# All Questions

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### Optical signal filters

Are there any optical filters which filter the signal's frequency and not based on the wavelength of the light? So what I mean is, if I have a modulated/pulsating light signal riding on a large DC ...
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### Liquid Column “Recoils” in a Sealed Cylinder When Hit by a Piston — Is it Possible?

Consider a cylinder filled partially with a liquid (e.g. water). The cylinder is sealed, and is at held at room temperature (e.g 298K). At equilibrium (or when no external disturbance is imparted to ...
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### Phase change in control mass question

Water has a critical specific volume of 0.003155 m3/kg. A closed and rigid steel tank of volume 0.025 m^3 contains a mixture of water and steam at 0.1 MPa. The mass of the mixture is 10 kg. The tank ...
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### Centre of mass, intergral

I was answering a question on proving the parallel axis thereom for angular momentum and came across this: $$\int Yy'dm=Y\int y' dm=0$$ Where the position of the center of mass of an object is given ...
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### How hard is ice?

I know that there are many different types of ice and many ways for ice to form but I want to know about ice that a human might typically encounter, i.e. from a freezer or a sub-zero environment ...
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### How to tell whether photons are entangled?

Suppose you have some sort of a "black box" system - you know nothing of its inner workings. The system has two outputs, let's call them A and B, and it occasionally emits photons - one photon from ...
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### Determining the moment of force

A force (F = 3i + 2j) passes through through a point P with respect to an origin O. How do I determine the moment of the force at the origin.
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### Special case of work done by two opposing forces of equal magnitude on a body possesing inertial motion

Consider an elevator moving upward with constant velocity. The constant velocity is maintained by an upward tensional force equal to weight. If we add the total work done on the elevator it will be ...
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### Why doesn't the light from galaxies appear stretched?

Maybe it's my ignorance of astrophysics/cosmology, but I have been wondering this: Why do galaxies not appear stretched when we observe them? Assuming a galaxy that we observe is 100,000 light years ...
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### Does Gravity Warp Coulomb's force?

Does gravity effect the "sphericalness" of the Coulomb force? For example, is the field 1 meter above a charge weaker than the field 1 meter below the charge? Could a 0.014% difference in the field ...
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### How to calculate the supporting force exerted by a stationary object (cupboard) and support (brackets) for it?

I have a wall mounted Stuva Ikea cupboard, which measures 60x64x30cm. The base is 64x30cm. It is already supported by 2 holes at the back base, (64x60cm). But I need to add in L shape brackets ...
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### Time reversal in Maxwell's electromagnetism [on hold]

The statement of the time-reversal invariance of Maxwell's electromagnetism, as I understand it, is the following. Given $\mathbf{E}(\mathbf{r},t)$ and $\mathbf{B}(\mathbf{r},t)$ that satisfy all ...
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### How can a glass rod become charged if it is an insulator?

I was reading some of the other questions, and I found this one about a glass rod and how it gains a net charge when rubbed with a silk scarf. I learned from working in a shop one summer that most ...
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### Is it possible for an electrical device to generate more heat than another using less power or the same?

People are claiming that a Plasma TV uses more power which explains why it uses more heat. We refer to power as wattage in this regard. Countering this, is it possible that a device can draw the same ...
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### Simple mechanics problem [on hold]

I have no idea how to approach this problem I drew the diagram but that hasn't helped that much.
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### Is there an equivalent to wetness for air?

I was wondering if there was something equivalent to the property of being wet with water, but with air instead. For example, if I drop water on my shirt, I'll notice by its appearance and feel that ...
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### Kinematic sign convention

For example, if I drop a ball from a $50$ meters building, then I will consider the ground is $0$ meter downward is positive ( which makes gravity positive, downward velocity positive, etc) so ...
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### Large wavelength limit of gluons

Does there exist a classical limit of QCD? I mean in the sense of wave particle duality of eg photons. Is there any similar thing for gluons?
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### Quantum Entanglement - an illusion based on a wrong assumption?

Almost all resources I've read about Quantum Entanglement speak about how 'amazing' it is that two entangled particles are bound over any distance, and that the state of one particle determines the ...
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### The intensity of the interference of multiple point spherical wave

I need to calculate intensity with all difference source such as velocity, amplitude, phase etc. I know the first equation and the intensity of the interference of two source with same value. By the ...
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### Need help in identification of formula [on hold]

i would greatly appreciate it if someone could provide me with the concept to learn about this equation
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### Lie theory and particle physics [duplicate]

I have recently been reading Intro to Lie algebras and representation theory by Humphreys, and when I am finished I am interested in reading about Lie groups and Lie algebras and their applications to ...
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### What is the electromagnetic field and what is the Higgs field?

I have several questions regarding the electromagnetic field and Higgs field which are connected, so I thought I would ask them together. Would be grateful for any information on any of the questions: ...
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### Looking for a simple proof of symmetry of linear susceptibility tensor

Getting a diagonal susceptibility tensor: Define the linear susceptibility tensor as $\chi_{ij}$: $P_i = \epsilon_0\chi_{ij}E_j$, using standard notation for the electric field and the polarization. ...
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### Effect of Reynolds number on wake region

For a flow over a smooth sphere, does the wake region increases with increase in Reynolds number? And if so, then why?
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### Is “scalar electromagnetics” real science?

This page claims that original Maxwell's equations, when formulated by Maxwell himself in quaternion form, had some special scalar part of electromagnetic field, which somehow appeared to describe ...
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### Is the flow in a ducted fan really incompressible?

I have a long duct with a fan in the middle of it. The fan causes a steady airflow in the pipe which is at low speeds (incompressible) the mean flow in the pipe is about 10 m/s. However the fan blades ...
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### Effective Field Theory (EFT) decoupling top

The decoupling theorem of Appelquist-Carazzone says that if you want to decouple a particle, the low energy resulting theory need to be renormalizable. You can't do that for the top, because you break ...
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### How to calculate electric force between two tubes?

Let's say the electric field due to a charged tube is $E$,length of the charged tube is $l$, radius is $r$ and the surface charge density is $\lambda$. I know that to calculate the electric force ...
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### Is Fourier's law of conduction a consequence of the second principle?

In classical thermodynamics courses, entropy is often motivated by the need to justify that heat flows from high temperatures zones to lower temperatures zones: this is seen as a consequence of ...
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### Interference and energy question here

So Im reading this material on interference and I noted the following sentence : During the interference of the light of two coherent light sources,the intensity of the radiation changes ...
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### Possible Error in deriving conformal generator

My professor gave me the following derivation for the full generator of the Lorentz transformations. The starting point is to consider a subgroup of the conformal group that leaves the origin fixed ...
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### Does the bolt really rise upward?

In this site,when the elevator rises up,the bolt falls downward under the force of gravity . But when distance is measured it is shown that it rises up,velocity becomes 0 & then it falls with ...
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### Direction of compass needle nearby an electric wire

Let through a straight wire flow an electric current. Using a compass needle how the needles tip will be directed to the wire? What happens when we switch the current direction and approach the needle ...
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### Any ket as a sum of eigenkets of a given observable

Most quantum mechanics texts include a phrase such as 'any ket can be written as a sum of eigenkets of a given observable'. I have problems with the generalities of any ket. Does this literally mean ...
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### Spherical coordinate versor problem [migrated]

I have to calculate $$i_\rho \times i_\phi$$ it should be $$i_\theta$$ but in my notes I have $$- i _\theta$$ Which one is correct? How can I do this kind of operations without mistakes?
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### Proof that total derivative is the only function that can be added to Lagrangian without changing the eom

So I was reading this: Invariance of Lagrange on addition of total time derivative of a function of coordiantes and time and while the answers for the first question are good, nobody gave much ...
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### Asymmetry in magnetic field direction of an electric wire

The simplest magnetic field is that of an infinitely long wire with uniform current. It does enjoy radial symmetry about the wire and has the variation as 1/r. To find the direction of the resulting ...