts with an initial speed \( v_0 \) at a height \( y(x_0) \), and follows a frictionless roller coaster path \( y(x) \), how can we express the speed \( v(x_f) \) of the particle at a specific point \( x_f \) in terms of \( m \), \( g \), \( y(x_0) \), and \( v_0 \)? Additionall... | 20,306 | cqadupstack-physics |
134706 | Difference between Veneziano amplitude and Virasoro shapiro amplitude | I have been study about Veneziano amplitude and Virasoro Shapiro amplitude. I want to summarize this two amplitude in the following way, please check that i am understand them properly. Veneziano amplitude : they are open string amplitude for disk. Usually we called four-open string tachyon on disk as Veneziano amplitu... | What are the key differences and similarities between the Veneziano amplitude and the Virasoro-Shapiro amplitude in terms of their mathematical formulations and physical interpretations? | 8,269 | cqadupstack-physics |
71677 | quantization with constraints | let be a Hamiltonian system $ H= H(x,p) $ for this system there is a conserved quantity namely $ C=xp $ so the total system is invariant under rotation if we 'quantizy' this function $ Cf(x)=\lambda _{n}f(x) $ the result is known and $ f(x)= Ax^{{1/2}+i\lambda _{n}} $ for some constant 'A' then how is this function $ f... | How does the presence of a conserved quantity related to the symmetry of a Hamiltonian system affect the quantization of the Hamiltonian, particularly in relation to the energy eigenvalues \( E_n \) and the wave function \( \Psi(x,t) \)? | 14,972 | cqadupstack-physics |
11957 | Why do prescription glasses that darken in sunlight fail to darken when the light travels through a car windshield? | I was going to buy this add on, as I almost exclusively use my sunglasses for driving. I'm just stacking them over my normal ones now... but it's quite annoying that I almost paid the extra $$$ for this feature. Found out at the last second, luckily. | If the extra feature for the sunglasses costs $50 and the standard sunglasses cost $120, what percentage of the total cost would the feature represent if the person had decided to buy it? | 35,200 | cqadupstack-physics |
126102 | Difference between single mode and multi mode optical fibres? | What is the difference between single mode and multi mode optical fibres? First off, I guess that by _modes_ we mean the spatial modes of the electric (or magnetic?) field right? Now: what makes a fibre able to support more than a single mode? I mean, what aspect of its structure corresponds to which mode(s) can be tra... | What is the maximum number of modes that a multimode optical fiber can support if its core diameter is 50 micrometers and the wavelength of the light source used is 850 nanometers? | 34,198 | cqadupstack-physics |
40989 | Friction due to air drag at high speeds | I am trying to set up this problem, but I am not sure how to go about doing so. (From University Physics, Young & Freedman): > You throw a baseball straight up. The drag force is proportional to $v^2$. > In terms of $g$, what is the y-component of the ball’s acceleration when its > speed is half its terminal speed and ... | What is the y-component of the ball’s acceleration when it is moving upwards at half its terminal speed, and how does it compare to the y-component of the ball's acceleration when it is moving downwards at the same speed? For this scenario, express your answers in terms of the acceleration due to gravity, \( g \). | 35,579 | cqadupstack-physics |
34713 | If the nucleation bubble radius is greater than the deSitter radius, does that make the de Sitter space stable? | In our de Sitter phase, the cosmological constant is tiny. $10^{-123}M_P^4$. Suppose there is another phase with a lower vacuum energy. Is de Sitter phase still stable? The tunneling bubble radius has to exceed the de Sitter radius. Suppose a metastable decay to such a bubble happened. Take that final state, and evolve... | In a de Sitter phase where the cosmological constant is \(10^{-123}M_P^4\), if a new phase with a lower vacuum energy can exist, what is the minimum matter density required in the de Sitter phase to ensure that a tunneling bubble radius remains smaller than the de Sitter radius, thereby confirming the stability of the ... | 19,462 | cqadupstack-physics |
130096 | Magnetic flux of a loop due to another loop | The scenario is the following, I am given 2 loops with the same radius, r, a distance of d, and same current of I. In the left loop the current goes counter clockwise, in the right loop the current is clockwise. The two loops centers lie on the same axis which are perpendicular to the plane of the loops. I am asked to ... | Given two circular loops of radius \( r \) carrying the same current \( I \) but in opposite directions, separated by a distance \( d \), calculate the total magnetic flux \( \Phi_L \) through the left loop due to the magnetic field generated by the right loop. Assume that \( d \) is much greater than \( r \) so that t... | 10,481 | cqadupstack-physics |
62561 | Laughlin state unique ground state? | In the FQHE, one typically encounters the statement that the $\nu = 1/3$ Laughlin state is a **unique** exact ground state of a model Hamiltonian where the Haldane pseudopotentials $V_1 \neq 0$ and $V_m = 0$ for $m = 3, 5, \cdots$.(See link to a book with such a statement) Qn 1) Is this the same as a hard-core interact... | What is the relationship between the uniqueness of the $\nu = 1/3$ Laughlin state as an exact ground state of a Hamiltonian with Haldane pseudopotentials $V_1 \neq 0$ and $V_m = 0$ for odd $m$, and a hard-core interaction model described by a potential $v(r) = \partial_r^2 \delta(r)$? Specifically, can you clarify how ... | 21,941 | cqadupstack-physics |
11304 | What happen when a gas is being heated far beyond its boiling point? | let's say we pour some water to the Sun. Or boil water on 2000 degrees Celsius on Earth. | What would happen to a volume of water poured onto the Sun, assuming it could reach the surface, in terms of its phase changes and thermal energy interactions? Additionally, at what temperature in degrees Celsius would water completely vaporize under standard atmospheric pressure on Earth? | 6,648 | cqadupstack-physics |
12147 | Does my model aircraft propeller beat the sound barrier? | I fly model aircraft. Recently I changed from a "1300kv" motor to a "1500kv" motor. The difference is in speed; the 1300kv can go about 16,400rpm full- throttle and with a fully charged battery and the 1500kv can go nearly 19,000rpm. (This is no load speed, but the prop adds very little load when the aircraft is not fl... | If a model aircraft with a 7-inch diameter propeller rotates at 19,000 RPM, what is the speed of the air being displaced by the propeller at its tip, and does this speed exceed the speed of sound in air (approximately 343 m/s at room temperature)? | 28,308 | cqadupstack-physics |
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