# All Questions

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### Has Dirac ever co-authored a paper? [on hold]

Just curious. Not counting PhD theses, books, and review papers, but regular research papers with original ideas.
158 views

### How does electrostatic force affect electronic devices?

How does electrostatic force generated by two seperate plates having opposite charges affect electronic devices? I know that magnetic fields have some harmful effects to electronic devices but I am ...
7k views

### Why can we see through rain?

I am gazing through my office window into a heavy rain. I am thinking that raindrops are like small lenses that bend the light. Thus I am surprised, that I can clearly see other buildings through the ...
41 views

### The action of a relativistic point particle, the meaning of its parametrization invariance and possible potential terms

i am currently toying around with the behaviour of a classical relativistic point particle a bit. For a free one we get the action \begin{align} S =\int_\tau - m\sqrt{- \dot X_\mu \dot X^\mu}. ...
51 views

### How to determine the observables rigorously?

In Quantum Mechanics, as I know, if a system is described by a Hilbert space $\mathcal{H}$, each physical quantity is associated with some hermitian operator $A : U\subset \mathcal{H}\to \mathcal{H}$ ...
15 views

### Book with solved problems on thermodynamics

I am working on honing my engineering thermodynamics problem solving skills at the undergraduate and graduate level. It would be much help if you could suggest me some good books with solved ...
4 views

### Problem with a phase space integral involving hypergeometric functions

In the evaluation of a phase space integral using tripole factorization (introduced here: http://arxiv.org/abs/hep-ph/0311276) I stumbled upon this integral \begin{align} ...
134 views

### Is the fundamental representation of $SU(3)$ irreducible?

I want to check if the fundamental representation of $SU(3)$ is irreducible. The algebra is $$\mathbb{su}(3) = \{ m \in Mat(3,\mathbb{C} )\ |\ m = -m^+,\ Tr[m] = 0 \}$$ and I've found the generators. ...
16 views

### How much force through a pulley

I have a tripod to lift a load out of a hole, which says its maximum working weight is 300kg. The load I need to lift is 200kg. I'm going to lift by a rope running through a pulley attached to the ...
11 views

### Observable Universe from two different perspectives

My layman understanding is that the universe is much bigger than that we can observe however due to the cosmological constant the observable universe is the matter etc. that is not moving away from us ...
33 views

### Compton's formula for change in wavelength

I want to measure the shift in wavelength predicted by Compton's formula. I find that I cant measure a shift of less than 5% and that I also cannot measure at angles greater than 150 degrees. What is ...
19 views

### How is d^2x/dt^2 derived and how can it be used to solve this? [on hold]

If, $\dfrac{d^2x}{dt^2} = -16x$ When $t= 0, v = 10$ and $x = 0$, where $x$ is displacement and $v$ is velocity. How would I obtain an expression for the velocity and displacement at time t? I am ...
861 views

### Do black holes violate the first law of thermodynamics?

When a black hole absorbs matter is it destroying that mass, thereby destroying energy, therefore violating the first law of thermodynamics?
16 views

### Proving a kinematics problem

I recently read in a book that the distance covered by an object projected vertically upwards in the last second of the upward motion is a constant independent of initial velocity.I tried to prove it ...
202 views

### Induced EMF of a rectangular loop should be zero?

Considering the shape of a rectangular loop in a changing magnetic field: The induced $\epsilon$ would be zero? Since a rectangular loop is a combination of wires in series to create such a shape. ...
13 views

### How to find the velocity of a fluid coming out of a pipe?

I need to know the velocity of the water coming out of a pipe and I know that I would need to know the Mass Flow Rate or Volume Flow Rate to find the velocity but my problem is that I don't know ...
75 views

97 views

### why doesn't liquid metal vaporize in a vacuum?

I am wondering why molten metal in a vacuum of electron beam and machines never turns to gas like liquid water does when exposed to a vacuum.
10 views

### Net force on magnet by fridge [on hold]

Dylan hangs a calendar on a refrigerator with a magnetic hook. Unfortunately, the magnet is too weak, so the magnet and calendar slide down the side of the refrigerator to the floor with an ...
32 views

### What do elements of CKM matrix imply?

In CKM matrix, there are 9 elements, e.g. Vud = .974, Vus = .227 ,Vub = .004. The sum of these 3 elements is greater than one, so they cannot represent the probability of an up quark to transform in ...
20 views

### Are orbits possible in de sitter space?

Since the de sitter space has constant positive curvature does that mean that objects can't orbit around other objects?
13 views

### Time period of bar pendulum

Why does the time period of a bar pendulum first decrease and then increase when the distance of the axis of rotation from the centre of gravity increases?
213 views

### Big Bang…or…Everywhere Stretch?

Recently I watched a minute-physics video that suggested that a better name for the beginning of time would be "Everywhere stretch" because there wasn't a space-time singularity that formed where the ...
33 views

### Proof of: if $\hat H | a_n\rangle=a_n|a_n\rangle$ then $f(\hat H)| a_n\rangle=f(a_n)|a_n\rangle$?

In Quantum Mechanics you have the eigenvalue equation: $$\hat H | a_n\rangle=a_n|a_n\rangle \tag{1}$$ where $\hat H$ is the Hamiltonian operator, $\{|a_n\rangle\}$ is a complete set of eigenstates ...
5 views

### Role of Mn in Perovskites

Good Day everyone!i don't if its the right site to ask this, but by the way, right now i'm searching for possible research in magnetoresistance properties of perovskite. So far, i already know the ...
24 views

### Deriving velocity after elastic and inelastic collision via the Principle of Least Action

I am reading on the Principle of Least Action from a historical perspective. I am also trying to make sense of it from a contemporary point of view -- though my training in contemporary physics is ...
4 views

### Stack exchange for Material Science [migrated]

i just want to know if there's a stack exchange for materials science topics? Since there are stack exchange for Biology, chemistry, Physics, Programming and many more how but materials science? ...
45 views

### With respect to the Casimir effect, why can't the wavelengths of the virtual particles between two plates just “pass through” the plates themselves?

I've read over the years that the suppression of many of the possible wavelengths between the two plates in a Casimir experiment is what causes the phenomenon (top comment on this Askscience thread is ...
### how can $\frac{kqq_o}{r}$ be $U$ for both a particle and a system of two particles?
If there is a charge $q$, at a distance $r$ from it there is a voltage and the potential energy of a test charge $q_o$ would be $\frac{kqq_o}{r}$. Now if I construct a system of two charges a ...