4
votes
1answer
270 views

What does it mean to “wrap” a D-brane around some manifold?

I am getting quite confused with this terminology when I read the papers. Like while constructing the near horizon $AdS_3$ in the $D1-D5$ system one considers $IIB$ on $R^{1,4}\times M^4 \times S^1$ ...
6
votes
3answers
2k views

What happens if I throw a battery into water?

Today I have by accident thrown a AAA battery into a bucket of water. I fished it out of the water immediately (within 20 seconds or so) and nothing notable had happened and the battery is still full ...
0
votes
1answer
65 views

How does this particle behave in the magnetic field?

I have the above question and I have though about it every way and can't seem to find out. So what I have concluded (ignore the answers on the img) Is that the force is on the z axis because the ...
0
votes
0answers
65 views

Imagine a 50-mile tower spanning from desert floor to the Karman Line

CORRECTION: The structure weighs 1.568E15 kg.s Does the structure effect the equilibrium of earth's rotation? Would momentum from Earth's rotation apply lateral force to the structure? What else do ...
0
votes
1answer
104 views

What happens if a body free-falls at a certain speed?

It is known that a body falling to the ground is affected by gravity, and its velocity increases by 9.8 m/s per second. But when this body is falling, and it reaches the speed of 340 m/s (the speed of ...
12
votes
2answers
298 views

The formal solution of the Schrodinger equation

Let's have Schrodinger equation (or some equation in Schrodinger form) $$ \tag 1 i \partial_{0} \Psi ~=~ \hat{H} \Psi . $$ One likes to write that it has formal solution $$ \tag 2 \Psi (t) ~=~ ...
0
votes
1answer
75 views

Failure of a simple stat mech simulation

so I did a simple simulation that I thought would yield a Boltzmann distribution, but it failed to, and I was wondering if anyone has insight into why it failed. Ok, so I had a simple discrete system ...
0
votes
0answers
43 views

Rolling resistance

Today, my physics teacher asked the following question (and gave it as homework): How can a moving body deaccelerate both in means of center of mass and rotationally? I quickly answered that ...
1
vote
1answer
209 views

Meaning of heat sink in engine analysis [closed]

I am confused with the meaning of sink. What part of vehicle engine acts as reservoir and what does as sink?
-1
votes
1answer
182 views

Can we have a static point in the universe? [closed]

Big bang theory states that the universe began from a single point (which we may consider as a central frame of reference for the objects in the Universe). In 1929, Edwin Hubble confirmed that the ...
1
vote
1answer
128 views

Does the light speed change in media? [duplicate]

Does the light speed change? The Theory of Relativity says that the speed of light in vacuum is the same and unchangeable, while I read that the speed of light in glass is lower than in air, and that ...
1
vote
1answer
121 views

The self-coupling constant for the Higgs mechanism

I have a few questions about the parameter $\lambda$ in the Higgs-Lagrangian density $$\mathcal{L}_H=(D_\mu \phi)^\dagger D_\mu \phi + \mu^2\phi^\dagger\phi-\lambda(\phi^\dagger\phi)^2$$ Is it ...
1
vote
1answer
275 views

How is the current flow perpendicular to the wire?

This answer gives a great explanation of how surface charge builds up to force the current to move perpendicular to the wire: http://physics.stackexchange.com/a/102936/41086 However, it fails to ...
1
vote
0answers
47 views

“Forgetting” the initial condition in conservative oscillations; What has been “forgotten” exactly?

I am training myself on oscillations. The topic is self-sustained oscillations. The claim is these oscillations are NOT forgetful about their initial condition as opposed to conservative oscillators ...
1
vote
6answers
1k views

How does one exert greater force on the ground by jumping?

When one jumps, how does he/she manage to exert greater force on their ground than their weight? Also, what is normal force and the reaction force (are they the same thing?) and by newton's third ...
0
votes
1answer
90 views

Comparing unknown temperature scales [closed]

Source: Principles of Physics by Resnick, Halliday, Walker. $9^{th}$ edition. Chapter 18. Problem 6. On a linear $X$ temperature scale, water freezes at $-125.0^0X$ and boils at $360.0^0X$. On a ...
0
votes
2answers
50 views

What would be the minimal size of an aerial vehicle capable of sustained suspersonic flight? [closed]

I wonder, what's the smallest possible size for a UAV capable of sustained supersonic flight at the current technology level? Let's say 10 minutes of flight at 1.1 M.
6
votes
3answers
549 views

What is the commutator of an operator and its derivative?

Is it possible to calculate in a general way the commutator of an operator $O$ which depends on some variable $x$ and the derivative of this $O$ with respect to $x$? $${O}={O}(x)\\ ...
-3
votes
1answer
56 views

Query on Polarization [closed]

Describe the state of polarization represented by (here w = omega and TT = pi) a) $E_x = E\sin(kz - \omega t)\,\& \,E_y = E\cos(kz - \omega t)$ b) $E_x = E\cos(kz - \omega t) \,\&\, E_y = ...
1
vote
0answers
29 views

Superconducting loop as a particle detector?

Imagine that one has induced a persistent current in a superconducting loop. If a particle interacted with an electron in one of the Cooper pairs then would some decoherence and dissipation occur? I ...
2
votes
0answers
132 views

Definition of a non-pertubative Quantum field theory

How do you define a non-perturbative Quantum field theory. What does it mean? I was just digging around some math about the meaning of $Z_1$, and such in terms of probabilities. It turns out these and ...
1
vote
1answer
134 views

Stress-Energy Tensor

As of recent, I've been doing a bit of self education in GR, equipped with a working knowledge of the key elements of the differential geometry in GR, and in looking at the Einstein-Rosen bridge, I ...
1
vote
0answers
142 views

The Maxwell and the Boltzmann distributions

I am trying to understand where the Boltzmann distribution comes from. I recently learned some interesting things of which my interpretation follows below. Did I interpret correctly? If so, is this ...
2
votes
1answer
189 views

Red color has largest wavelenght and violet minimum (in the range of visible light). then why does violet light appears reddish? RED + BLUE = VIOLET [duplicate]

My question is simple. Green light is more similar to red light than violet, then why is violet reddish and green not? in the language of frequencies and wavelengths, red and violet should contrast ...
43
votes
5answers
9k views

Why does a candle blow out when we blow on it? Our breath is 16% oxygen and only 4% CO2

Don't say that a layer of carbon dioxide covers the flame, because our breath has more oxygen than carbon dioxide. Also, our breath does not cool the flame as it is itself warm. So what is happening ...
1
vote
0answers
132 views

Drift velocity of electrons in a superconducting loop

Do electrons travel at the Fermi velocity in a superconducting loop? For metals the Fermi velocity seems to be around $10^6$ m/s. So would electrons (in a Cooper pair) travel around the loop at this ...
0
votes
0answers
32 views

Aim of the Michelson Morley Experimetn [duplicate]

What was the aim of the MM experiment? Many sources say that it was to measure the relativity velocity of the Earth through the aether. But I'm trying to understand what this exactly means, and why ...
2
votes
2answers
111 views

Order of magnitude estimation for some intriguing questions

The physics TA showed us a few examples in which one can estimate many things from first principles, sound logic, and scaling arguments. This led usually to understanding of why some numbers have the ...
2
votes
0answers
49 views

Casimir Invariants of the Galilean group

I had studied a couple of things about Galilean and Poincare group. But in the Galilean group, there is not enough clarity on how to calculate generators for boosts ($B_i$), which if I do it seems I ...
6
votes
1answer
120 views

Doubts about the ideal gas law

EDITED AND SOLUTION: In fact my stupid mistake was to take the wrong value for my $P_1$ and I was getting an 1.2998 that finally is a 1,9178 within just a difference about 7%. So at the end they are ...
1
vote
0answers
59 views

Dispersion in a rectangular prism

Why are the colours visible only at the fringes of the light refracted through a rectangular prism?
0
votes
0answers
20 views

Clarification about “projections and correlations” in Heller's Quantum Gravity

The footnote (bottom) for the following paragraph from “Creative Tension: Essays On Science & Religion” by Michael Heller, has “such a projection, being always “onto,” switches off all possible ...
4
votes
1answer
103 views

Question on static electricity & electron transfer

Static electricity is caused by the transfer of electrons between substances right? For example, take a balloon and your hair. Both are stable and electrically neutral. So why would electrons jump ...
1
vote
2answers
104 views

Visualising scalar and vector fields

As I have been studying electromagnetic theory, I have always been lead to confusion when trying to visualise the fields. Fortunately, the electric and magnetic fields are vector fields and also along ...
1
vote
0answers
35 views

antimatter moving back in time [duplicate]

This just blew my mind away! I was watching a video about imagining the fourth dimension and the narrator said that little line. Can some people elaborate on this. Also please keep it simple not ...
-1
votes
2answers
233 views

capacitor in ac and dc circuits

In a dc circuit work done by battery=QV while energy stored in capacitor =(QV)/2 loss in energy=(QV)/2 While a capacitor in ac circuit has a no power loss.why is it so? Shouldn't heat be lost in ac ...
1
vote
3answers
607 views

What makes water heavier than air?

I apologize in advance if this is too basic for this site. Considering that hydrogen is lighter then oxygen, and water is 2/3 hydrogen, and only 1/3 oxygen, and our "air" is comprised mainly of ...
0
votes
1answer
189 views

Correlation Between Hz and KWH (power consumption)

Is there a direct, or even exponential relationship between the amount of Hz and power consumed in KWH? In other words, take this example: Let's say a power company changes it's regulated output to ...
5
votes
1answer
231 views

Are they the same thing: Wigner distribution in quantum Boltzmann equation and Wigner function in quantum optics?

We know that quantum Boltzmann equation (QBE) is an equation of motion for the interacting Green's function $G^<(\vec{x}_1,t_1;\vec{x}_2,t_2)\equiv\mathrm{i}\langle ...
0
votes
0answers
110 views

Calculate trajectory of projectile with gravity from disk planets in 2D?

I'm making a 2D game where you control a spaceship and fly between disk-formed planets of differing size (mass/pull). The planets are small and you can fly near several at once. I need to calculate ...
0
votes
1answer
23 views

Inhomogeneties in gravitational acceleration at the surface of the Earth.

I am looking for data sets which clock the time and precise location of free falling bodies in a vacuum. I have been told that the acceleration of gravity is not absolutely 100% uniform, and I would ...
4
votes
2answers
242 views

Acer saccharum (Sugar Maple) Sap & Freezing

This may or may not be the appropriate scientific discipline to ask this question of, but I'll give it a shot. I'll happily invite chemists to chime in as well. It's time to tap sugar maples in the ...
0
votes
0answers
22 views

How does band narrowing (heavily doping the emitter) affect the alpha F and alpha R in the Ebers-Moll model of a BJT?

I think that when the emitter is heavily doped, the bandgap is reduced which increases the reference forward current(current flowing through the E-B junction ) but the alphas themselves do not change. ...
1
vote
1answer
75 views

Measurements for thermal diffusivity of graphene?

We have known for a long time that graphene has in-plane thermal conductivity ranging between 2000 and 4000 $W m^{-1} K^{-1}$. But in order to model heat transport on a sheet of graphene, we need more ...
5
votes
2answers
227 views

what determines the wavelength of waves on the open ocean?

Looking at the picture below, you can totally see that these are tiny boats. The water is practically washing over the hull of these boat models. But the water has boundaries that are very far ...
2
votes
0answers
29 views

Difference between positron and electron scattering in Coulomb field

In first order of perturbation theory the S-matrix amplitude for electron scattering in the Coulomb field will be (up to normalization factors) $$ S_{fi} = \frac{iZ q^2}{\sqrt{2E_{f}2E_{i}}}\bar ...
1
vote
3answers
42 views

What are the means to consider that a specific function is phase of an oscillator?

I hope the experts of the field forgive me for this n00b questions, but I am just trying to understand physics. Assume the following function: $$\phi(t)=\omega t+\cos(\omega t)$$ The above function ...
6
votes
2answers
157 views

A question to clarify the use of divergent series in calculating the casimir effect

Some time ago I posted a question here on this forum. I would like to ask some questions regarding the way the energy per unit area between metallic plates is calculated. The full calculation is on ...
2
votes
2answers
177 views

If energy is just a conserved quantity how can it have flux and density?

As I'm very well convinced for now, the better understanding of energy we have today in Physics is that of a conserved quantity, i.e, a numerical valued associated with a system that remains the same ...
2
votes
2answers
216 views

How can I tell that circular motion is a solution for a particle confined to the surface of a cone?

I'm working on a problem where a particle of mass $m$ is confined to the surface of an inverted half cone (and is circling downwards due to gravity), with the cone's half angle $\alpha$. I chose to ...

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