2
votes
4answers
706 views

Detecting radiation from tritium keychain

I am measuring radiation from 6 tritium glow keychains. Usual gamma detector does not detect anything (this is expected), but on beta detector with thin window I am getting about 5 counts per second. ...
1
vote
1answer
74 views

Why does Se-82 undergo double beta decay?

Looking at the decay chain, I saw it undergoes double beta decay. How is it feasible for something to undergo a simultaneous double decay?
0
votes
1answer
82 views

How does time dilation work in this situation?

It is my understanding that when moving near the speed of light, time slows down relative to other things not moving so fast. Based on this principle, would it be theoretically possible to travel a ...
83
votes
5answers
22k views

Why would spacetime curvature cause gravity?

It is fine to say that for an object flying past a massive object, the spacetime is curved by the massive object, and so the object flying past follows the curved path of the geodesic, so it "appears" ...
1
vote
1answer
88 views

No-answers-found Li-Ion battery questions [closed]

Background Ive spent almost 7 hours researching about li-ion batteries because my Galaxy S2 only lasts 2 hours with all turned off and only 40 apps installed (removed system apps and bloatware) and ...
2
votes
1answer
1k views

Two ways of calculating the expectation value of momentum

The expectation value of momentum is given by: $$ \langle p\rangle = \int_{-\infty}^{\infty}\psi^{*}(x)\left(-i\hbar\frac{\partial}{\partial x}\right)\psi(x)dx $$ How can I show that the above ...
2
votes
1answer
160 views

Phonon scattering process in raman spectroscopy

I am trying to understand diagrams that involve showing phonon scattering processes that contribute to raman spectroscopy peaks. For example, I drew the one at the bottom of this post. This is ...
1
vote
1answer
79 views

Getting nonphysical results when solving for the index of refraction of a slab?

I'm trying to computationally find the refractive indices (real and imaginary) for a thin slab suspended in air (so the only indices to deal with are air and my material's). I've experimentally taken ...
0
votes
2answers
443 views

Two masses connected to a spring separated are charged to q Coulombs

I am working through Yale's Physics 201, and on the first problem set there is a question that is puzzling me. From my reasoning, I think the answer they provided is incorrect hence why I am here. The ...
1
vote
1answer
81 views

Increase thinking capability through relativity

As Einsteins relativity suggests that everything slows down along with the speed of light. So, if we were to live in space would our thinking capability (essentially speed) increase or decrease (due ...
6
votes
4answers
2k views

What is the current of a capacitor when the derivative of voltage is undefined?

This is from the textbook I am reading: I know this equation for capacitors: $$i=C\cdot \frac { dv }{ dt }$$ Here is my question: how can diagram (a) be allowed if the derivative of the voltage ...
5
votes
2answers
440 views

Can two media have same refractive indices?

Can two mediums placed under same conditions* ever have same refractive indices? *Pressure, temperature,etc.
4
votes
0answers
63 views

Why do floating objects attract? [duplicate]

Objects floating on the surface of calm water seem to be attracted to one another and tend to come together in a drift. Is this attraction like gravity?
3
votes
1answer
83 views

Mutually unbiased bases

This question can be formulated in two ways. Let there be two $d$-dimensional orthonormal bases $B_{1}$ and $B_{2}$. I refer to the elements of $B_{1}$ by $\lvert\nu_{i}\rangle$ and to the elements of ...
4
votes
1answer
175 views

Mirror Transportation

Why do people transport mirrors in inclined position? I frequently find people carrying mirrors in slant position on mini trucks.I guess it has some advantage of carrying them without breaking,and I ...
0
votes
0answers
144 views

Occupation probability in grand canonical ensemble

I have a system with energy spectrum which has two groups of $N$ degenerate levels (the gap between them is $E$). There are $N$ non-interacting fermions in the system. What is the occupation factor at ...
0
votes
0answers
75 views

Applied / environmental question: direction of exhaust fumes

I'm not sure the Physics StackExchange is the perfect place for this environmental/applied physics question, but as I found no forum more fitting I ask my question here. Otherwise please move my ...
0
votes
1answer
94 views

Group velocity of localized wavepacket

This is a Homework problem so please feel free to not answer and just give pointers. A localized wavepacket is given as: $$\Phi(r,t=0 ) = \frac { e^{-\large\frac {r^2}{2s^2}} e^{\large\frac{i\pi ...
3
votes
1answer
134 views

Isometries and Kaluza Klein theories

I am reading Bailin and Love's review on Kaluza Klein theories. On section 4.1 they start talking about infinitesimal isometries generated "with a particular generator $t_a$ of the isometry group". ...
0
votes
0answers
49 views

Why are there no true oneway mirrors? [duplicate]

"One way mirrors" are used in interrogation rooms etc. The wikipedia article states that: A true one way mirror does not, and cannot, exist. Light always passes exactly equally in both ...
2
votes
1answer
67 views

Having nano-scale holes in metal, possible today?

I am considering to design a gas filtering system that is based on the size of gas molecules. Basic idea is to flow mixed gas in a long pipe, and to allow CO2 to get of pipe through nano-size holes ...
2
votes
1answer
185 views

Relative Motion and orbiting planets [duplicate]

if all motion is relative to the frame of reference determined by an observer, why would the view that planet earth revolves around the Sun more correct than the view that the Sun revolved around ...
0
votes
1answer
317 views

Current vs Voltage Drive for Loudspeakers [closed]

Please see this article: here I don't know enough EMFT to comment on this but I am working on other tasks for a wireless speaker system prototype called "Busker's Friend". Completing my Schaum's ...
2
votes
2answers
396 views

Question about Majorana fermion and Majorana representation

In Chiral representation, a Majorana spinor looks like: $$\psi=\begin{pmatrix} \psi_L\\ -i\sigma^2\psi_L^*\end{pmatrix}$$ In this representation the Right handed field is the charge-conjugate of ...
0
votes
2answers
301 views

Air bubble inside glass

A convex glass lens acts as a converging lens when the medium around it is, say, air which is rarer than glass. But what happens if a "convex air lens" is inside a glass medium? Does it act like a ...
1
vote
0answers
321 views

Induced metric on the boundary of a manifold

The Gibbons-Hawking-York term which supplements the Einstein-Hilbert action is, $$S_{GH} = \frac{1}{8\pi G} \int_{\partial M} d^3 x\sqrt{-h} \, K$$ where $\partial M$ is the boundary of the manifold ...
1
vote
2answers
10k views

Is turquoise closer to blue or green?

I am having a discussion with my coworkers. Does anyone know what is the wavelength of turquoise color and whether it is closer to green or blue when comparing their wavelengths ?
0
votes
3answers
236 views

Turbofan: Efficiency wrt. the bypass ratio: “a lot of slow air > a little faster air”?

Reading / viewing up on how jet engines work, this video explains at the 9:02 mark that, for turbofan engines, ".. it is more aerodynamically efficient to have a lot of air moving relatively slowly ...
1
vote
2answers
521 views

Is preheating plates in microwave dangerous? If so, why?

My understanding of microwaves was that due to the high frequency they are easily absorbed into any material. The more "loose" the material, the easier the absorption. I know it's dangerous to let ...
0
votes
2answers
2k views

Schrödinger's Equation and its complex conjugate

I would like to know why there is a minus sign on the right-hand side of the Schrödinger's complex conjugate equation, whereas in the Schrödinger's equation there isn't. I know it is a simple ...
2
votes
7answers
587 views

Shouldn't the Uncertainty Principle be intuitively obvious, at least when talking about the position and momentum of an object?

Please forgive me if I'm wrong, as I have no formal physics training (apart from some in high school and personal reading), but there's something about Heisenberg's Uncertainty Principle that strikes ...
5
votes
0answers
419 views

Is non-relativistic quantum field theory equivalent with quantum mechanics?

Related post Can we "trivialize" the equivalence between canonical quantization of fields and second quantization of particles? Some books of many-body physics, e.g. A.L.Fetter and ...
0
votes
1answer
190 views

Do we stand on the earth because of Newton's third law?

This is the question I encountered and I'm not sure I understand. The Newton's third law say that, when a body 1 exerts a force on the body 2, then the body 2 will exert the same force on body 1, ...
1
vote
4answers
2k views

Why does diamond have lower tensile strength than Iron?

Let me first give you the tensile strength of both substance: Diamond: 16000 MPa Steel : 2617 MPa As you guys should know, tensile strength is how much a ...
1
vote
1answer
94 views

Why is $\left.\frac{\partial C_V}{\partial V}\right|_T$ different in these derivations?

I want to show that $\delta q$ is not an exact differential. Starting from $dE = \delta q - pdV$ and because $E := E(V, T)$ is a state function, which allows to express the exact differential as $$ ...
0
votes
2answers
198 views

How many equations are there to calculate distance?

I am an app developer and I am trying to build a physics app to calculate distance based on the quantities the user gives. for example if the user gives initial speed, time and acceleration, using ...
3
votes
2answers
956 views

Why is second moment of area often referred as moment of inertia?

In many references, mostly civil engineering, the second moment of area is referred as Moment of Inertia. Is that "really" correct? From my understanding, moment of inertia is analogous to mass in ...
1
vote
1answer
2k views

What is the relationship between Elasticity and Compliance?

Compliance is like elasticity of hollow tube. Elasticity is less for instance for arteries so they are less compliant. There seems to some sort of relationship between compliance and elasticity. ...
0
votes
1answer
62 views

Simple question about the tidal force (Leibniz's notation confuses me)

I started going through Taylor and Wheeler's Spacetime physics (standard textbook on special relativity). This is from exercise 2.8. Basically we're dropping a bearing ball from a 315 m height above ...
0
votes
1answer
254 views

Density as a function of Temperature?

I know that volume = mass/density....and density is the function of temperature. Is there any standard equation that describes density as a function of temperature? The system I am interested in is ...
2
votes
0answers
73 views

Solutions of PDEs in different coordinate systems

Suppose we have a PDE, for example the Helmholtz paraxial equation: $$ \nabla_\perp^2A+2ik\frac{\partial A}{\partial z}=0 $$ Solutions depend on the coordinate system we are using, i.e. we obtain ...
0
votes
1answer
441 views

Writing an arbitrary operator in bra-ket notation

An annoying fact about my physics textbook (Griffiths' Introduction to Quantum Mechanics) is that it introduces bra-ket notation without telling us how to use it. So I have a two-part question for SE: ...
0
votes
0answers
42 views

How to deduce equations 3.6.15 in Polchinski's string theory book? [duplicate]

In polchinski's first course on string, with how to deduce
1
vote
1answer
140 views

Refrigerator cooling power usage

I have a refrigerator, that makes a lot of noise, and we have therefore set a time on it will limit the run time to when we are not at the office. But this is where our discussion begins, should we ...
2
votes
1answer
231 views

Microcanonical Ensemble

I'm having difficulty understanding a statistical mechanics problem. I'm missing some basic understanding of counting the minimum energy states. My thought is that there are three states to choose ...
8
votes
1answer
792 views

Why quantising gravity necessarily give us gravitons?

Gravitons are supposed to be the quanta of gravitational field My question is, if we do not know how to quantize gravity yet, how do we know that quantizing it in principle should give us gravitons, ...
1
vote
2answers
89 views

Quarks are now considered to be fundamentals, but so were atoms some time ago. So the way we see is only limited by our technological advances? [duplicate]

After watching this FuseSchool - Global Education episode, I cannot stop thinking how can something not have a substructure, how it cannot be split? http://www.youtube.com/watch?v=nlv06lSAC7c
0
votes
1answer
153 views

Airfoil theory — Why does air travel faster above? [duplicate]

I do not understand, why the air above the airfoil travels faster than the air below it? The air above has to travel faster than the air below so that both streams meet simultaneously at the ...
2
votes
1answer
480 views

Stress energy tensor and the covariant derivative of the 4-momentum

Another basic question. I have usually seen the stress energy tensor $T^{ij}$ described as the flow of the 4-momentum field $p^i$ along direction $x^j$ in spacetime with $p^0$ as energy and $x^0$ as ...
3
votes
1answer
196 views

Is it possible that the universe in its entirety is discrete rather than continuous? [duplicate]

Since electric charge is comprised of discrete units and and mass is formed by discrete units is it possible that space-time itself is discrete as well?

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