# All Questions

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### How sodium atoms in lamp are energized to produce light?

In a recent spectroscopy lab I performed for one of my classes we used a Lambda Scientific LLE-1/2 mercury/sodium lamp (to look at the sodium doublet) and a Lambda Scientific LLE-8 hydrogen/deuterium ...
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### Metric of following spacetime and refractive index

Let's have metrics $$ds^{2} = f(\mathbf r)dt^{2} - h(\mathbf r )\delta_{ij}dx^{i}dx^{j}.$$ Hot to show that motion of light in spacetime with this metrics is equal to motion in continuous media with ...
254 views

### Holes in a P-type semiconductor under external force E

Basically in almost every semiconductor texts, there will be all these concepts concerning electrons, holes, dopants, fermi-levels. However, I have been always confused about the picture of hole ...
335 views

### Massless spin 1/2 particle

Could a massless spin 1/2 particle, or more generally massless half-integer spin particles exist? Does it make sense to say that they could be described for example by the Dirac equation by forgetting ...
152 views

### Negative energy solutions Dirac equation without radation field

In the book "Relativistic Quantum Mechanics" by Bjorken and Drell in Chapter 5.1 page 64 there is the following statement about the problem of negative solutions to the Dirac equation: By their ...
54 views

### When viewed from a telescope, does an object get more magnified if its angular diameter is increased?

and if yes, how can the diameter be increased? Lets say I want to view saturn from a small telescope. Increasing the angular diameter will give a better magnification if the answer to the above ...
85 views

### Why is th $\hat{r}$ component zero in this integral?

I'm trying to evaluate the magnetic field by calculating the Coloumb integral $\overrightarrow{A}$, and later I will take: $$\overrightarrow{B}=\nabla \times \overrightarrow{A}$$ However, in the ...
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### What spin-statistics is a magnetic monopole expected to obey?

What statistics (or spin) is a magnetic monopole expected to have? Does it depend on the theory used?
70 views

### how does graphene affect the refractive index of an optical waveguide?

Could someone help me find data on the electro conductivity of graphene and its effect on the refractive index of an optical waveguide
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### Does photons undergo the process of cyclic absorption and re-emission by virtual particles in vacuum?

The process of cyclic absorption and re-emission by electrons in a medium is an explanation for the fact that light appears to slow down in mediums relative to vacuum. But, does light undergo this ...
291 views

### Feynman diagrams for interacting theory of scalar field

Is it correct that the number of lines originating from vertices on Feynman diagrams is equal to the order of phi in interaction lagrangian for scalar field?
706 views

### Period of small oscillations [duplicate]

A light elastic string is stretched between two points, one lying vertically below the other. A particle is attached to the mid-point of the string, causing it to sink a distance h. Assuming that ...
230 views

### Do any other particles get excited(or absorb energy) by photons like electrons?

Electrons get excited to different energy levels when photons of specific frequencies fall on them.But, is there other particles which absorb the energy of the photons?
373 views

### Value of of gravity 9.8m/sec^2 and centrifugal force [closed]

I had a doubt regarding centrifugal force on earth is not accounted in any equations as object falling towards earth.eg f=ma.i read questions asked by few about the same and got to a conclusion that ...
79 views

### Which number should I suppose to $a$ (width of well) and $m$ (mass of particle) in potential well problem? [closed]

I tried to plot a complete of state functions of potential well problem but graph was so weird. I thought a cause was variables a and ...
421 views

### Why is Planck mass much larger than the smallest mass that we actually know about?

The three fundamental constants $h$, $c$ and $G$ are manipulated and rearranged in different ways to get the Planck time, Planck mass etc. The Planck time is said to be the smallest time possible and ...
922 views

### Why is the speed of light considered as a fundamental constant if its speed changes with medium resulting in refraction? [duplicate]

I know that the speed of light, the universal constant of gravitation and the Planck's constant are considered to be the three fundamental constants of the universe. But, why is speed of light ...
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### Are background independence and diffeomorphism invariance the same?

What is the difference between background independence, which loop quantum gravity formalism claims to have, and diffeomorphism invariance?
371 views

### Do electromagnetic fields interact with air pressure?

I would like to know whether electric and magnetic fields interact with air pressure. Do changes in magnitude or direction of such fields increase or decrease the air pressure in a given volume of ...
51 views

### Reversed freezing point

Helium-3's Phase diagram shows that at the right temperature and pressure combination, the solid region dips downward as temperature increases. That means that you can heat it up and it will freeze. ...
1k views

### Motivation for form of Lagrangian

This question (in lagrangian mechanics) might be silly, but why is the Lagrangian L defined as: $L = T - V$? I understand that the total mechanical energy of an isolated system is conserved, and that ...
64 views

### How Long is this Projectile in the Air? [closed]

A projectile is launched a horizontal distance of 200 meters, at an angle of 45 degrees. Launch and impact heights are the same. How long is the projectile in the air? I think the initial ...
278 views

### Paramagnetism and large N

In a paramagnetic system, we have: $$N = N_\uparrow + N_\downarrow$$. If we have a large system, with $N >> 1$, is it generally okay to assume $N_\uparrow \approx \frac{N}{2}$ and ...
65 views

### Determining the limits of an integral

In Griffiths' Introduction to Electrodynamics, Problem 1.28 (the triangular prism question) is especially challenging for me. I do not know how the limits of x are 0 to (1-y). My concern is the ...
5k views

### If I lift a box vertically, why is the work I do equal to the distance I lift it times the force of gravity on the box? [duplicate]

I have problems fully understanding the concept of work, so please forgive me if this is simple. If I take a box of mass $m$, and lift it a distance $d$ vertically, why is the work I have done ...
226 views

### Is the relative atomic mass directly proportional to the size of an atom? [closed]

I have a piece of homework, i have to make a pair of models depicting pure metals and alloys. I want it to be as accurate as possible, and so i'm asking this: Is the relative atomic mass directly ...
71 views

### tracking a satellite

The following article says that because the GOCE satellite has a polar orbit, it is impossible to track where it will land. "The satellite is one of the few satellites in a Polar Orbit. ...
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### How much extra distance to a CERN event horizon? [duplicate]

How much extra distance would a scientist have to travel to get to the event horizon of a mini black hole if they ever make one?