3
votes
0answers
48 views

What is the idea behind counting the number of excited states and the representation of a group ?

While reading Polchinski's Chapter 1, I encountered the following on page 24, "For example, the $(D-1)$ dimensional vector representation of $SO(D-1)$ breaks up into an invariant and a $(D-2)$-vector ...
2
votes
2answers
52 views

Can the magnetic fields of EM radiation be harnessed or measured?

We use the electric component of EM radiation to create the EM radiation and to detect it (antennas and Etc.), but does anyone know of a situation where the magnetic component of EM radiation is used? ...
3
votes
0answers
29 views

Active-sterile mixing for KeVins

People sometimes talk about KeV mass sterile neutrinos as a warm dark matter candidate. I think they call them KeVins (horrible name btw). Now, In order for it to be a good dark matter candidate it ...
1
vote
1answer
65 views

parity invariance of Einstein, Maxwell and Dirac Lagrangians

How can we show that Einstein, Maxwell and Dirac Lagrangians are parity invariant?
0
votes
1answer
36 views

Will an electron gun fire behind it?

If an electron travels as a wave, can it therefore not be aimed with any precision? If you fire an electron gun, can't you aim it at a particular slit? If the electron travels as a wave, will an ...
0
votes
2answers
54 views

Can a hydrogen atom sit still?

Can we take a single lone hydrogen atom (proton and electron?) and set it in one place and observe it staying there? How about just a proton? A neutron? How about just an electron?
0
votes
2answers
38 views

Deriving spring oscilation period [duplicate]

We have a spring attached to a wall and at the other part an object on a frictionless surface. I tried to calculate the spring oscilation period. I used the conservation of energy and kinematics ...
0
votes
1answer
13 views

Effect of crystal growth on its scintillation

How does crystal growth affect its scintillation properties? What are possible ways in which growth of CaWO crystals grown via Chochralski method could be modified to avoid non-linearity in its ...
1
vote
1answer
28 views

Historical analysis of light interference - difference frequencies

It is well-known that light of two different frequencies illuminating a detector will produce an output with a component at the difference frequency. While such considerations are eminently useful ...
-1
votes
0answers
34 views

Lack Of Definitions?

I am reading French and Taylor's Quantum Physics textbook, and I am having some difficulty parsing a few words. One such word is the gram-equivalent. The author's seem to never explicitly define ...
0
votes
1answer
32 views

Which function denotes the energy of thermal motion within a system?

In thermodynamics, the heat $Q$ is defined as a type of energy in transfer, and is not a state function, which function denotes the energy of thermal motion within a system? 1) $TS$, (there is a ...
-1
votes
0answers
23 views

heat supplied by two heat source in reversible heat engine [on hold]

A reversible engine is supplied with heat from two reservoirs at 900 K and 600 K and rejects heat to a sink at 300 K. The engine develops work equivalent to 90kJ/s and rejects heat at the rate of 56 ...
3
votes
0answers
37 views

Berry's phase: in which space does the degeneracy appear?

This question follows a previous one of mine: Adiabatic theorem and Berry phase. In his original paper [ M. V. Berry, Proc. R. Soc. Lond. A. Math. Phys. Sci. 392, 45 (1984) ], Berry discussed the ...
0
votes
1answer
20 views

measuring pressure drop of air flow over a pipe [on hold]

I am working on a project like fluid flow analysis(air flow), i have tried to calculated the pressure drop over the flow using u tube manometer , the pressure head ( the difference in manometer ) is ...
0
votes
0answers
17 views

Any help available for Solid State Electronic Devices and Materials? [migrated]

I am teaching and doing research work in Solid State Electronic Devices and Materials, which is a subset of Materials Science & Engineering - a branch of Applied Physics. I want to know if this ...
2
votes
1answer
34 views

In a radioactive Bose-Einstein condensate, would all the atoms disintegrate simultaneously?

They're all supposed to do the same thing - so I suppose they would? Also, would the resulting half-life be the same as that of the individual atoms it is made up of?
2
votes
1answer
32 views

How to calculate the drag coefficient using terminal velocity?

I was wondering if it were possible to calculate the drag coefficient by allowing an object to reach terminal velocity. Can you rearrange the terminal velocity formula to give the drag coefficient?
0
votes
1answer
38 views

Kinetic energy and potential energy variation over distance in SHM

When you compute the average potential energy of a horizontal spring mass system from the mean position to the positive amplitude A, the value comes out to be $\frac{1}{6}kA^2$. For the average ...
1
vote
0answers
26 views

What is it that makes an electron maintain a distance from the positively charged nucleus? [duplicate]

What is it that makes an electron maintain a distance from the positively charged nucleus? Why aren't electrons merely pulled into and absorbed by the nucleus ?
2
votes
3answers
132 views

Describing a circular current loop as delta functions

It would be really nice to see how Jackson got eqn 5.33 on his example problem for finding the vector potential of a circular current loop $$ ...
3
votes
3answers
77 views

In scattering, how does a particle 'know' which direction it is being illuminated from?

In scattering experiments, for example light scattering, the scattering strength from different sized particles is depicted as below. What I can't understand is: how does a particle know which ...
1
vote
1answer
57 views

Distance and velocity question

I know that speed is the derivative of distance. So integrating speed should give you distance. Let's suppose we have a speed which obeys this function: $$ v(x) = 2^{2^x} $$ So at time 0 the speed ...
3
votes
2answers
96 views

How “unnatural” is the universe? [on hold]

Looking to read up on the impact the discovery of Higgs boson has on the String Theory I came upon these two paragraphs in an article about the Higgs boson Nobel Prize: One possibility has been ...
14
votes
4answers
3k views

How did they take photos of Jupiter?

How did they take photos of Jupiter - I mean Jupiter is illuminated and that's a lot of light to produce. Am I missing something, and there was some sort of dark photo technology used, or was there ...
3
votes
2answers
80 views

Cartesian Coordinates to Polar Coordinates

I apologize if this question is trivial, but I am new to physics and am struggling with some of the basic concepts. Working in $\mathbb{R}^2$ with standard coordinates $(x,y)$, suppose we have a ...
2
votes
1answer
68 views

Killing Equation, trouble with tensor algebra

I'm attempting to follow a proof that the commutator of two Killing vectors is itself a Killing vector. The source that I've posted is from my course notes. I've highlighted the part I'm stuck on. ...
1
vote
1answer
37 views

Woodwind instruments overtones [duplicate]

When playing woodwind instruments, e.g., flute, if one blows harder, the sound will be one octave higher. Even harder gives even higher overtones. Does anyone know why?
2
votes
1answer
40 views

Where will a board break when weight is added to the end?

If you have a board, say a standard 2x4 of finite length, where one end is fixed in a cement wall and the other end is free, and you begin adding weight to the free end until it breaks, where will the ...
4
votes
2answers
139 views

Variation in measurements of $g$ on the Earth's surface due to the Moon's gravity

A book, Exercises for the Feynman Lectures on Physics, has recently been published. It consists of homework problems to provide practice with the techniques and concepts used in the famous Feynman ...
2
votes
3answers
43 views

Intuitive explaination for why higher engine compression ratio is more efficient?

Intuitively to me it seems likes increasing compression ratio would require more work to compress the gasses before ignition, so you'd just end up getting back what you put in - like a spring. What am ...
1
vote
3answers
50 views

Double rainbows

In my garden, when I'm watering the plants I sometimes see a rainbow or two. How did two rainbows appear? Why can't I see three rainbows then, or how can I see three rainbows?
0
votes
0answers
12 views

How to detect if a beverage has Sucralose or aspartame? [migrated]

There is a drink that claims to be sweetened with stevia, but I think I taste Sucralose in there even though it is not listed on the ingredients. Is there any easy way I could test for the presence ...
0
votes
2answers
69 views

The Alcubierre drive and closed timelike curves

Under what conditions would it be possible to create closed timelike curves, assuming an Alcubierre drive could exist? Would it be possible to have the latter without the former? See here for ...
0
votes
1answer
36 views

How to show that the gravitational potential energy of a two particle system is -2 times the total kinetic energy, without using the virial theorem?

Consider a two-particle system with identical masses, orbiting in circles about their center of mass. I'm supposed to prove that: $$U_p = -2U_k$$ With $U_p$ potential energy of the system, and $U_k$ ...
0
votes
3answers
53 views

Is duplication of nucleus, electron and proton (sub-atomic particles) possible? [on hold]

usually a single cell develops into a huge mass to form a substance or an organism. is this happening because of multiplication of sub-atomic particles? if yes, then is it possible to multiply the ...
3
votes
0answers
46 views

Free charge movement in an electric field - including bremsstrahlung

Let us imagine a free, negatively charged object that is in rest and placed in an elecric field of a point positive charge. The positive charge has a huge mass and cannot move, so we consider only the ...
0
votes
0answers
23 views

Help With Wakefield Integrals With Implicit Variables [on hold]

My calculus is really rusty (damn Mathematica/Matlab) and I was wondering if anyone could help me with an equation I am having trouble integrating. I have attached a snapshot of the paper I am trying ...
1
vote
0answers
46 views

Higher-Dimensional Metrics in (Hyper)-Spherical Coordinates

I want to compute the components of the Riemann curvature tensor (for a case similar to the Schwarzschild solution) in 4 + 1 dimensions, but I want to use a higher-dimensional analogue of spherical ...
2
votes
1answer
36 views

Fringe Pattern Brightness for Young's Double-slit experiment

Perhaps I have missed something in my notes, but I have noticed when looking at different sources that some textbooks/sites state that the fringe brightness for the young's experiment is the same for ...
2
votes
2answers
74 views

What is the performance of a silicon crystal that makes it an essential component to computing

I'm on a thread of interest in the precise physics that allow the creation of the computing process. It began as a question posted in search of an understandable explanation of what physical form ...
0
votes
1answer
52 views

How does an accelerating charge radiate electromagnetic waves? [duplicate]

When a charged particle gets accelerated it emits electromagnetic waves. In reality, when a charged particle gets accelerated the electric field around the charge remains unchanged, but the magnetic ...
1
vote
0answers
28 views

Can the rate of virtual pair production from vacuum be computed?

Consider for instance the QED Lagrangian. Is it possible to compute the rate of virtual electron-positron creation from the vacuum?
14
votes
2answers
956 views

Why there does not exist any Gravitational Magnetic Field?

We think that the electric field and gravitational field operate similarly with their corresponding charges/masses. With just a difference that the electric field is sometimes attractive and sometimes ...
0
votes
2answers
36 views

Charge Distribution in Reissner-Nordström Black Holes

In an electrically charged black hole, such as the one described by the Reissner-Nordström metric (i.e. with no angular momentum), where would the electric charge be situated (neglecting any charged ...
0
votes
1answer
32 views

Quantum mechanical proof of Conway's SPIN and TWIN axioms?

I think I understand correlations of EPR-state and GHZ-state which deal with spin-1/2 particles and (-1, 1) measured values. Conway's state is spin-1 particle state with (-1, 0, 1) measured values. ...
0
votes
0answers
11 views

Hullo! Why can't people with reputation less than 20 post in the chat session? [migrated]

Your reputation mark is not the criteria for defining who is better at physics and who is not.. Even people with less reputation than 20 can have much interest in Physics and may have questions that ...
2
votes
1answer
40 views

Why do my ice cubes stick together?

When I put ice cubes in a glass of water, I find that sometimes they will stick together and form a sort of "bridge" between them as they melt. There is usually a visible line where one ends and the ...
-1
votes
2answers
47 views

Find electric field given the magnetic field [duplicate]

Given the magnetic field as a vector, how do I find the electric field?
-4
votes
1answer
26 views

Does gravity related to dark matter? [on hold]

How is it possible that a Plajaren beamships could fly through space without any interaction with it which makes it possible to travel with the speed of light or even higher than that?
3
votes
5answers
1k views

Why aren't units with powers, like cm³, surrounded by parentheses?

Since $\renewcommand{\unit}[1]{\,\mathrm{#1}} 1\unit{dm} = 10^{-1}\unit{m}$, it follows that $1\unit{dm^3} = 10^{-1} \times 10^{-1} \times 10^{-1} \unit{m^3} = 10^{-3} \unit{m^3}$. However, in ...

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