# All Questions

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### Angular Momentum Addition in Phase Space QM

In my very limited understanding of geometric quantization, we quantize spin by choosing as our phase space $S^2$ with a suitably normalized area form as the symplectic form. Depending on the ...
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### Tension in string and gravitational force on bob relative strength

When calculating time period of simple pendulum (an approximation of SHM at small amplitudes) we take gravitational force greater than tension in string and resolve gravitational force in two ...
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### Can the internal energy of an ideal gas system increase as temperature decreases?

If change in $\Delta U = Q + W$ Then adding $x$ moles of an ideal gas of lower temperature into a system of internal energy $U$ would increase $U$ as the kinetic energies of the molecules of the ...
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### Why is there not always a force in the direction of motion?

This was a question on a physics competition. A girl throws a teddy bear straight up. Consider the motion of the bear only after it has left the girl’s hand but before it touches the ground, and ...
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### Cherenkov radiation can it happen in a jar using tap water with 8 thorium laced lantern mantles as a radiation source

I placed 10 thorium laced lantern mantles into a wide mouth glass jar 5.25 inches diameter x 6 inches tall, filled with tap water to just below the threaded neck portion of the jar. The jar mouth ...
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### $dU = \sum E_i dp_i + \sum dE_i p_i = TdS - PdV \implies \sum dE_i p_i = - PdV$?

This is a formula my professor gave in class, but I'm entirely lost how he arrived at the conclusion (I understand the assumption). Could anyone help me?
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### How is electric field effected by loss of energy of charge?

Recently, I asked a question related to energy of a charge(This is the question). In one of the answers, in the comments section, I got an answer that the strength of the electric field is lessened ...
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### Understanding parallel plate capacitors

I need help with understanding this assignment. I originally though of using the equation of Eo*A/D = Q/ΔV but I don't know how to answer this without actual numbers to plug in besides the epsilon-not ...
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### What is the meaning of Boltzmann definition of Entropy?

I would like to ask if someone knows the physical meaning of Boltzmann's definition of entropy. of course the formula is pretty straightforward $$S=K_b\ln(Ω)$$ but what in the heck is the natural ...
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### Temperature change in Adiabatic stretching of liquid film

The first law applied to a liquid film is $dU = dQ +2\sigma dA$ where $\sigma$ stands for surface tension. Or $dQ = dU + (-2\sigma) dA \leftrightarrow dQ = dU + PdV$ Now suppose we wish to find ...
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### Rutherford scattering: question about impact parameter

http://wonka.physics.ncsu.edu/~blondin/py203/HW5solns.pdf I have a question about the solution to a problem I found online. I don't understand why the author plugs in $\theta=90$ when the question is ...
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### Dielectric Constant and Frequency

How dielectric constant of a parallel plate capacitor varies by varying frequency in physical terms?
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### Intuitive explanation of $1/2(at^2)$ motion equation?

The full equation $$Xf = X_o + V_o t + \frac{at^2}{2}$$ is integrated from the velocity function (which was integrated from constant acceleration function), right? The problem is, I can't seem to ...
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### Scattering amplitude Green's function integral

On page 208 of Weinberg's QM book, he calculates the following integral \begin{align} G_k (\vec{x}-\vec{y}) =& \int \frac{d^3 q}{(2\pi \hbar)^3} \frac{e^{i\vec{q} \cdot (\vec{x}-\vec{y})}} ...
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### How to calculate power necessary generated from wind turbine to run a motor

I was making a small/cheap wind turbine, and I am stuck on how to calculate the power needed (speed of wind) to run a brushed motor (since I figured that would be the easiest to run with rotor blades ...
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### Magnitude of the average velocity vector (not the average speed)

Thank you ahead of time for taking to look at this. For this following problem we were given an answer however I am almost positive the given answer is wrong. It doesn't even make sense. So here is ...
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### Good books on elasticity

Can someone suggest good books/textbooks/treatises/etc on elasticity?
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### A block floating on water is pushed inside until it touches the bottom. Will the block come back? [duplicate]

A block floating on water contained in a vessel is pushed inside until it touches the bottom of the vessel and then released. Will the block come back? Bouyant force acts because the pressure on ...
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### Sign of Wick rotation

Suppose you have the integral $$i \int^\infty_{-\infty} L_M(t) dt$$ and that $L_M$ contains two poles: when $t>0$ the pole lies above the t-axis and when $t<0$ the poles lies below the t-axis. ...
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### Time Dilation and the direct opposite

// I just looked this up in google 30 kilometers per second Thus, the surface of the earth at the equator moves at a speed of 460 meters per second--or roughly 1,000 miles per hour. As ...
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### Could Dark Matter Exist Prior to the Big Bang? [on hold]

Recent discoveries that the universe is accelerating in its expansion has made me consider the possibility that dark matter might have existed prior to the time the universe sprang into existence, ...
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### Optical signals and the electromagnetic spectrum

Are Optical signals are not considered part of the E-M spectrum? Or are they?
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### Work and free body diagrams

I am a bit confused with how to find work when there is a free body diagram. I am trying to work out this problem, and in it a box is being pulled at a constant speed by a rope at a constant angle ...
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### Calculating the data rate for a baud signal

I have been working on these questions for the past few hours. I am working on calculating the data rate of baud signals, where each symbol can take on one of two levels. I wanted to know if I have ...
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### Work by Gravity using Tensors

Now I'm familiar with the various methods for deriving work done by gravity, but I noticed a few things about the situation, and wanted to see if I could properly apply a tensor treatment to the ...
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### Bending of light

Why does bending of light(diffraction) occur?
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### Why does magnetic field and not electric field invert in a reflection? (related to another question)

When you are talking about an elctromagnetic wave that reflects on a surface (for example here), why do you say that the reflected magnetic field inverts and not the electric field? \begin{align} E_+ ...