# All Questions

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### Which symmetries lead to the ladder operators of the harmonic oscillator

It seems like symmetries usually lead to ladder operators. For example in a central potential problems the conservation of angular momentum leads to angular momentum ladder operators being used in the ...
• 320
1 vote
16 views

### Moment of Inertia of cube about the axis along one of its diagonal

How can we find Moment of Inertia of a solid as well as a hollow cube about the axis passing from one of its diagonal? I tried really hard solving it, please guide me to the solution.
1 vote
24 views

### In which direction is the relation between the time-component of celerity and the Lorentz factor defined?

Celerity (a.k.a. four-velocity) is defined as $w^\alpha=\frac{\mathrm{d}X^\alpha}{\mathrm{d}\tau}$, where $\mathrm{d}X^\alpha=(\mathrm{d}t,\mathrm{d}x,\mathrm{d}y,\mathrm{d}z)$ and $\mathrm{d}\tau$ is ...
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### Distributing 3 distinct particles among 4 distinct energy states

If we consider the following state of the above mentioned system with energy 5: $$\{|x_1x_2||x_3\}$$ Where, 2 particles occupy the state $E_1$ with energy 1 and 1 particle occupies state $E_3$ with ...
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### Symmetry group and dualities

Let's say two quantum models $M_1$ and $M_2$ are dual to each other and let their symmetry groups be $S_1$ and $S_2$ respectively. Is it necessary for $S_1$ to be isomorphic to $S_2$? (I thought so ...
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19 views

### Can the eye lens not produce a virtual image when the object is between Focus and Optical Centre?

My teacher dismissed the question saying it is not possible for the eye to do so simply because we didn't know the focal length of the eye. That confused me. The focal length can vary, sure. When we ...
• 351
1 vote
39 views

### Why can't thin clouds form rainbows?

Sunlight easily passes through THIN layers of clouds, composed of small water droplets/vapor, what is the problem accounted by the light rays that they are not able to form a rainbow?
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### Confusion about Derivation for Bragg's Law/Condition

I am currently learning about Bragg's Law and its derivation. However, the assumptions/logic behind the derivation seems flawed to me. It is probably likely that I am incorrectly understanding some of ...
1 vote
28 views

### What are the differences of Scalar and Pseudoscalar Yukawa Theory?

I know that some polarized interactions are forbidden. But for unpolarized (summed over incoming and outgoing spins), are the amplitudes and decay rates of a Yukawa scalar and pseudoscalar coupled to ...
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33 views

### Why does cutting a solenoid into half reduce its magntic properties

Cutting a solenoid is said to reduce its magnetic properties. Is this change attributed to its magnetic moment or to its magnetic field. Magnetic field of the solenoid could be same because the turn/...
39 views

### Closing Door on a Moving Car [closed]

I am working a problem from the 3rd edition of Goldstein's Classical Mechanics (problem 5.23): An automobile is started from rest with one of its doors initially at right angles. If the hinges of the ...
73 views

### In equation (20) from lecture 10 in Leonard Susskind’s ‘Classical Mechanics’, why is there a summation involved?

Here is the equation $$\{x_i,L_j\}=\sum\limits_{k}ϵ_{ijk} x_k.$$ Is this equation generalised for any number of dimensions? In which case, would the following example be correct assuming 4 dimensions? ...
28 views

### Do quantum fluctuations follow Hamilton's principle? [closed]

I already asked a related question yesterday (Equation of motion of quantum fluctuations/ quasi particles), but i did not get any satisfying answer. My question is simple: Do quantum fluctuations ...
• 13
46 views

### GRAVITOELECTROMAGNETISM [closed]

Has anyone here worked on approximate theories of gravitation, such as GEM? If I hypothesize the existence of a field dual to the gravitational one, similar to how the magnetic field is dual to the ...
30 views

### Contradiction in the Carnot Cycle?

The carnot cycle is reversible, because the temperature difference between heat reservoir and fluid is extremely low, so that heat can flow in both directions. Also, the carnot cycle is described as ...
36 views

### Maxwell's equations in electromagnetic theory [closed]

At M.Sc physics or BS physics level a student should study Maxwell's equations with how much depth tell name of specific concept
46 views

### Is gravitational potential energy of body by $mgh$ negative? [closed]

Consider a 15kg object at 1m from earth ground level, is P.E = 15kg * 9.8m/s^2 * 1m = 147J or P.E = -Gm1m2/r^2 * h = -9.8 * 15kg * 1m= -147J after browsing for a while on debate of potential energy's ...
45 views

### Oblique Projectile Motion "HOMEWORK AND EXERCISES" [closed]

It is a multi-correct question. We have a body projected from the top of a tower with specific initial conditions. $V_\text{initial} = 9.8\,\text{m/s}$ $\text{Height} = 19.6\,\text m$
35 views

### Does the Earth's Magnetic Field Affect Sleeping Position? [closed]

Does the Earth's magnetic field affect the sleeping position of a person? For sleep experience with Nature sounds, check out this video: https://www.youtube.com/watch?v=5FzjrdiUr90
96 views

### What, exactly, does Schrödinger's wave equation describe (just in plain English, without any of the math please) [closed]

I've been studying the philosophical foundations of quantum mechanics and would love to find out if my understanding is correct. Could anyone please let me know if the below description is accurate? ...
56 views

### Does Mass Actually Displace Space-Time, or does Mass only Distort it?

1. Question Given the plethora of space-time illustrations, there is a sense that space-time is actually being displaced by mass, (planets). But on its face, this doesn't really make sense because ...
47 views

### Could Space-Time Displace or Distort Itself? [closed]

1. Question Could space-time distort and displace space-time? If space-time can interact with surrounding space-time, then which ...
20 views

### How to find permeability of a magnetic material?

I have been working with magnetic materials for quite some time now and never really explored this fundamental parameter. After looking through the literature I realize there and quite few different ...
50 views

### Topic : Classical Electrodynamics; Lienard wiechert potentials [closed]

So I have just finished studying the Lienard wiechert potentials for a moving charged particle. After doing some problems from Griffiths I stumbled upon some problem which as follows: An ...
1 vote
44 views

### How do you build a small-scale neutrino detector? [closed]

*This question is similar to: Is a DIY neutrino detector feasible?. The difference between my question, and the old one is that the question is from over 8 years ago. Naturally, some of the answers ...
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29 views

### Enthalpy at constant pressure/volume

Enthalpy is defined as the heat the goes into (leaves) a system at constant pressure. $dH =TdS+ d(PV) = TdS + PdV + VdP$ For some reason, most texts simply write $dH = TdS + VdP$ but haven't they ...
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### Lorentz transformation of Creation and Annihilation operators for a real scalar field theory - MIT OCW QFT I Problem set 3 [closed]

I have been working through the MIT OCW's QFT lecture notes and problem sets, but I have come to realize that I have a fundamental misunderstanding of what is meant by how objects transform under ...
51 views

### Does A Pivot Exert A Force

On a frictionless horizontal table, a uniform stick is pivoted at its middle, and a ball collides elastically with one end, as shown in Fig. 8.10. During the collision, what are all the quantities ...
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54 views

### Parametric down-conversion - QFT necessary?

In quantum optics, one ususally starts by quantizing the free electric field and obtains an expression for the electric field operators:  E(\vec{r},t) = \sum_{\vec{k},p} C_{\vec{k}} \vec{e}_{\vec{k},...
• 21
1 vote
38 views

### Entanglement distance and quantum mechanics length scales

In this answer https://physics.stackexchange.com/a/9253/256311, the author said Usually, we think of quantum mechanics to govern the microscopic world, involving length scales of under a micrometer, ...
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49 views

### Why particle is certain to escape the conservative field when the mechanical energy is positive?

It is generally said that the particle is bound into the conservative field when the mechanical energy is negative and zero is the limiting case and the particle will escape the field when the ...
1 vote
40 views

### Drake Equation with Random Walks

Goal I'd like to use the Drake Equation with random walk theory to estimate the probability of aliens reaching Earth. Drake Equation The Drake Equation estimates the number of advanced civilizations ...
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### Explanation between the potential energy of a charge and the electric force experienced by a charge

Suppose there are two opposite charges and an infinite distance between the two. At this initial point, the electric potential energy of the two charges and the electric force experienced by each ...
45 views

### What is the frequency of a standing wave? [closed]

I understand that constructive interference of waves results in standing waves. And for a wire with both ends fixed the frequency should match the fundamental frequency of the wire to produce standing ...
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