# All Questions

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### Electric field 2 half lines [on hold]

The 2 semi lines split on O by angle phi constant, each line have charge density landa , i want to calculate E (M) where OM=x this is not homework , im self studying well i tried the following ...
21 views

### Help to find a simple setup for optical surface topography

I'm looking for some help from someone expert in optics to create an inteferometry based setup to map the surface of a small object. This is for a small lab project so I'm not looking for a really ...
24 views

### Speed of AC and DC current

If AC current oscillates as it passes through a conductor is it slower than DC current which does not oscillates?
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### The effect of 8 hours 20 degrees C sunshine on the temperature of a stationary car's engine block? [on hold]

What temperature of the engine block could be achieved by parking a car (Mazda 3) in full sunlight and facing south all day. Average day temperature 20 degrees Celsius no wind. And then how long to ...
50 views

### Looking for a specific theory concerning Dark Matter [on hold]

I am looking for the name of a theory positing that "empty" space itself is not empty, but has substance, and that "fabric" or "substance" is actually what we call Dark Matter. In theory, dark matter ...
33 views

### Why superconductor have vortex

Sorry guys I really don't understand the idea of vortex in superconductor, why superconductors type II have vortices ? Thanks in advance!
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### What does a long half-life imply? [on hold]

If an element has a long half-life then, what can we say about the rate at which it decays? Thank you.
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### Does the current in a resistor depend on the speed of electrons?

If the speed of electrons in resistor is slow, then will the current be slow and if the speed of electrons is fast, then will the current be fast? Does the current in a resistor depend on the speed of ...
66 views

### Inserting the resolution of identity correctly

In a text on path integrals, I find the following: \langle q_{j+1}|e^{-i(\hat{p}/2m)\delta t}|q_j\rangle = \int\frac{dp}{2\pi}\langle q_{j+1}|e^{-i(\hat{p}/2m)\delta ...
32 views

### Difference between mechanical modes and phonons

As stated in this review article: Mechanical modes are long compared to the interatomic spacing. It is natural to make the distinction between nanomechanical modes and phonons: The former are ...
42 views

### In which experiments the charge to mass ratio of proton was determined?

Are there experiments where the charge to mass ratio for protons have been determined in the same way as in Thompson’s experiments (where he determined the charge to mass ratio of electron) but with ...
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### References on particle cooling

I am looking for references on the topic of particle and mechanical oscillators cooling, in particular: Doppler cooling Resolved sideband cooling and Lamb-Dicke regime Stokes and anti-stokes modes ...
29 views

### Is negative energy(work) less than positive energy(work)?

We cannot talk about magnitudes in case of work, but if someone did (-42 J of work) by stopping a moving object. And if someone did 42 J of work, by pushing something, who did more work? Does it ...
35 views

### What happens when a contracted object going at speeds comparable to light is fit in a tight space, but has been brought to rest

What happens when a rod of length L moving at a speed comparable to the speed of light, is made to fit in a space of length say 3/4*L and is brought to rest. Does it exert some force on the walls ...
27 views

### Regarding law of conservation of energy

what will happen in a vacuum when an object is dropped in moving van(completely closed) and when same object is dropped outside the moving van? what will be its final position in both the cases in ...
18 views

### Does frame dragging apply to linear motion?

Firstly I will admit I do not understand the cause of rotational frame dragging. https://en.m.wikipedia.org/wiki/Frame-dragging In order to better understand the mechanism, I would like to know if ...
16 views

### Why is the energy lost due to the internal resistance always equal to $(1/2)CV^{2}$ in a simple capacitor battery circuit? [duplicate]

Suppose we have simple circuit in which a battery of EMF $E$ is connected to a capacitor of capacitance $C$. Work done by battery $W_{b}=CV\times V$ and energy stored in capacitor ...
76 views

### Modern explanation of the Young experiment with Quantum Field Theory?

In the Young double slit experiment it is possible to detect the arrival of individual photons as well as an interference pattern. It doesn't makes much sense to me that something could be either a ...
128 views

### Is the reaction force for a stone hitting a wall infinite?

Let us assume a rigid stone which moves in empty space with a constant speed of $v$. (Or in the air with no friction and drag or you can imagine a free fall with friction). This stone hits a rigid ...
29 views

### Difference between DMRG(density matrix renomalization group) and MPS(matrix product states)?

I am learning DMRG recently. I noticed there are many papers both in the DMRG approach and MPS(such as variational matrix product state(VMPS) by F.Verstraete and J.I.Cirac) approach. In my eyes, there ...
22 views

### How to calculate turning acceleration from a compass? [on hold]

I have degree and timestamp and want to calculate the turning acceleration. I what to trigger some code when the compass is turning fast. Is there a mathematic way to get an turning acceleration ...
33 views

### Motion of parallel-incoming particles in gravitational field [on hold]

There is a large parallel beam of incoming particles with mass $m$ and uniform velocity $v_0$ ($v_0 \ll c)$ in the presence of a gravitational field of a (spherical) planet with mass $M$ and radius ...
24 views

### anatomy of combustion

I don't understand how energy is released in combustion. We have a reaction of a combustible material with oxygen and this releases energy. In what form is this energy released? It should be some ...
21 views

### Force on a charged particle due to an uncharged infinite conducting plate

How can I calculate the force on a charged particle due to an uncharged infinite conducting plate? If there is a small object with positive charge placed above a metal plate, the object induces a ...
20 views

### Why does emf of a cell equal to $\frac{F_b d}{q}\;?$

In Concepts of Physics by H.C.Verma, it is written: Some internal mechanism exerts forces on the charges of the battery material. ... We show the force on a positive charge $q$ as $\vec F_b\; .$ ...