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72226 | How does spin appear in QFT? | In QFT, as I read, it appears naturally. It is connected with Poincare algebra, doesn't it? __ As explanation of the main part of the question. Operator of relativistic orbital angular momentum 4-tensor and 4-impulse operator creates Poincare algebra. It follows that eigenvalues of vector of angular momentum operator ... | What are the possible eigenvalues of the angular momentum operator in quantum field theory when considering only orbital angular momentum, and how do they differ from the eigenvalues obtained when including spin? | 23,799 | cqadupstack-physics |
126584 | Ground state Phase Diagram of Bose-Hubbard Model | The Hamiltonian of Bose-Hubbard model reads as $$H=-J\sum\limits_{<i,j>}b_i^{\dagger}b_j+h.c.+\frac{U}{2}\sum\limits_{i}n_i(n_i-1)-\mu\sum\limits_in_i~~~~~~~~~(1)$$ For this we plot phase diagram in ( $J/U$, $\mu/U$ ) space. Same way if I want to plot phase diagram of Hamiltonian which looks like $$H=-J\sum\limits_{<i,... | How can I numerically obtain the phase diagram of the second Hamiltonian $$H=-J\sum\limits_{<i,j>}b_i^{\dagger}b_j+h.c.+\frac{U}{2}\sum\limits_{i}n_i(n_i-1)$$ in the ($J/U$, $\mu/U$) parameter space using Exact Diagonalization, and what specific features should I look for in the phase diagram? | 13,652 | cqadupstack-physics |
22717 | Does this Zeilinger group result provide experimental proof of backward-in-time causation? | Does this recent Zeilinger group delayed choice entanglement experiment imply backward-in-time influences? http://arxiv.org/abs/1203.4834 From the abstract: "This can also be viewed as “quantum steering into the past ”." | In the context of the delayed choice entanglement experiment conducted by Zeilinger's group, what is the maximum number of photons that can be generated simultaneously in a single entangled pair setup, considering the constraints of current technology? | 28,090 | cqadupstack-physics |
35238 | How thick does steel have to be to be able to withstand 300 bar (sphere) | How thick does the material in a sphere have to be to withstand the (inner)pressure of 300 bar if the material is steel? (With an inner-radius of 2cm) Atmosphere pressure = same as 0 meter above sea level Is there some "golden rule" like sqrt(bar)cm thickness times stress-constant? | What is the minimum thickness of a steel sphere with an inner radius of 2 cm that can withstand an internal pressure of 300 bar, considering the yield strength of the material? | 4,197 | cqadupstack-physics |
9170 | Bell Tests using position measurement | I don't know about all the details of Bell tests using methods like parametric down conversion, but at least in some versions of the EPR paradox you get two photons moving apart in opposite directions. I wonder if you can look for detection coincidences by using photographic plates instead of coincidence counters? The ... | In a Bell test experiment using parametric down-conversion, if two photons are emitted and sent to opposite sides with photographic plates as detectors, how would the presence of crossed polarizers affect the number of detected coincidences, and has this specific experimental setup been performed or proposed in previou... | 2,715 | cqadupstack-physics |
20502 | Angular velocity $\omega$ by $v$ | We have two girls, with mass ($M$). They become close to each other in speed of $V$. The distance between them is $3L$.  I was asked to calculate the Angular velocity ($\omega$) of the two girls. So I set the rotation axis in the middle (where the distance between the t... | Given two girls with a mass \( M \) each, moving towards each other with a speed \( V \), and initially located at a distance of \( 3L \), calculate the correct angular velocity \( \omega \) when they rotate around a common center of mass. Provide your reasoning and identify any mistakes in the method previously used t... | 26,736 | cqadupstack-physics |
18328 | What is a single word that describes the idea of the second time derivative of energy? | I think about position, its time derivative speed, and its second time derivative, acceleration. I would like to identify a single word that can be used as a handle for the second time derivative of energy (i.e., the time derivative of power). If there is a widely used term, I'd prefer to use it. If not, I'd like to ge... | What is the term commonly used to refer to the time derivative of power in the context of physics, representing the second time derivative of energy? | 17,409 | cqadupstack-physics |
123230 | Local symmetry and General Relativity | First I want to consider an example of 1D motion. Lagrange equation: $$ \frac{d}{dt} \frac{\partial L}{\partial \dot x} - \frac{\partial L}{\partial x} = 0 $$ If we transform $ L \rightarrow L+a $ with $a$ a is constant, the equation of motion remains unchanged. This is global symmetry. To obtain local symmetry we want... | In the context of transforming the Lagrangian \( L \) under local symmetries, if you consider the term \( a(x) \) as a function of position in one-dimensional space, how does the presence of the local transformation \( L \rightarrow L + a(x) \) affect the equations of motion, and how can this be mathematically expresse... | 17,736 | cqadupstack-physics |
45283 | How to find the distance of the source of sound in this problem? | On a cloudy day, the sound of thunder was heard 4.5 s after the flash of light was seen. How far was the cloud? Given that speed of sound = 340 m/s **This is what I've tried:** speed of light(c) = 10^6 * speed of sound( _v_ ) therefore, speed of light=340*10^6 m/s If _x_ is the distance of the cloud, then ... | If the sound of thunder was heard 4.5 seconds after the flash of light was seen, and the speed of sound is 340 m/s, what is the distance from the observer to the cloud in meters? | 30,945 | cqadupstack-physics |
44039 | Getting a given wavelength radio signal given an antenna with real-world constraints | Supposing you are given a transmitting antenna of whatever type of metal is most commonly used these days, and supposing that you are applying an AC current with the intent of transmitting a 1 m wavelength radio signal, about how far is one electron likely to make it in one direction along the antenna conductor in one ... | What is the average displacement of an individual electron in a metallic conductor during one half cycle of an alternating current that transmits a 1 m wavelength radio signal, and how does this relate to the production of the electromagnetic wave despite the seemingly small movement of each charge carrier? | 5,281 | cqadupstack-physics |
111977 | VEV of tensor fields | Is it possible to have a VEV (vacuum expectation value) for tensor field? I am mainly concerned about second rank tensors. It seems it can have a VEV which will be proportional to the metric tensor (in flat space-time). Does this make any sense at all? If it does, then what are it's implications? | What are the implications of a second rank tensor field having a vacuum expectation value (VEV) proportional to the metric tensor in flat spacetime, particularly in terms of physical observables or symmetry properties? | 33,315 | cqadupstack-physics |
113397 | Reason for establishing a magnetic hysteresis curve in Zeeman effect experiment | I am new to StackExchange, and so apologize in advance for any issues with the formatting of the question/appropriateness of the question to this forum. My lab partner and I were conducting a standard undergraduate laboratory experiment investigating the Zeeman splitting of the red spectral line from a cadmium lamp. Th... | What is the significance of establishing a magnetic hysteresis loop in the context of measuring the Zeeman splitting of spectral lines, and why is it important to degauss the electromagnet before conducting these measurements? | 1,708 | cqadupstack-physics |
73016 | WolframAlpha wont reckognize a second derivative inside an integral | I know that _WolframAlpha_ questions are off topic but as I cannot find a Q&A site for WA I decided to ask here. It should be a piece of cake for you guys as I think it is a fairly simple question. I have been trying to calculate my derivative in WolframAlpha by inputing this: A=0.921/10^(9), a=1*10^... | What is the numerical value of the integral
\[
\int\limits_{-\tfrac{\pi}{2}a}^{\tfrac{\pi}{2}a} A\cos^2\left(\tfrac{x}{a}\right)\left[-\tfrac{\hbar^2}{2m}\tfrac{d^2}{dx^2}\left(A\cos^2\left(\tfrac{x}{a}\right)\right)\right] \,dx
\]
given that \( A = \frac{0.921}{10^9} \), \( a = 1 \times 10^{-9} \), \( \hbar = 1.05... | 30,458 | cqadupstack-physics |
126241 | Electrostatics with Yukawa mass | I seem to have forgotten how to solve Laplace's equation when there is a Yukawa mass $\mu$. I want to find the Yukawa potential due to a homogeneously charged sphere of radius $R$ and charge density $\rho$. **My attempt** I need to solve $(\nabla^2-\mu^2)\phi = -\rho$ inside and outside the sphere. Since there is spher... | What boundary condition can be applied at the surface of the sphere \( r = R \) to determine the constant \( C \) in the Yukawa potential solution? | 56 | cqadupstack-physics |
24155 | Infinitely charged wire and Differential form of Gauss' Law | I have tried calculating the potential of a charged wire the direct way. If lambda is the charge density of the wire, then I get $$\phi(r) = \frac{\lambda}{4 \pi \epsilon_0 r} \int_{-\infty}^\infty \frac{1}{(1+z^2/r^2)^{1/2}} dz.$$ But this comes to $+\infty$ unless I am doing the calculation wrong. Why doesn't this wo... | How do you calculate the electric potential \( \phi(r) \) at a distance \( r \) from an infinitely long, uniformly charged wire with linear charge density \( \lambda \), and what does Gauss's law say about the electric field generated by such a wire? Additionally, how does this approach differ when considering an infin... | 7,546 | cqadupstack-physics |
24367 | If randomness doesn't exist, how come the universe isn't a perfect sphere with predictable distribution of matter? | I'm presuming that the scientific community pretty much agrees that randomness doesn't exits, and that everything has a cause. Please correct me if I'm wrong, I've heard of quantum mechanics, but as far as I know, it only says that it is impossible to know the electron's position and speed in the same time, because of ... | What is the role of randomness in the formation of the universe, particularly in the context of quantum mechanics and the Big Bang, and how does it comply with or contradict the laws of physics? | 13,949 | cqadupstack-physics |
92479 | Pick marginal circles in phase plot of a non-linear dynamic system | **Context** : I'm studying non-linear dynamics with _Mathematica_. **Part of the problem** : Given the following system: $\ddot{x} = x - x^3 - 0.2 \dot{x} + g(\sin(t) + \cos(2t))$, find two values of $g$ that correspond to two marginal circles. I'm not sure whether I translate it correctly. A marginal circle is a close... | Given the differential equation \(\ddot{x} = x - x^3 - 0.2 \dot{x} + g(\sin(t) + \cos(2t))\), determine two values of the parameter \(g\) that produce marginal circles in the corresponding phase space. What are the specific values of \(g\) and how do you verify that the corresponding closed phase curves are indeed marg... | 17,208 | cqadupstack-physics |
38909 | Why is developable surface developable (ie. can be flattened onto a plane without distortion)? | The course _Differential Geometry_ told me that developable surfaces, of which the Gaussian curvature is $0$, can be flattened onto a plane without distortion. Some says this is because a developable surface can have the same metric as a plane. But I still think **metric** here is a little abstract, since I can't figur... | Can you explain how a developable surface, with Gaussian curvature of zero, relates to the physical properties of paper folding, and why it can be flattened onto a plane without distortion? What specific characteristics of a developable surface allow it to maintain its metric similar to that of a plane? | 24,329 | cqadupstack-physics |
122887 | Non-additivity of energy (thermodynamics) | In page 15, Chapter 1 (Laws of Thermodynamics) of the book "An Introduction to the Study of Stellar Structure" by Nobel laureate S. Chandrasekhar, it is mentioned (in context of total energy of two subsystems brought in contact): > In general when two bodies are brought in contact, the energy is not > additive; it is e... | In the context of thermodynamics, how does the non-additive nature of energy for two bodies in contact relate to their common surface area, and how can this be quantified for large volumes? | 34,467 | cqadupstack-physics |
65568 | How long would it take for a container in vacuum to leak half of its air? | Let's say I know the size of the container, size of the hole the air leaks through, pressure the air is under and temperature of the air if that helps anything. Is it possible to calculate this only from these variables? What is the formula for how fast air leaks out of a hole? | Given a container with a volume of 2 m³, a hole with a diameter of 0.01 m, the air pressure inside the container is 200 kPa, and the temperature is 300 K, how can you calculate the rate of air leakage through the hole? What is the specific formula you would use for this calculation? | 6,999 | cqadupstack-physics |
8020 | Does the foam on top of boiling maple sap affect the rate of evaporation? | This is a serious question from someone engaged in evaporating large quantities of water to turn sap into syrup at this time of year. Probably some background will help. When sap boils vigorously it creates quite a bit of foam, which will overflow the evaporator (incidentally filling the building with a pleasing maple ... | How does the presence of foam affect the rate of evaporation of water when boiling sap to make syrup, and what are the underlying physical principles that explain this effect? | 37,938 | cqadupstack-physics |
63313 | Physical explanation for why total internal reflection occurs | I have been trying to understand total internal reflection (and have read several posts on this site already). Mathematically, I feel that I understand how the evanescent wave decays exponentially as it crosses a boundary surface and why there is no transmission. However, I have no intuition as to why it happens. Is th... | What is the critical angle for total internal reflection when light travels from water (n = 1.33) to air (n = 1.00), and how does the intensity of the evanescent wave change with distance from the boundary surface? | 4,059 | cqadupstack-physics |
95504 | Bending a flat sheet | I am interested in the following problem: starting from a flat sheet, once can bend it into a (sector) of a cylinder isometrically. If further (orthogonal to the first plane) curvature is induced, the sheet will necessarily be stretched. The question is, how much stretch is locally caused by the increase in curvature? ... | Given a flat sheet that is initially bent into a sector of a cylinder, how much stretch occurs in the material of the sheet when orthogonal curvature is induced? Please derive the local stretch using principles from differential geometry, and provide the relevant mathematical relationships to calculate the amount of st... | 21,943 | cqadupstack-physics |
23543 | Are quantum mechanics and quantum physics the same field? | What is the difference between _quantum mechanics_ and _quantum physics_? | What are the key mathematical principles that differentiate quantum mechanics from quantum physics? | 4,932 | cqadupstack-physics |
70938 | Photoelectric effect - calculating a current in the photocell in which only $5\%$ of photons manage to cause the effect | I have been trying to solve a problem about photocell and have obtained the wrong result. Can anyone tell me where did I go wrong? So it is easier I will write down all my calculations. > We have a photocell and we shine a light with of $\lambda=550nm$ on a > cathode with a surface $4mm^2$. On the surface of the cathod... | What is the correct current flowing through the photocell if only 5% of the incoming photons with a wavelength of 550 nm cause the photoelectric effect, given a power density of \( j = 1 \times 10^3 \, \text{W/m}^2 \) and a cathode surface area of \( 4 \, \text{mm}^2 \)? Use the appropriate voltage related to the stopp... | 23,079 | cqadupstack-physics |
101010 | How we disproved aether wind? | We know that the universe is not vacuum. The average temperature of the universe is 3° above absolute zero. So some "aether" really exist, but that is not some gas with very low density, but stardust. (I know that aether was only concept for spreading of light in medium, but aether wind should exist.) So why we don't c... | What is the average energy density of the universe at a temperature of 3 Kelvin above absolute zero, and how does this relate to the concept of stardust as a medium for light propagation? | 9,720 | cqadupstack-physics |
95473 | Time dilation and relativity | We've just started with relativity and I got a question regarding an exercise we got. A spaceship passes by earth on its way to planet X, at the moment it passes by Anna is born on the spaceship. Can the spaceship travel fast enough so that it reaches planet X before Anna's first birthday(spaceships clock), and if so, ... | A spaceship is traveling toward a planet located 100 light-years from Earth. If a baby is born on the spaceship at the moment it passes Earth, what minimum speed (as a fraction of the speed of light, c) must the spaceship travel to reach the planet before the baby turns one year old according to the spaceship's clock? ... | 22,868 | cqadupstack-physics |
15667 | The topology of a "closed" universe - is it really closed? | The spatial part of the positive curvature FRW metric has the form \begin{equation} ds^2=\frac{dr^2}{1-(r/R)^2}+r^2d\Omega^2 \end{equation} or \begin{equation} ds^2=R^2(d\chi^2+\sin{\chi}^2d\Omega^2) \end{equation} This is described as "closed", as it has the metric of a three-sphere, but I want to know what this actua... | What is the geometric significance of the parameter \(\chi\) in the closed Friedmann-Robertson-Walker (FRW) metric, and how does the interval of \(\chi\) relate to the topology of the universe described by this metric? Specifically, how do we reconcile the notion of a "closed" universe with the apparent restriction of ... | 13,381 | cqadupstack-physics |
113791 | Simple question regarding the Green's function for the diffusion equation | The differential operator for diffusion in three dimensions is given by $\partial_t - k \nabla^2$ where $k$ is a constant. The Green's function is (according to Wikipedia) $$\theta(t)\left( \frac{1}{4\pi k t} \right)^{3/2} e^{-r^2/4kt}$$ where $\theta$ is the Heaviside step function and $r = |\mathbf{r}|$. Hence, we sh... | Can you show how applying the differential operator \((\partial_t - k \nabla^2)\) to the Green's function \(\theta(t)\left( \frac{1}{4\pi k t} \right)^{3/2} e^{-r^2/4kt}\) results in the delta functions \(\delta(t)\delta^3(\mathbf{r})\)? Specifically, what calculation leads to this identity? | 16,896 | cqadupstack-physics |
31254 | Can the lightning be captured and used as power source? | I would like to update my knowledge in this area, that is really out-of-dated and stopped somewhere like ten years ago. I asked the very same question on my physics lecture at my studies and got the answer, that although some tests and experiments were made (by French scientists?), there is no material, either natural ... | What recent advancements have been made in materials or technologies that can withstand direct lightning strikes and potentially capture and store energy from lightning for future use? | 30,817 | cqadupstack-physics |
96459 | Physical plausibility of the Inverted Pyramid puzzle | The inverted pyramid puzzle has the following premises: > A giant inverted steel pyramid is perfectly balanced on its point. Any > movement of the pyramid will cause it to topple over. Underneath the pyramid > is a $100 bill. How do you remove the bill without disturbing the pyramid? The answer to puzzle is here. Physi... | If a giant solid steel inverted pyramid, similar in size to those in Egypt, is balanced on its point, what is the minimum amount of horizontal force a human would need to apply to initiate movement of such a pyramid, assuming the coefficient of static friction between steel and the ground is 0.5? Consider the pyramid t... | 31,917 | cqadupstack-physics |
24704 | Is there any significance to 1.21 GW? | In connection with a related question on Science Fiction & Fantasy Stack Exchange page: does this number 1.21 GW make any sense? What is 1.21 GWatts? With what can you compare it? Can the lightning really produce this amount of power? Are there any idea of why this number was used in a physical sense? | What is the total energy output in joules of a 1.21 gigawatt (GW) power source operating continuously for 1 hour, and how does this compare to the average energy released by a lightning strike? | 9,017 | cqadupstack-physics |
70431 | Is there an equivalent of a scalar potential for torques? | For a given scalar potential $V$, it is known that the corresponding force field $\mathbf{F}$ can be computed from $$ \mathbf{F} = -\nabla V $$ Suppose a rigid body is placed inside this potential. The torque on the body $\mathbf{T}$ exerted by the scalar field will be $$ \begin{align} \mathbf{T} &= \int_M \left( \math... | Given a scalar potential \( V \) and the force field defined by \( \mathbf{F} = -\nabla V \), can you find an expression for the torque \( \mathbf{T} \) on a rigid body in terms of the potential and the moment of inertia tensor \( I \)? Specifically, is there a scalar potential \( P \) related to \( V \) such that the ... | 23,769 | cqadupstack-physics |
104550 | How did the scientific community receive Einstein's theories when he published them? | By now, we have had multiple indications through observations and experiments that Einstein's theories on general and special relativity are correct. We recently had our second observation of gravitational waves (predicted by Einstein), we haven't found anything yet which goes faster than light (like Einstein said was ... | What was the general reaction of the scientific community in the early 20th century to Einstein's theories of general and special relativity, especially considering the significant departure from Newtonian physics? Was there a notable majority of acceptance, skepticism, or a combination of both? | 11,455 | cqadupstack-physics |
113209 | Speed of light as a universal speed limit | It follows from special relativity that nothing can travel faster than light. Einstein believed this would have to hold so generally that he assumed the Einstein-Podolsky-Rosen paradox to indicate a contradiction in quantum physics. Nowadays we know we have to be a bit more specific, and maybe it would be safe to say t... | If a hypothetical particle could travel faster than the speed of light, what would be the implications for causality in a relativistic framework, specifically regarding the potential to influence past events? Quantitatively, can you demonstrate how a faster-than-light signal could produce a causal paradox using spaceti... | 18,720 | cqadupstack-physics |
123167 | Partial derivatives in Lagrangian formalism | Suppose I have a function $f = xy$. A partial derivative of $f$ with respect to $x$ implies holding $y$ constant: $$ \frac{\partial f}{\partial x} = y $$ Does this mean that in order to evaluate this derivative, $y$ cannot depend on $x$? For example, if $y = x$ then $$ \frac{\partial f}{\partial x} = \frac{\partial (x^... | If you have a function \( f = xy \) and calculate the partial derivative \( \frac{\partial f}{\partial x} \) while holding \( y \) constant, how does this differentiation reconcile with the fact that \( y \) could be a function of \( x \), such as \( y = g(x) \)? Specifically, can you provide an example where \( y = g(... | 3,562 | cqadupstack-physics |
24250 | An electron is subjected to an electromagnetic field using the canonical equations solve | So I was given the following vector field: $\vec{A}(t)=\\{A_{0x}cos(\omega t + \phi_x), A_{0y}cos(\omega t + \phi_y), A_{0z}cos(\omega t + \phi_z)\\}$ Where the amplitudes $A_{0i}$ and phase shifts \phi_i are constants. An electron is moving through this field with the constant initial velocity: $\vec{v}_0=\\{v_{0x},v_... | What is the condition on the phase shift \(\phi_z\) such that an electron moving through the given vector field \(\vec{A}(t)\) at a constant initial velocity \(\vec{v}_0 = \{v_{0x}, v_{0y}, 0\}\) will never return to the metal surface at \(z < 0\) after being emitted? Additionally, calculate the average drift velocity ... | 10,560 | cqadupstack-physics |
48703 | Radioactivity and quantum superpositions | In the Schrödinger's cat experiment 'there is a tiny bit of radioactive substance, so small that perhaps in the course of the hour, one of the atoms decays'. The rest of the experiment magnifies this into a macroscopic superposition, but I want to know more about the claim that the radioactive decay produces a superpos... | What experimental methods have been used to test the concept of quantum superposition resulting from radioactive decay, particularly in situations where a single atom is in a superposition of decayed and undecayed states, and how does the large number of atoms in typical samples affect the observation of such superposi... | 6,887 | cqadupstack-physics |
11303 | what cools bottle of water faster: ice or snow | Imagine you have a pile of snow and a pile of ice shards. You put a soda bottle which has a room temperature into both piles. Which bottle is going to cool down faster? | If a soda bottle at room temperature is placed in a pile of snow and another bottle is placed in a pile of ice shards, which bottle will reach a temperature of 0 degrees Celsius faster, and what factors influence the cooling rate in each scenario? | 11,613 | cqadupstack-physics |
22281 | Relationship between nuclear spin and nuclear magnetic moment? | We know that nuclear magnetic moment can be expressed in terms of the expected value for nuclear spin as: $$\langle\mu\rangle =[g_lj+(g_s-g_l)\langle s_z\rangle]\frac{\mu_N}{\hbar}$$ (Cf. Krane), where $\vec{j}$ is the _total_ angular momentum, $\vec{l}+\vec{s}$. How does the expected $\langle s_z\rangle$ value relate ... | How can you express the expected value of the $z$-component of nuclear spin, $\langle s_z \rangle$, in terms of the total angular momentum, $\langle j \rangle$, and its projection along the $z$-axis for a given nuclear state? What is the relationship between $\langle s_z \rangle$ and the total angular momentum represen... | 5,520 | cqadupstack-physics |
83436 | Is there a fundamental difference between the statistical methods of science, comparing medicine to physics? | Is there a fundamental difference between the statistical methods of science, comparing medicine/biology with small sample sizes(n < 10^2 or 10^3) to the statistics applied in Quantum Mechanics (h: order 10^34) or statistical mechanics (N: order 10^23) | Compare the challenges and statistical methods used in experimental biology with small sample sizes (n < 100) to those used in quantum mechanics, particularly focusing on the implications of the extremely large numbers involved in statistical mechanics (N ≈ 10^23). What are some specific examples of how these differenc... | 17,566 | cqadupstack-physics |
6754 | Coriolis effect on Tsunami | The Japanese tsunami, moving at about 700 km/h, affected areas as distant as Chile's coast, 20 hours after the earthquake. How does the Coriolis force affect tsunami? Also, I saw an image of a boat caught within a large whirlpool. Is the whirlpool's rotation due to Coriolis force? | How long would it take for a tsunami traveling at 700 km/h to reach a location 10,000 km away, and what role does the Coriolis force play in altering its path? | 21,165 | cqadupstack-physics |
112991 | Integral equations contradict The Uncertainty Principle? | I was reading about Integral equations, and I found this excerpt in Portuguese Wikipedia: > "integral equations serve to determine the position in all instances of an > object, if known, its instantaneous velocity at all times" But reading about the Uncertainty Principle, I found this excerpt: > For instance, in 1927, ... | Can you explain how the concept of integral equations, which allows the determination of an object's position and instantaneous velocity, aligns with Heisenberg's Uncertainty Principle, which states that precise knowledge of position limits the precision of momentum? | 9,155 | cqadupstack-physics |
33323 | End position of movement factoring in deceleration | Ok I am hoping to apply this answer to a piece of software, but it uses physics to work out the result so I require some help in that department. I will attempt to explain this the best I can. I need to work out the continual position of a scrolling list. If you were to flick the list it would continue to scroll (witho... | What is the final position of a scrolling list after 2400 ms, given that the initial velocity is calculated based on a user flick (determined by the distance and time of the user's touch), and that the scrolling decelerates by a factor of 0.95 every 325 ms? Please provide the calculation for the position at 100 ms inte... | 6,765 | cqadupstack-physics |
127611 | Counting Problems in Physics | What are some _classic_ counting problems in physics? I'm trying to think of interesting examples to give in a math class on the matter, and I feel as if physics should have some ones to offer. | Can you provide an example of a classic counting problem in physics that can be quantitatively solved, along with the solution? | 12,881 | cqadupstack-physics |
2361 | How long will the Universe's hydrogen reserves last for? | I recently became really interested in learning about physics and cosmology, but I still know very little. Hopefully someone with more knowledge will be able to shed some light on my questions. Here are my presumptions (please correct me if I'm mistaken): * $t_{0}$: Big Bang. * The Universe expands (and thus cools)... | What is the theoretical maximum number of generations of stars that the Universe can support, considering the finite amount of Hydrogen and the processes of stellar nucleosynthesis, and how many years might this correspond to? | 11,710 | cqadupstack-physics |
52697 | What does net mechanical efficiency mean? | I often see the term "net mechanical efficiency" used in literature, but I am not quite sure what it means, and what the difference is between it and "normal" efficiency. Take this sentence for example: `... increased the effectiveness, while reducing net mechanical efficiency.` What does exactly does this mean? | What is the formula for calculating net mechanical efficiency in a machine, and how does it differ quantitatively from the overall efficiency of the same machine? | 9,634 | cqadupstack-physics |
86428 | Calculate required voltage in mixed circuits | > **Q:** Calculate the voltage that V1 has to provide > > **Given:** The following circuit. The voltage through LAMP1 is 5.0V. A (U,I) > chart (not shown). LAMP1 and LAMP2 are identical, non-ohmic lightbulbs.  My attempt at this problem: LAMP1 and LAMP2 are two identical li... | What voltage must V1 provide in a circuit with two identical, non-ohmic lightbulbs, where the voltage across LAMP1 is measured to be 5.0 V and the current through LAMP1 corresponds to 0.63 A? | 11,130 | cqadupstack-physics |
103061 | Speed of Sound/Push in Supersonic Flight | I've learned from things like the Veritasium Slink Drop and the old "break the speed of light by pushing on the end of a very long pole" thought experiment that objects have a "speed of push" which is commonly referred to as the speed of sound. My understanding of this being that information about movement can't propag... | What phenomenon occurs when a supersonic jet flies through the air, and how does this affect the pressure waves produced by the jet? | 37,342 | cqadupstack-physics |
128032 | About the definition of expectation value in quantum mechanics | In quantum mechanics, the expectation value of a observable $A$ is defined as $$\int\Psi^*\hat A\Psi$$ But in probability theory the expectation is a property of a random variable, with respect to a probability distribution:$$E(X):=\int X\;d\mu$$ I can't see how probability theory can be adapted to quantum mechanics. O... | How does the concept of expectation values in quantum mechanics relate to the framework of probability theory, particularly regarding linear operators and measurable functions? Can you explain the mathematical transition from the expectation of a random variable in probability to the expectation value of an observable ... | 10,823 | cqadupstack-physics |
78362 | Frame of Reference Question | I'm having trouble understanding this frame of reference question. > You are traveling in a car going at a constant speed of 100 km/hr down a > long, straight highway. You pass another car going in the same direction > which is traveling at a constant speed of 80 km/hr. As measured from your > car’s reference frame thi... | If you are traveling in a car at a constant speed of 100 km/hr and pass another car traveling at 80 km/hr in the same direction, what is the acceleration of your car as observed from the other car's reference frame, and what is the acceleration of the other car as observed from your reference frame? | 15,731 | cqadupstack-physics |
11311 | Using the Scalar Electrostatic Potential to Calculate Transition Probabilities | **transition probabilites** of atomic systems prone to some time-varying electromagnetic field are very often calculated using **perturbation theory** leading to expressions including the vector potential $\mathbf{A}$. This approach seems to be very complicated and I am wondering: > ### Is using the electrostatic poten... | Is it possible to calculate the transition amplitude \( A_{n\rightarrow m} \) for electric excitations in an atomic system subjected to a time-varying electromagnetic field using only the electrostatic potential \( U(\mathbf{x}) \cdot T(t) \), and if so, under what conditions would this approximation be valid? | 10,246 | cqadupstack-physics |
25128 | How can a spiral galaxy exist? | A spiral arm orbiting a central mass should be dispersed quite quickly as the outer elements would move more slowly than the inner ones. The Milky Way, is about 59 Galactic Years old, which, one would have thought, would be enough rotations to disperse a spiral structure entirely. Is there, then, something keeping the ... | What physical mechanisms or forces could explain the preservation of spiral arms in galaxies like the Milky Way, despite the differential rotation speeds of their stellar components? | 4,478 | cqadupstack-physics |
94845 | Velocity distribution in Plummer's models and others mass distributions | The Plummer's sphere is an model for the mass density in a globular cluster of stars. For an $N$-body simulation I have initialized the position of $N$ masses with a Monte-Carlo technique but cannot find a way of initializing the velocity initial conditions. Is there a simple function that given a position in a Plummer... | How can I derive the initial velocity for a mass located at a given position in a Plummer sphere, taking into account the gravitational interactions typical of a globular cluster, and what would be the implications for velocities not lying in the $x$-$y$ plane? | 19,213 | cqadupstack-physics |
56970 | XOR gate; transistor level design | * * * What would a transistor level design of an XOR gate look like? * * * | Design a transistor-level schematic for a 2-input XOR gate and calculate the total number of transistors used in your design. | 35,491 | cqadupstack-physics |
60472 | Pauli paramagnetism for electrons with external magnetic field | Apparently it is to be shown that for electrons under an external magnetic field, in the limit as $B\to 0 $ $$ \chi = \frac{dM}{dB} \approx \frac{n\,\mu^{*^2}}{k\,T}\,\frac{f_{1/2}(z)}{f_{3/2}(z)} $$ So this is the Pauli paramagnetism problem and I understand the effect and the physics, but cannot seem to get the reque... | How do you calculate the limit of the magnetic susceptibility \(\chi\) as \(B \to 0\) for a system of electrons in a magnetic field using the ratio of the Fermi-Dirac functions \(f_{1/2}(z)\) and \(f_{3/2}(z)\)? Specifically, what is the expression for this ratio in the context of Pauli paramagnetism? | 3,391 | cqadupstack-physics |
100124 | Time Dilation Effects from simply being on a spinning planet orbiting a star in a rotating galaxy in an expanding universe. | I am a layman, so take this with a grain of salt. I saw a TV show the other day which showed a Russian Cosmonaut who had spent more time in space than any other human. The relativistic effects of the low gravity and extreme speeds at which he had spent a decent part of his life had pushed him a small, but surprisingly ... | What is the cumulative relativistic effect on the aging of a person living on Earth, as compared to a hypothetical observer at rest in space, considering Earth's orbital velocity around the Sun, the Sun's orbit around the Milky Way, and the Milky Way's motion within the universe? How much time would a person on Earth e... | 26,660 | cqadupstack-physics |
47158 | Classical vs. Quantum use of the spin 4-vector | I have a few basic questions about the Pauli-Lubanski spin 4-vector S. 1. I've used it in quantum mechanical calculations as an operator, that is to say each of the components of S is a matrix operator that operates on an eigenvector or eigenspinor. But my question is about the utility of S in a classical sense, that... | What is the form of the Pauli-Lubanski spin 4-vector \( S \) for an electron that is spin-up along the z-axis in its rest frame, and how do the spatial components of \( S \) transform under a Lorentz boost to an arbitrary frame? Specifically, do the boosted spatial components still correspond to the physical spin angul... | 17,692 | cqadupstack-physics |
24857 | What are the pros and cons of a german equatorial mount vs. a fork mount? | Not much more to add. Why pick one over another? | What criteria should be considered when choosing between two different biological models, and how can their effectiveness be quantitatively assessed? | 1,312 | cqadupstack-physics |
68787 | A question about speed | > A object with mass 0.5 kg slides in straight line for 200 m, where the > friction act on it is 0.4 times the normal reaction acting on it. Find its > initial speed. I let $u$ be the speed. $u^2=2as=2*0.4mg*200=2*0.4*0.5*9.81*200,u=28.01ms^{-1}$. But the answer should be $40ms^{-1}$, can someone tell me what's wrong w... | An object with a mass of 0.5 kg slides over a distance of 200 m while experiencing friction that is 0.4 times the normal force acting on it. Can you calculate the initial speed of the object if it comes to a stop after traveling that distance? Please show your work and explain any corrections made to reach the correct ... | 23,350 | cqadupstack-physics |
91722 | Emmy Noether's theorem in simpler terms | I'd like to understand Noether's theorem and its contents as to what it implies in a bit simpler terms. I am familiar with mathematics unto Calculus 1,2,3 and some linear algebra and group theory. I am familiar with that for each symmetry there is a conservation law. 1. Now is there a one-one correspondence between t... | If Noether's theorem states that every continuous symmetry corresponds to a conservation law, can you provide an example illustrating this relationship, specifically detailing a continuous symmetry and the associated conservation law it implies? | 5,428 | cqadupstack-physics |
10088 | Why does gravity need to be quantised? | The electroweak and strong forces seem to be completely different types of forces to gravity. The latter is geometric while the former are not (as far as I'm aware!). So why should they all be described in the same way? - Why are gravitons needed? Alternatively, I suppose my question is why a theory of everything has t... | What is the theoretical mass of the graviton, assuming it is a massless particle, and how does this assumption impact the unification of gravity with the other fundamental forces? | 6,233 | cqadupstack-physics |
27433 | Looking for description of Helstrom's measurement | I hope someone can help me find the page or chapter where Helstrom discusses his famous measurement for distinguishing between two mixtures in the textbook _Quantum Detection and Estimation Theory_. Thanks in advance. | In the textbook _Quantum Detection and Estimation Theory_, what page or chapter number does Helstrom provide his renowned measurement method for distinguishing between two mixtures? | 20,608 | cqadupstack-physics |
106348 | Question regarding temperature as a property of a system | This is probably silly question but I got stuck while reading “Lectures on Theoretical Physics-Thermodynamics and Statistical Mechanics” by Sommerfeld. In the first chapter it says : > Temperature is a property or parameter of state. It is independent of the > previous history of the body and is defined solely by its i... | In a thermodynamic system, if water is heated from 10 degrees Celsius to 20 degrees Celsius, what role does the concept of temperature as an independent state property play in this process, specifically in relation to the first law of thermodynamics? | 23,399 | cqadupstack-physics |
18070 | What is escape velocity? In reality, how can something no longer be under the gravitational influence of something else? | Isn't G a continuous function and although you leave the immediate vicinity of the earth with an escape velocity won't it always exert a force, however small it may be. Won't that force eventually pull the object back to the earth (assuming the absence of other objects) | If an object is launched from the Earth's surface at escape velocity, what is the minimum gravitational force exerted on the object by the Earth as it moves away, assuming no other forces are acting on it? Provide the gravitational force at a distance of 10,000 kilometers from the Earth's center. | 34,221 | cqadupstack-physics |
10611 | Energy Levels of 3D Isotropic Harmonic Oscillator (Nuclear Shell Model) | One simple way of detailing the very basic structure of the nuclear shell model involves placing the nucleons in a 3D isotropic oscillator. It's easy to show that the energy eigenvalues are $E = \hbar\omega\left(n+\frac{3}{2}\right)$ with a degeneracy of $D(n) = \frac{1}{2}(n+1)(n+2)$, where $n = n_1 + n_2 + n_3 = a^\d... | What is the significance of the quantum numbers \( n_r \) and \( \ell \) in the context of nuclear energy levels, and how does the relationship \( n = 2n_r + \ell \) help account for the observed magic numbers in nuclei? | 4,915 | cqadupstack-physics |
53520 | How is energy produced in Alpha emission (radioactivity)? |  In the above Alpha decay reaction, we get thorium by the alpha decay of uranium with an alpha particle. But we also get energy of amount Q by this process. And according to my course books, this Q energy comes from E = mc2 i.e. some of the mass is conv... | In the alpha decay of uranium to form thorium and an alpha particle, how much energy is released if the mass of the original uranium nucleus is 238.02891 u, the mass of the thorium nucleus is 234.02863 u, and the mass of the alpha particle is 4.00260 u? Use Einstein's equation, E = mc², to calculate the energy released... | 2,427 | cqadupstack-physics |
112887 | What will happen if the solar system leaves the milky way galaxy? | Is the milky way galaxy meaningful to us? Will any bad thing happen if the solar system just leaves the galaxy? | What would be the consequences for the solar system if it were to leave the Milky Way galaxy, considering the gravitational forces and potential interactions with other cosmic structures? | 22,031 | cqadupstack-physics |
122617 | Distribution of temperature in a plume of a jet | The exaust gases of a plume of a missile have a distribution in temperature and in density vs. distance from the nozzle. Using a CFD software it is quite simple to get such distribution. Is there some analytical model useful to get this information | What analytical model can be used to predict the temperature and density distribution of exhaust gases in a missile plume as a function of distance from the nozzle? | 32,538 | cqadupstack-physics |
78561 | Angular momentum of quantum system | **Problem:** A physical system is in the common eigenstate of $\hat{L^2}$ and $\hat{L_z}$. Calculate the following quantities: $\langle L_x\rangle,\langle L_y\rangle,\langle L_z\rangle,\langle L_x L_y + L_y L_x\rangle$. **Solution:** I am not sure on where to start from. Since the physical system is in the common eigen... | A quantum system is in a common eigenstate of the operators \(\hat{L}^2\) and \(\hat{L}_z\). If the eigenvalues associated with these operators are \(L^2 = \hbar^2 \ell (\ell + 1)\) and \(L_z = m \hbar\), where \(\ell = 2\) and \(m = 1\), calculate the expectation values \(\langle L_x \rangle\), \(\langle L_y \rangle\)... | 35,736 | cqadupstack-physics |
105635 | Which values of the Riemann zeta funtion at negative arguments come up in physics? | For my bachelor's thesis, I am investigating Divergent Series. Apart from the mathematical theory behind them (which I find fascinating), I am also interested in their applications in physics. Currently, I am studying the divergent series that arise when considering the Riemann zeta function at negative arguments. The ... | What are some specific examples of divergent series that have applications in physics, and can you explain the contexts in which they arise? Additionally, which summation methods are used for these series, and are there any notable divergent series that have proven resistant to summation by current methods in physics o... | 10,455 | cqadupstack-physics |
83789 | Intuitively Re-Deriving Equations of Mathematical Physics | Using the intuitive interpretation of the Laplacian $\vec{\nabla}^2$ as the difference between the average value of a field in the neighbourhood of a point & the value of the field at that point, one can pretty easily & quickly derive the form of the heat equation, Poisson's equation & the wave equation (as is done in ... | Using the intuitive interpretation of the Laplacian as the difference between the average value of a field in the neighborhood of a point and the value of the field at that point, can you derive the form of the Helmholtz equation and explain how this intuition informs the relationship between wave propagation and the s... | 14,681 | cqadupstack-physics |
92753 | energy difference uniqueness in hydrogen atom | Is the energy difference between two energy levels unique for that particular pair of levels for a hydrogen atom ? If so how can one prove it? | What is the formula to calculate the energy difference between two specific energy levels in a hydrogen atom, and how can this relationship be demonstrated experimentally? | 24,420 | cqadupstack-physics |
28963 | Carrying water on person, or on the frame when bicycling | So, the question is as follows: What is the difference in work exerted by the rider in the two following scenarios? a) Rider + bike. Water carried in a holder on the frame b) Rider + bike. Water carried in a backpack (for simplicity, assumption that weight of holder = weight of backpack and backpack is perfectly aero... | Calculate the difference in work done by a rider while cycling with a water holder mounted on the bike frame versus carrying a water backpack. Assume both scenarios involve the same total weight of water and that the holder's weight is equal to that of the backpack. Determine which scenario requires more work based on ... | 24,382 | cqadupstack-physics |
28665 | Measure the voltage of a resistor without error | We have a simple circuit given, a resistor $R_x$ and a fixed current source with $I = 50 \, \mathrm{\mu A}$. Now over the resistor there is a currentmeter which has an internal resistance. In any case some of the current will go through the currentmeter and therefore the result will be slightly off. The question asks u... | How can you modify a circuit with a fixed current source of \( I = 50 \, \mathrm{\mu A} \) and a resistor \( R_x \) to avoid measurement error when using a current meter with an internal resistance, without simply replacing the current meter with one of higher internal resistance? | 27,791 | cqadupstack-physics |
107477 | Question about buoyancy | I took an empty clear sphere with radius r, put some weight inside this sphere, and put in into the water. I calculate the buoyancy force as: Volume of the sphere = Volume of the water displaced (Vdisplaced) = (4/3) _pi_ (r^3); Weight of the displaced water = Buoyancy force (B) = Vdisplaced * density of water; Wtotal= ... | What is the condition for the buoyancy force to overcome the total weight of a clear sphere filled with weight and air, given that the radius of the sphere is \( r \) and the density of water is \( \rho \)? Also, can you explain how the air inside the sphere affects its overall density and buoyancy? | 32,058 | cqadupstack-physics |
17575 | Determining the capacitance of a system with a non-homogenous dielectric | In an experiment we were given non-homogenous dielectric substances described by functions of coordinate. How can capacitance be determined from this? | How can you calculate the capacitance of a capacitor filled with a non-homogeneous dielectric material described by a spatially varying dielectric function ε(r)? | 32,495 | cqadupstack-physics |
77561 | $\mathrm{Tr}(XY) = \mathrm{Tr}(YX)$? | I'm trying to understand the Dirac notation to understand quantum mechanics better. I'm trying to show the above relation using the Dirac notation. Given $$\mathrm{Tr}(X)~=~\sum_j\langle j|X|j\rangle$$ and $$\mathrm{Tr}(Y)~=~\sum_j\langle j|Y|j\rangle.$$ Thus,$$\mathrm{Tr}(XY)~=~\sum_{ij}\langle j|X|i\rangle \langle i|... | Given two operators \( X \) and \( Y \) in a Hilbert space such that \( XY \neq YX \), calculate the trace of the product \( \mathrm{Tr}(XY) \) using the provided Dirac notation expressions. Specifically, express \( \mathrm{Tr}(XY) \) in terms of the sums over basis states \( |j\rangle \). What is the relationship betw... | 4,920 | cqadupstack-physics |
74829 | Differences the nonlinerarties | I want to comparison between oscillons based on non-linearities. Can someone elaborate it with the reason behind it : > When the sinusoidal vibrations are of the correct amplitude and frequency > and the layer of sufficient thickness, a localized wave, referred to as an > oscillon. > > Astonishingly, oscillons of oppos... | What is the quantitative relationship between the amplitude and frequency of sinusoidal vibrations required to create oscillons in a medium of a specific thickness, and how does this affect their ability to form bonded pairs versus repelling each other? | 35,553 | cqadupstack-physics |
101739 | Why tritium doesn't undergo $\beta^-$ decay to form $He^3$? | In my textbook it is written that Tritium is an isotope of hydrogen whose nucleus Triton contains 2 neutrons and 1 proton. Free neutrons decay into p + electron + anti-neutrino . If one of the neutrons in Triton decays, it would transform into $He^3$ nucleus. This does not happen and the reason is given to be that both... | Why must both neutrons in the Triton nucleus decay simultaneously in order to avoid forming a helium-3 (\(He^3\)) nucleus, and what would happen if only one of the neutrons decayed? | 37,285 | cqadupstack-physics |
108435 | Does timbre consist in pitch and volume? | I read that the physical properties of a sound wave correspond to its audible qualities: pitch, volume, and timbre. However, an oscilloscope uses only two- dimensions to accurately depict the physical properties of a wave. Intuitively, pitch and volume seem more basic than timbre does, so I surmise that timbre must con... | How can an oscilloscope's two-dimensional waveform representation capture the three properties of sound—pitch, volume, and timbre—while providing a quantitative analysis? | 17,420 | cqadupstack-physics |
23138 | Is the efficiency of a stirling engine affected by dead volumes? | Consider the p-V diagrams of an ideal and real stirling cycle, as found here The article suggests that dead volumes reduce the efficiency of a stirling engine. On the other hand, a simple thought experiment that comparas an ideal stilring engine A with a bigger real stirling engine B, where B has dead volumes so the am... | In a Stirling engine, if the dead volume is increased while keeping the amount of working fluid constant, how does this affect the thermal efficiency and power output of the engine, and what specific quantitative relationships can be determined from the p-V diagram for both the ideal and real Stirling cycles? | 26,346 | cqadupstack-physics |
123262 | $\theta '' = \frac{a}{R}$? |  Assume that this is a general circular motion where $\theta$ is a function of time. I've derived some equations below and found that the angular velocity in the end is zero. Which step of my derivation is wrong? $ \vec{p}(t) = R cos(\theta) \hat{x} +... | In a system undergoing uniform circular motion, the angular position \(\theta\) is a function of time. If the angular velocity is defined as \(\dot{\theta}\) and the tangential acceleration is given by \(a_t = R \ddot{\theta}\), where \(R\) is the radius, under what conditions does the equation \(\frac{a^2}{R^2} = \dot... | 25,029 | cqadupstack-physics |
11268 | Derivation of the oil drop experiment | The oil drop experiment performed by Robert Millikan in 1909 enables us to calculate the elementary charge. The following forces have effect on the droplet: 1. $F_\mathrm{G} = m g = \frac{4}{3} \, \pi r^3 \rho_\mathrm{Oil} g$ 2. $F_\mathrm{A} = \frac{4}{3} \, \pi r^3 \rho_\mathrm{Air} g$ 3. $F_\mathrm{E} = q E = ... | What are the steps to calculate the elementary charge using the formula $$q = \frac{9 \pi d}{2 U} \sqrt{\frac{\eta^3 (v_1 - v_2)}{\rho^* g}} (v_1 + v_2)$$ derived from the forces acting on an oil droplet in Millikan's oil drop experiment? | 35,923 | cqadupstack-physics |
51788 | What does the quantum state of a system tell us about itself? | > _In quantum mechanics, quantum state refers to the state of a quantum > system. A quantum state is given as a vector in a vector space, called the > state vector. The state vector theoretically contains statistical > information about the quantum system._ The article in Wikipedia about quantum state suggests that the... | What are the specific statistical properties represented in a quantum state vector, and how do they relate to the measurements of position, momentum, and energy for a quantum particle such as an electron? | 3,007 | cqadupstack-physics |
62059 | Why frequency and tension doesn't change in the two medium? | I am reading a book about wave mechanics. There are two different cord (one light and one heavy) connected together, one person waving the lighter one, the wave transverse to the right from the lighter one to the heavy one. The frequency and the wavelength is given so the speed and the tension of the lighter cord are u... | In a wave mechanics experiment, a lighter cord and a heavier cord are connected. When a wave travels from the lighter cord to the heavier cord, it is noted that the tension and frequency remain unchanged, while the wavelength does change. If the frequency of the wave is 200 Hz and the speed in the lighter cord is found... | 28,136 | cqadupstack-physics |
15434 | Literature Request: Introduction to d-wave superconductivity | I'm looking for a pedagogic introduction to d-wave superconductivity. Ideally, this would involve a derivation of d-wave superconductivity and the form of the gap parameter from some fundamental Hamiltonian (if such a derivation is even possible). Books and papers are welcome. | What is the mathematical expression for the d-wave gap parameter in the context of d-wave superconductivity, and can you provide a simplified derivation from the Bardeen-Cooper-Schrieffer (BCS) Hamiltonian? | 12,767 | cqadupstack-physics |
47312 | Why is lightning more rare during snow storms than rain storms? | Lightning and thunder during a snow storm is uncommon. As far as I know, more uncommon than during a typical rain storm. Why is this? I speculate it might be one, or both, of the following two ideas, one having to do with a change in the dielectric, the other having to do with a change in the catalyst. | What are the differences in the dielectric properties of snow compared to rain, and how do these differences affect the occurrence of electrical phenomena such as lightning during storms? Please provide specific measurements or properties to support your answer. | 26,109 | cqadupstack-physics |
18062 | How do electromagnetic waves carry quantised energy? | If an electron oscillates about a mean position, it will create a time varying electric filed which in turn will create a time varying magnetic field and so on to create an electromagnetic wave. How does this wave carry energy , in which amount and how can this be quantised? I know that energy is quantised when we see ... | What is the expression for the energy carried by an electromagnetic wave in terms of its electric and magnetic field strengths, and how can this energy be quantized using Planck's relation? | 36,788 | cqadupstack-physics |
55318 | Where does energy go in destructive interference? | I have read that when two light waves interfere destructively, the energy contained within is transferred to other parts of the wave which have interfered constructively. However, I am having some trouble grasping this. While in experiments such as Young's Double Slit experiment, there are visible bright bands of highe... | In the context of wave interference, is it possible to configure two light waves to interact such that they only interfere destructively and do not create any regions of constructive interference? If such an arrangement is theoretically feasible, how is the energy transferred between the regions of the wave that interf... | 3,575 | cqadupstack-physics |
129538 | Why does magnetic field increase when the number of coil turns increase? | Since we all know that to increase the magnetic field we can do these of the following things: (i) Increase the number of turns in a coil, (ii) Increase the current following through conductor, and there would be more but I know only these (upto my standard - Xth ) now if I use the first method to increase the magnetic... | If I increase the number of turns in a coil by adding an additional length of conductor that increases the resistance by \( x \Omega \), and the resulting current decreases by \( x \) Amperes due to Ohm's law, how can we calculate the net change in the magnetic field produced by this coil compared to its original state... | 31,860 | cqadupstack-physics |
20734 | The maths/physics in "The Amazing Spider Man" | > **Possible Duplicate:** > What does Peter Parkers formula represent? I just saw the trailer for the new Spider Man movie and couldn't help but notice the image after the guy says "How did you come up with this". So here is a transcript (the last part can't be seen): $$\eqalign{ & \frac{{d\log \Phi }}{{dt}} = \alph... | What does the equation $$\frac{{d\log \Phi }}{{dt}} = \alpha \left( {1 - g{{\left( {\frac{\Phi }{k}} \right)}^\beta }} \right)$$ represent in terms of biological or physical processes, and how does it relate to concepts such as the thermodynamic partition function? | 31,052 | cqadupstack-physics |
97936 | Hawking evaporation is due to NEGATIVE mass? | So I have seen an animation about Stephen Hawking (after his recent study state universes claim) that Hawking evaporation is due to negative mass; But how is this possible? I mean, there is no such thing as negative mass! | What are the implications of negative mass in theoretical physics, and can you provide an example of a scenario where negative mass could conceptually exist, even if it is not currently observed in nature? | 8,128 | cqadupstack-physics |
93905 | Symmetries for an inertial frame | According to Noether's theorem, a symmetry of space-time w.r.t. an observer, will yield a corresponding conservation law for a closed system w.r.t. that observer. Now if our space-time has 3 symmetries w.r.t. an inertial observer namely isotropy and homogeneity of space and homogeneity of time, so only 3 conservation l... | If we have a quantity defined as \( Q = \vec{r} \cdot (\vec{r} \times \vec{f}) \), where \( \vec{r} \) is the position vector and \( \vec{f} \) is a force vector in a closed system, what conditions must be met for the time derivative \( \frac{dQ}{dt} \) to be equal to zero, indicating that \( Q \) is conserved? Also, w... | 22,360 | cqadupstack-physics |
96308 | Twisted supermultiplets | What is a twisted supermultiplet, in a generic supersymmetric theory? Which ordinary fields belong to one of such twisted supermultiplets? I am confident with the idea of a supermultiplet or a superfield, in $\mathcal{N}=1,2,4$. However, I don't know what the term _twisted_ stands for. Also, why is it useful to conside... | In the context of supersymmetric theories, can you define a twisted supermultiplet and identify which ordinary fields belong to one of these twisted supermultiplets? Additionally, explain the significance of considering twisted supermultiplets in theoretical physics. | 2,633 | cqadupstack-physics |
101342 | How to obtain Maxwell's Lagrangian from complex scalar fields? | I've looked in several books and they all show how to obtain electrical interactions by forcing local gauge invariance of any complex scalar field Lagrangian (like Klein-Gordon or Dirac). I manage to separate the new Lagrangian into the original one (the free Lagrangian) and the interaction part of it. But how I get Ma... | How can the term \( F^{\mu\nu} F_{\mu\nu} \) be derived in the context of gauge invariance when obtaining Maxwell's Lagrangian from a complex scalar field Lagrangian? | 2,845 | cqadupstack-physics |
27742 | Paper listing known Seiberg-dual pairs of N=1 gauge theories | Is there a nice list of known Seiberg-dual pairs somewhere? There are so many papers from the middle 1990s but I do not find comprehensive review. Could you suggest a reference? Seiberg's original paper is this Inspire entry and its cited by these papers, but I do not know of any summary of the information in these 100... | What is the total number of known Seiberg-dual pairs that have been identified since the original paper by Seiberg, and can you provide a comprehensive reference or summary of these pairs? | 22,765 | cqadupstack-physics |
33176 | Why does a photograph of a face look like it is always watching you? | Imagine a photo that is taken of someone looking straight at the camera. Why when we look at the photo now _from any direction_ it looks as if the person is looking straight at us? | What property of perspective allows a photograph of a person looking straight at the camera to make it appear as though they are looking at you, regardless of your angle of view? | 18,712 | cqadupstack-physics |
24245 | Entanglement spectrum | What does it mean by the _entanglement spectrum_ of a quantum system? A brief introduction and a few key references would be appreciated. | What is the entanglement spectrum of a quantum system, and how can you calculate it for a bipartite quantum state represented by a density matrix? | 10,611 | cqadupstack-physics |
22182 | Can the mass of longitudinal and transverse W bosons be measured separately? | Some higgsless unified models of particle physics predict that the mass of longitudinally polarized W bosons and the mass of transversely polarized W bosons are different. In those models, a difference in masses is also predicted to appear for the Z boson. Is there a way that the existing data from the LHC, the LEP or ... | What measurements or analyses have been conducted using existing data from the LHC, LEP, or Tevatron to determine whether the masses of longitudinally polarized W bosons and transversely polarized W bosons—and the Z boson—differ, in accordance with predictions from higgsless unified models of particle physics? | 31,929 | cqadupstack-physics |
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