# All Questions

132,853 questions
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### Is the identity operator correspond to the observable which states the existence of system?

As it is claimed in this question, the identity operator is an hermitian operator, but not an observable. However, if I were to build a device, which only measures the existence of an electron in a ...
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### Application of Piezoelectric coefficients

Which piezoelectric coefficients are suitable for which application? For example, we know that high piezoelectric charge constant are used in generators and actuators.
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### What holds together an electron when it leaves valence?

Why doesn't it release all the photons in one shot? I am referring to both in the cathode ray tube and also in the vacuum of space.
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### Sig Figs in Coulomb's Law

Because Coulomb's constant only has 1 sig fig, should all of my answers have 1 sig fig when doing a problem with Coulomb's Law?
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### Question about solution to Morin Leaky Bucket problem

In Morin’s Mechanics book, a problem called leaky bucket goes: 5.17. Leaky bucket ** At $t = 0$, a massless bucket contains a mass $M$ of sand. It is connected to a wall by a massless spring with ...
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### Would Newton law of gravity be the same between two neutrons at smaller distance?

Imagine 2 neutrons placed at some distance apart, they should only gravitationally attract each other according to Newton law of gravity. Theoretically the law should work at smaller distance until ...
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### Magnetic flux changed by gauge transformation

This occurred to me when I was reviewing the Laughlin argument. Suppose a gauge transformation $A\rightarrow A+\nabla{\theta}$, where $\theta$ is the angle defined in a closed loop. When integrating ...
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### Is there a way to make an “unseeable monitor” without modifying a computer's hardware?

What happens if you remove the polarization filter from a computer monitor? shows how to make an "unseeable" monitor from a LCD monitor, i.e. one that requires special glasses to view. I was wondering ...
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### I was wondering how to calculate the energy of amplitude for electromagnetic waves [on hold]

in science class, we have to do slides on the different aspects of waves. I was wondering if anyone could explain to me how to find the energy of amplitude
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### Simple recoil calcuation: Difference in answer from Momentum vs Energy approach

I think I am completely misunderstanding a concept here. Depending on my approach, I get two different answers, which I shouldnt (as I understand)/ The Setup: A ...
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### Rotational motion of a spool [on hold]

A large spool of rope rolls on the ground with the end of the rope lying on the top edge of the spool. A person grabs the end of the rope and walks a distance, holding onto it, Fig. 8–64. The spool ...
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### Sound problems on frequency

Does frequency depend on the number of wavelength the source makes per second? Is it wavelengths? And what is the definition of amplitude?
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### Moment of Inertia of a cone rotating from its peak

How would you prove the moment of inertia of a cone rotating around from its peak about the y-axis? I've added a roughly drawn picture for better understanding.
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### When the barometer drops, my well level seems to rise - how?

I have a deep water well, with a length of 1/4" drip tubing, open at the bottom, taped to the pump 180' down. The other end of the tubing is connected to a gauge pressure sensor in the cabinet of my ...
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### Phase difference of waves [duplicate]

Why do light and sound waves under change in phase on reflection and is the change in phase for displacement and pressure wave the same in case of sound waves??
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### How much distance is there between electrons in an electron shell?

I imagine they would need keep a certain distance away from each other.
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### Is there a unified field?

Does the same force that holds the electron in orbit around the proton hold the Earth in orbit around the sun.
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### Big Bang, Entropy, Electromagnetic Radiation, Energy/Mass Equivalence, Gravity, General Relativity

If the photon in electromagnetic radiation does not have mass then does this mean that electromagnetic radiation is not subject to gravitational forces. Therefore it would continue at the speed of ...
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### Relativity- In a given Scenario, is FTL communication possible?

Take a black hole singularity of sufficient size that a planet could be placed in a stable orbit with a high amount of time dilation observed from the outside. Let’s assume it’s a pretty big black ...
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### Worked examples of Lie derivative [migrated]

I'm trying to find the Lie derivative of a 2 form $\sin(\theta)d\theta d\phi$ with respect to a vector field given in a differential basis and I think the way to go here is to use Cartan's formula but ...
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### Falling electric dipole contradicts equivalence principle?

Consider an electric dipole consisting of charges $q$ and $-q$, both of mass $m$, separated by a distance $d$. If the dipole is given an acceleration $a$ perpendicular to its moment the total ...
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### Is string theory inconsistent with the Standard Model of Elementary Particles?

According to (super)string theory, each fundamental particle represents a different vibrational mode of a relativistic string and each type of vibration pattern represents a different particle. But ...
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### How do all chemical reactions result in a product whose potential is less than the reactants if all reactions are not exothermic?

We are told by our chemistry teacher that all chemical reactions take place as reactants (that have bigger potential) change into products (that have smaller potential) hence instable substances ...
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### Static electric field

What mean: "An electric field (which is static) is not a source of energy (which comes from the electron), it is a 'store' of potential energy."
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### There are a component proportional to speed in gravitional force?

Reading some introductory texts to general theory of relativity (GR), I understand that the gravitational force between two objects has, in addition to the component in the direction of the vector ...
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### Discharging a photoconductor from the substrate side

Is it possible to discharge for example an OPC drum without exposing the surface? Since they are usually build on aluminum tubes (and belt type OPCs on metallized PET or other polymer) could one drop ...
The super-Poincare algebra contains supersymmetry generators $Q^I$ which satisfy fermionic anticommutation relations. By the higher-dimensional analogue of the spin-statistics theorem, they must ...
In $d = 3+1$ dimensions, the spin-statistics theorem states that fermionic particles have half-integer spin and bosonic particles have integer spin, in a well-behaved relativistic quantum field theory....