0
votes
0answers
37 views

Determining focal length and positions of principal planes

I have been stuck on this problem for a few days now, and I am still not confident which approach to take with this question. I am consider using the Gullstrand Equation, but I hear some of my ...
0
votes
1answer
41 views

Path of a swinging object on a rope [on hold]

With my lanyard in hand (weighted by my keys), a gentle swinging motion will put the keys in pendulum motion, swinging back and forth. Pendulum motion is relatively easy to model since it is ...
1
vote
0answers
29 views

Lamb shift and logarithmic corrections

Radiative corrections (Lamb shift) to the energy level (1S state) of a hydrogen atom can be written as a power series in $Z\alpha$ and $\ln(Z\alpha)$: $$\Delta E = \frac{\alpha}{\pi}(Z\alpha)^4 ...
0
votes
0answers
29 views

Showing the relationship between focal ratio and brightness [on hold]

I have an optics question that I have been stuck on for a few days now and I really need some guidance. Any help is appreciated! Question: The f-number (focal ratio) of a lens is the ratio of a focal ...
0
votes
1answer
16 views

Signal loss in non-reflected light through a tube proportional to square of the length?

Reading a patent I came across the claim: "...a portion of light intersecting the inner metal surface is not reflected, resulting in a loss in signal intensity... the signal loss is proportional to ...
0
votes
0answers
11 views

theoretical echo from a point scatterer

How can I compute an echo coming back from a point scatterer? Let's say I know the excitation signal (plane wave), scatterer position, medium properties, what else do I need to see, how the echo will ...
0
votes
3answers
35 views

Calculating released energy of a fission reaction

I have a question regarding the power of a fission reaction: You have a Uranium U235 atom, in which you send a neutron at to cause it to split into two (or more?) new cores. This reaction also sends ...
1
vote
0answers
13 views

Physics and mathematics books [duplicate]

I've just been accepted into Aeronautical engineering bachelors. Since I finished high school 2 years ago, I would like to refresh my memory on mathematics and physics. What would be some good books, ...
0
votes
0answers
44 views

Atom - light field coupling and emission process

Suppose a "2-state atom" and a light field are quantized with the following Hamiltonians, respectively: $$\hat{H}_A=\hbar\omega_{21}\hat{\sigma}^{\dagger}\hat{\sigma}$$ and ...
-1
votes
0answers
38 views

Is mass in the sub-atomic particles caused by their angular momentum? [on hold]

When they found the God Particle, they said it's responsible for creating mass in all other particles except photons and neutrinos. But how it creates mass is a mystery to me. My suspicion is that ...
2
votes
1answer
29 views

What is the momentum change in a Foucault pendulum?

From the wiki page: If the plane of swing was north-south at the outset, it is east-west one sidereal day later. This implies that there has been exchange of momentum; the Earth and the pendulum ...
1
vote
1answer
69 views

Adding cinnamon to my coffee makes it stop whirling much faster: Why is thats?

When I stir my coffee in a cup, the fluid spins a long time, but when I pour cinnamon into the cup, the spinning fluid slows and stops very rapidly - why?
0
votes
0answers
13 views

What could be the cause of a phase shift between the torque and the angular speed in DC generator?

Introducing some variations in the form of sinusoids in the electromagnetic flux of a DC generator connected to a hydraulic turbine runner I obtained some strange results for the phase shift between ...
-1
votes
1answer
46 views

Is liquid “air” (nitrogen, oxygen, aragon mixture) flammable?

I was wondering if liquid "air" (nitrogen, oxygen, and argon mixture) was flammable. Imagine you have a container. This container contains liquid air. The air is in liquid form, and is in direct ...
3
votes
1answer
61 views

Why can the bra and ket be varied independently?

Given a functional which depends on a function (ket), and its complex conjugate (bra), e.g. $$F[\varphi] = \langle \varphi|\hat{F}|\varphi\rangle = \int \varphi^{*}(\mathbf{r}) \hat{F} ...
2
votes
0answers
22 views

Which date the twin paradox was formulated first time? [migrated]

Any research about real measurements with faster moving than me systems - like GPS for example - leads to a mix of different sideway phenomenons like different gravitational potential on earth and in ...
2
votes
1answer
35 views

Gauss' Law and Electric Field Close to a Ball

So I've learned about Gauss' law and I have something in my head. Why does electric field that is very close to a ball is not close to infinity. Take a look at this image: As we can see, if we make ...
3
votes
1answer
48 views

How many photons are there in free space on average

Estimates of the amount of for example "dark matter" are of interest to the cosmologists. However, I have never seen an estimate of how many "free" photons could be speeding about in the known ...
1
vote
1answer
38 views

Action - Reaction?

I got to know that when a book is kept on a table. Earth attracts it due to Gravitational force. The book responds by attracting the earth with same force. (An action-reaction pair) The book is kept ...
0
votes
0answers
22 views

Deriving Wave Function for Scattering States with Delta-Function Potential

I am following the Griffiths Book on Quantum Mechanics, and am following the derivation for the wave function for Delta-Function Potentials. $$V(x) = -\alpha \delta(x)$$ In the scattering states, ...
32
votes
2answers
3k views

Cause for spikes in trinity bomb test

In Richard Rhodes' book, The Making of the Atomic Bomb, I was reading about the Trinity nuclear test. High speed photos were taken and this one is from <1ms after the detonation. The book mentions ...
-1
votes
1answer
32 views

Why am I not shocked when I touch a tree, and the tree touches a power line? [on hold]

Why am I not shocked when I touch a tree, and the tree touches a power line?
-2
votes
0answers
27 views

Downforce formula [on hold]

I need a formula force calcuating the down force generated by a NASCAR. I have done research and found some answers on google but i don't know what the formulas mean. So i was wondering if any body ...
2
votes
1answer
47 views

Can an absorbed photon be emitted as two photons?

I am taking an intro to astronomy class, and have touched upon absorption and emission lines and etc, the prof asked this question in class and got me thinking. I would want to say no, because one ...
1
vote
0answers
43 views

Question about the superconformal index

According to arXiv:1507.08553v1, the superconformal index, defined by $$I(\beta_j) = \mbox{Tr}_{\mathcal{H}}(-1)^F e^{-\gamma\{Q,Q^\dagger\}}e^{-\sum_{j}\beta_j t_j}$$ is independent of the ...
6
votes
1answer
103 views

Why is a stellarator-type nuclear fusion reactor so oddly-shaped?

My first impression: It's a mess. Why is it shaped like that? I can't find any info about its shape other than it's a special arrangement of magnetic coils. (link) Here's some more images of it on ...
1
vote
1answer
24 views

Why is power dissipated in a circuit maximum when external resistance is equal to the internal resistance in the circuit? [on hold]

[![question 24][1]][1]Suppose in a circuit the battery has emf 6V and internal resistance 3ohm. It is connected to an external resistance = R ohm. According to my ...
3
votes
1answer
45 views

Was the matter-energy content of our universe always distributed in the same ratios?

Currently, Dark energy (68.3%) and Dark matter (26.8%) together constitute about 95.1% total matter-energy content of the universe while only 4.9% is ordinary baryonic matter. Was this always the ...
1
vote
0answers
18 views

Wigner functions, symmetry

I'm trying to get more insight into quasiprobability distributions, as for example the Wigner function. There are some Wigner functions, which are symmetric. Symmetric: Fock state Thermal states ...
0
votes
1answer
39 views

Can this Temperature Scale be Considered an absolute temperature scale?

Me and My friend are having a discussion about Absolute Temperature Scales. I think Absolute Temperature Scales are those who have their zero on Absolute zero. So Can we define a new Scale (say ...
1
vote
1answer
33 views

What impact does water vapour have on incoming solar radiation?

About 55% of solar radiation at TOA (ie ~700 w/m^2 at peak) is in the infra red. This compares to about 530 w/m^2 at peak of terrestrial IR. Water vapour acts on this radiation, blocking and ...
0
votes
1answer
39 views

When were quarks discovered?

I know this sounds stupid. Especially to those of you who are actual physicists. I am a 7th grade above-level student who knows a little bit more that the basics of physics. I have recently discovered ...
5
votes
0answers
64 views

Bohr on wholeness?

I vaguely remember that it was Bohr who insisted that in a quantum experiment the whole experimental situation (but excluding the classical preparation and detection devices) must be considered as a ...
1
vote
1answer
27 views

boundary condition of electrical field

The boundary condition of electrical field is well known. $$ E^{\perp} _{above} -E^{\perp} _{below} = \frac{\sigma}{\epsilon_0}$$ Griffiths wrote that where there is no surface charge $E^{\perp}$ is ...
2
votes
0answers
28 views

Fermi's theory of beta decay - Does Fermi's Hamiltonian have the wrong transformation properties?

I'm studying the theory of beta decays as proposed by Fermi in the 30's, and I found an inconsistency between the transformation properties that he claims for his Hamiltonian and the transformation ...
1
vote
1answer
30 views

Help to solve a circuit with capacitor and resistor

Till now I'd never solved a circuit with resistor and capacitor. I'd seen the problem and tried to solve. But now I am in a doubt.The circuit was like that- My attempt-
1
vote
2answers
64 views

Shouldn't atoms of the same element repel each other?

Shouldn't the same type of atoms repel each other due to electrostatic charge?
3
votes
1answer
73 views

Is a type I Universe possible?

A type I universe (according to Max Tegmark) is a universe that is infinite and looks everywhere more or less like our universe does. Tegmark claims that within this infinity there are regions say ...
1
vote
0answers
18 views

What is frequency response of vibrating string? [duplicate]

If I transform wave equation for vibrating string Mx′′+Cx′+Kx=b(t) in linear system using $x_1(t)=x(t)$ and $x_2(t)=x_1^{'}(t)$ vibrating string equation becomes $Md_tx_2(t)+Cx_2(t)+Kx_1(t)=b(t)$. ...
1
vote
0answers
39 views

Why neutrinos are weakly interacting? [duplicate]

I recently attended a talk on neutrinos, where the speaker said there are billions of neutrinos passes through our body every second, but in our lifetime the probability of alteast one neutrino ...
5
votes
1answer
43 views

Why is reflected light polarised?

Why is reflected light polarised? I have learnt about Brewster's angle, and how at a particular angle all light reflected is polarised, but do not understand why. Is this something that could be ...
2
votes
0answers
22 views

Weyl semi metal vs entanglement entropy

In 2+1D, entanglement entropy (EE) is crucial for identifying a topological phase. What happens in 3+1d case? e.g. what are the behaviours of EE in WSM and trivial states?
2
votes
3answers
58 views

If I push my hands against each other, why does the stronger one move the weaker one if the forces should be equal and opposite [duplicate]

If I were pushing my hands against each other, the stronger arm will move the weaker arm, but if all forces have an equal and opposite reaction, why does the weaker one move?
2
votes
1answer
37 views

Self-energy of a Fermi liquid

A weakly correlated many-electron system can be viewed in a first approximation as a Fermi liquid, meaning that it behaves similarly to a non-interacting electron gas with renormalized parameters. In ...
1
vote
1answer
22 views

Why eyepiece does not resolve image formed by objective lens further?

In my book it is written that "The angular resolution of the telescope is determined by the objective of the telescope. The stars which are not resolved in the image produced by the objective cannot ...
-1
votes
2answers
93 views

What is my real weight? [duplicate]

My weighting machines notes my weight to be 65. Should I read it 65N or 65kg. PS: I only need a correct comment. This question is different, since, I know very clearly what mass and weight are. But ...
1
vote
1answer
66 views

Why does time always flow forward?

According to the BBC Earth " Physics says that any event in our day-to-day lives could happen in reverse, at any time".Then why can't we just turn time backwards?
1
vote
1answer
58 views

How does the Moon influence atmospheric pressure?

I have just read in the Telegraph an article entitled Moon overhead makes rainfall lighter, scientists conclude. In that article there is the following statement: When the moon is overhead, its ...
2
votes
4answers
64 views

Why is the Pythagorean Theorem used for error calculation? [duplicate]

They say that if $A = X \times Y$, with $X$ statistically independent of $Y$, then $$\frac{\Delta{A}}{A}=\sqrt{ \left(\frac{\Delta{X}}{X}\right)^2 + \left(\frac{\Delta{Y}}{Y}\right)^2 }$$ I can't ...
1
vote
0answers
23 views

1D Harmonic Oscillator: Eigenstate (|x=0>) at position x=0

Given an harmonic oscillator I need to calculate the eigenvector $|x=0\rangle$. Knowing that $$x|x=0\rangle = 0 \quad \Rightarrow \quad (a + a^\dagger) | x = 0 \rangle = 0 $$ I started to plug in the ...

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