0
votes
0answers
15 views

Variable wavelength LED

Does there exist a type of LED (or other type of light source) that can change it's wavelength depending on the current/voltage it receives on a second wire? If not, would something like this even be ...
-1
votes
0answers
11 views

Numerical of capacitance [on hold]

what is the equivalent capacitance between A and B ?
0
votes
0answers
17 views

The difference between $R(r)$ vs $r$ graph for $4s$ and $5p$ orbital

Both orbitals have equal number of radial nodes (number of radial nodes = $n-l-1=3$). So the curve cuts the $x$-axis in 3 points. If it was $\psi^2$ vs $r$, then the curve would touch the $x$-axis at ...
1
vote
1answer
45 views

For infinitesimal Canonical Transformations, what functions are allowed for this to be a canonical transformation?

Consider two infinitesimal transformation: $$q_{i} \rightarrow Q_{i} =q_{i} + \alpha F_{i}(q,p) $$ $$p_{i} \rightarrow P_{i} = p_{i} + \alpha E_{i}(q,p) $$ where $α$ is considered to be ...
1
vote
0answers
21 views

Do we regularly measure and update our physical constants (By using the LHC)?

This question is motivated by sheer curiosity. I certainly do not expect that the free parameters we use in the standard model have changed in value since we started measuring them with a "modern" ...
0
votes
4answers
87 views

Can you tell your absolute speed in space?

Normally in relativity your speed can only be known relative to another object, given that as one approaches light speed more energy is required to accelerate faster, based on the energy consumption ...
0
votes
2answers
56 views

Can matter be formed from nothing?

Well, I wanted to know whether matter can be created from nothing? Could matter be created in pure vacuum or does it require some energy? If energy is required, How is energy converted to matter? If ...
21
votes
3answers
3k views

Are Hubble Telescope Images in true color?

Like many others, I have marveled at the images made available from the Hubble Space Telescope over the years. But, I have always had a curiosity about the color shown in these images. An example is ...
0
votes
2answers
36 views

If I touch an object, am I touching the atoms on its surface? [duplicate]

If I hit an object with a pen for example, does the pen touch the atoms on the surface of the object? Won't it damage the atoms? If I can't touch it, then where does the sound come from?
0
votes
0answers
22 views

Planetary alignment of the gas giants?

There is this nice and new applet of the orbits of the planets around the sun: Solar System Orrery You can click and drag any planet and watch their relative orbits evolve in time. I was curious ...
3
votes
1answer
69 views

Mechanism for visible light frequency mixing in storm clouds

So I know that when red and blue light (or the frequencies/wavelengths we percieve as such) hit our eyes with the correct proportions, our eyes and brains interpret that as the color purple. In ...
0
votes
1answer
59 views

With respect to what does time itself change? [duplicate]

We all have an intuitive notion that time itself "changes" - before it was the past, now it is the present, later it will be the future, and as time "changes" or moves forward what was the present ...
0
votes
0answers
22 views

Can a nozzle increase the thrust of a water rocket?

First of all, what is the correct equation to determine the thrust produced by a water rocket? $F_T = ṁ * V_e$ (1) $F_T = ṁ * V_e + (p_e - p_0)A_e$ (2) Using the first equation it should be ...
23
votes
6answers
4k views

Do all the conservation laws of Physics take no time to propagate?

For instance, conservation of momentum, does it take time to propagate between two or more objects? If it does, then there would be some moment that the momentum is not conserved. If it doesn't take ...
1
vote
1answer
28 views

Planetary Gravity and its effects [duplicate]

I live in Tunisia, exactly in Gafsa .. and there's a weird effect is happening, i really tried to ask people but no one had a clue, also i have seen that in other places on the internet. If you put a ...
0
votes
0answers
23 views

What's the best way to avoid slipping on ice? [migrated]

Where I live, winter is still a good bit away, but last year I slipped on ice and ended up with a black eye and a broken wrist. This year I sincerely want to reduce the chances of that recurring. I ...
-2
votes
1answer
52 views

Quantum Gravity [on hold]

By the Pauli exclusion principle fermions cannot occupy the same space, cannot have identical quantum numbers. The bosons however can. We also know that the universe, and in particular the various ...
0
votes
0answers
25 views

How much do we know about Quantum Gravity at energies larger than Planck energy?

What kind of predictions do current approaches to quantum gravity (superstrings/M-theory, loop quantum gravity,...) make at energies LARGER than Planck scale? Or is that a meaningless question? Does ...
1
vote
0answers
31 views

Why topological strings have to be closed or infinite?

Let's assume spontaneously broken global $U(1)$ group. During phase transition global topological strings are formed. Why they have to be infinite or closed (there doesn't exist finite strings)?
2
votes
0answers
32 views

Thomas precession, Lie algebra of the Lorentz group and the conservation of energy

If you read this post Thomas Precession, you will see a very good answer by WetSavannaAnimal, on the subject of Thomas Precession, which I am currently working my through, in conjunction with some ...
0
votes
3answers
53 views

Why is there no change in speed of a charged particle in a uniform perpendicular magnetic field?

When the initial velocity is perpendicular to the magnetic field, the force acting on the charged particle F = qvBsin(theta) ...
2
votes
1answer
29 views

Is circular masking a laser beam an acceptable way to get the beam diameter you require?

I am wondering what are the down sides to just masking a laser to get the beam diameter you require? For example if you have a collimated eliptical beam of say 2mm width and 4mm height, but you ...
0
votes
0answers
4 views

Blazed phase profile to generate laguerre gaussian beam

How to add blazed grating to a fork grating to achieve maximum diffraction efficiency in the first order while generating laguerre gaussian beam?
1
vote
0answers
63 views

In QFT do we always use normal-ordered Hamiltonian? [duplicate]

In quantization of the Dirac field I learned that we use normal ordering to get rid of negative energy vacuum state. From this point is there any reason we would use original Hamiltonian?
0
votes
0answers
15 views

Should i buy National Geographic Telescope NG 114 / 500mm DOBSONIAN [on hold]

I want to buy my first telescope. And want to go forNational Geographic Telescope NG 114 / 500mm DOBSONIAN.Is it a good telescope? What can i see with it? It has 114 mm. Aperture. It is coming for ...
1
vote
1answer
46 views

What is this form of mass conservation equation?

I found the following equation of conservation of mass (continuity) in "Computational Fluid Dynamics Vol.III" by Hoffmann: $$ \frac{\partial \rho}{\partial t} + \frac{\partial}{\partial x}(\rho u)+ ...
0
votes
2answers
53 views

Is a universal quantum computer expected to be able to shed any light on the measurement problem? - Part B

Following up on Part A. Suppose we build a universal quantum computer and it functions as we currently expect it to. Is there any reason to suggest that, beyond its uses for things like ...
0
votes
2answers
63 views

Time taken by a point in the light to cross the length of an object moving with a high velocity wrt to an observer at rest

I am new to the field of special theory of relativity and while understanding its concepts the following question popped into my mind... Suppose there is an object O moving with a very high velocity, ...
2
votes
0answers
68 views

Is a universal quantum computer expected to be able to shed any light on the measurement problem? - Part A

Suppose we build a universal quantum computer and it functions as we currently expect it to. Is there any reason to suggest that, beyond its uses for things like cryptography and quantum system ...
1
vote
1answer
33 views

What determines the melting point

I have read that the melting temperature of a metal depends on the distance between atoms: The idea behind the theory was the observation that the average amplitude of thermal vibrations ...
0
votes
1answer
46 views

How to understand tedious tension questions

A rope is wrapped $M$ whole turns round a cylindrical post, the two ends of the rope going in opposite directions. The coefficient of the friction between rope and post is 0.25. It is desired that ...
0
votes
2answers
33 views

Does the spring effect a moving ball? [on hold]

There is a ball attached to spring which is streched out. The ball is held by a machine on the ground so it does not move, but when it is released it will quickly contract. At the same time a ...
0
votes
0answers
43 views

Any applications of kinetic physics on cosmological scales?

On galaxy cluster scales, one is usually forced to use approximate theories such as hydrodynamics or magnetohydrodynamics for modelling cosmological phenomena. I wanted to ask if kinetic theory is ...
-2
votes
1answer
55 views

Why are these two angles the same? [on hold]

I can't find no similar or other relations between the two triangles, the two right triangles. However, if I look at it this way, the two triangles are indeed similar. But then this is a whole ...
0
votes
1answer
54 views

Is the formula, for finding the distance between two slits, my books gives correct?

In my book'a section on Young's double-slit experiment, the formula, $d = m \lambda \sin\theta$, is given. In this equation $d$ is the distance between two slits, $\lambda$ is the wavelength of light ...
1
vote
2answers
74 views

Is there a possibility of anti-dark matter?

Based on Galactic Gamma Ray Emission My question is simply put. Although dark matter itself is almost a complete mystery, has anything been published which postulates the existence of anti-dark ...
2
votes
1answer
82 views

Misconceptions about the universe - Hubble Sphere

I recently watched Veritasium's (excellent) video "Misconceptions about the Universe". However, he said something (at 2min 25s) which I think is wrong. Can somebody please clarify this one way or the ...
0
votes
1answer
55 views

Consistent method for finding direction of static friction

I am having trouble coming up with a consistent method of determining the direction of static friction. So far the best I have come up with is: it should oppose the relative acceleration the contact ...
1
vote
0answers
35 views

What's the name for the relativistic paradox with the train/car travelling over a gap?

There is a relativistic paradox I was introduced by a friend in Ithaca (Courtenay Footman). It involves a vehicle travelling over a ravine relativistically, so it's in the general family of ladder ...
0
votes
1answer
61 views

Asymmetry of relativistically treated EM force between atoms

There are two neutral atoms set separated at a long distance $R$ and let's consider them phenomenologically through Bohr model. Let's also assume that the nuclei (charged $+q$) of the atoms are fixed ...
1
vote
2answers
29 views

Why does the electric polarisation (polarisation density) have this direction?

It can be inferred that the amount polarisation $ P $ is dependent upon and proportional to the magnitude of the electric field $ E $ applied: \begin{equation} P \propto E. \end{equation} This ...
0
votes
0answers
15 views

Exact expression for the coefficient in Bloch-Grüneisen (BG) formula?

In most representations of the BG formula, there is a coefficient (usually left vague as an experimental parameter, but sometimes written out "analytically") in front of the integral: $$\rho=\rho_0 +A ...
1
vote
2answers
81 views

Modelling discrete spacetime

Supposed space and time were to be discrete, then how would i go about modelling this inside a computer simulation? In a simple 2D world, taking a square for example with side length $A$, then if ...
4
votes
1answer
95 views

How is classical information put into and retrieved from a quantum computer?

How, if you had to find the factors of say a 256 digit number, would you go about inputting the data and how do the proper answers "drop out" of a quantum computer. Other than terms such as qubits, ...
0
votes
1answer
79 views

Why we can't define energy in accelerating frame?

In my old unanswered question about accelerating frame, I have found (later after editing that question), that one of the keys is that energy is not defined in accelerating frame. What I do not ...
-3
votes
2answers
81 views

Why can't people just pump water from ground and flood deserts to make them habitable? [on hold]

I know this may be the wrong site, but I'm a curious man and I want to solve world's problems. One of big problems is deserts. They're so dry that nothing grows there. I was thinking about this and ...
0
votes
1answer
29 views

Finding the V(speed) of a 12KG bucket in pulley with the law of conversation of energy [on hold]

A system of two paint buckets connected by a lightweight rope is released from rest with 12kg bucket 2m above the ground floor. Use the principle of conservation of energy to find the speed with which ...
0
votes
0answers
25 views

What is the most energy efficient way to run an A/C unit?

I recently installed a 12,000 BTU Mini-Split A/C unit with an inverter - http://www.tempstar.com/products/dfac.html I was told that it uses approximately 0.6Kw/hour. What I am really curious about ...
1
vote
1answer
59 views

Canonical spinors from gauge transformations

In this 2006 paper, http://arxiv.org/abs/hep-th/0610128, there is the concept of gauge transformation and how was it employed that I do not fully understand. Note, what will be talked about below is ...

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