0
votes
0answers
3 views

Question about wave functions

What is meant by the "coherent wave function of a macroscopic body"? I found this phrase in a paper on QM, but am unfamiliar with the terminology.
0
votes
0answers
2 views

Why do metal surfaces reflect thermal signature?

I recently borrowed a thermal camera from a friend and I tried to observe my palm print over a reflective metallic plate. When I looked at it through the camera, it reflected my thermal signature too. ...
4
votes
4answers
924 views

Will gravity pull together two bodies from the other side of an empty universe?

Lets say that there are only two bodies in the universe, 65 kg each. Other than that the universe is completely empty, no neutrons, no photons, no dark energy/matter, not even neutrinos (that is to ...
2
votes
1answer
34 views

Operator product expansion in CFT

I'm on Polchinski's p39. Can someone please tell me the steps in the equivalence below? $$\exp\left[\frac{\alpha'}4\int d^2z_4 d^2z_5\ln|z_5-z_4|^2\frac{\delta}{\delta X^\mu(z_4,\bar ...
0
votes
0answers
6 views

How are heat transfer rate and heat capacity constant of a material related?

How are heat transfer rate and heat capacity of a given material is related? When I was a kid I imagined it like "Capacity is like a container or bucket of some sort, if it gets filled easily it can ...
-1
votes
0answers
5 views

Alignment of a triaxial accelerometer

I was wondering if someone could explain the alignment issues associated with a tri-axial accelerometer. It measures acceleration in terms of g. I have read some literature but I am unsure about the ...
2
votes
2answers
79 views

Does light bend in a vacuum?

I'm familiar with gravitational lensing but still I'm wondering if there is experiments (conducted here on Earth) which show that light bends due to gravity. For example mirrors setup to hold the ...
0
votes
3answers
47 views

What does raising voltage do?

If I raise the voltage of a wire from 0V to 1000V and then to 5000V, am I merely packing it with more and more electrons (with those electrons being trapped there until they find a path off the wire)? ...
4
votes
2answers
434 views

Which force is responsible for victory in tug of war?

I'm confused: In a tug of war game on rough ground who will win? The one who applies greater force on the rope or the one who applies greater force on ground?
-1
votes
0answers
12 views

Space Threading Theory alternate theory on time travel concept

The theory which makes the travelling to past looks feasible & possible in near future eliminating the paradox of killing of our own counterpart in past & change of future & establish ...
0
votes
2answers
47 views

How to model an apartment's airconditioning?

Background: This reminds situation reminds be of an episode from the The Big Bang Theory, although it is quite different from it. My roommate and I have similar temperature preferences and also share ...
1
vote
2answers
46 views

Inner products with orthonormal bases

Probably a stupid question here - I think it's a case of me not having sufficient mathematical background to follow this through. In Leonard Susskind's Theoretical Minimum book, he represents the ...
0
votes
1answer
62 views

Energy Stored in a Capacitor with and without Dielectric

I have seen the equation $V = \frac {V_0}{K}$, but also the equation $V=\frac{1}{2}CV^2$. The values of C and V increase in the same linear ration with K (because $C=KC_0$). However, as the energy ...
0
votes
0answers
10 views

Andreev reflection graphene - metallic superconductor

We have BdG equation, $$\left(\begin{array}{cc} \mathbf{p}\cdot\boldsymbol{\sigma} - V & \Delta_{0}e^{i\phi} \\ \Delta_{0}e^{-i\phi} & V - \mathbf{p}\cdot\boldsymbol{\sigma} \end{array} ...
26
votes
7answers
1k views

Are quantum effects significant in lens design?

Over on Photography, a question was asked as to why (camera) lenses are always cylindrical. Paraphrasing slightly, one of the answers and follow-up comments asserted that quantum effects are ...
6
votes
4answers
2k views

What happens to light in a perfect reflective sphere?

Let's say you have the ability to shine some light into a perfectly round sphere and the sphere's interior surface was perfectly smooth and reflective and there was no way for the light to escape. If ...
4
votes
2answers
128 views

Why is normal ordering a valid operation?

Why is normal ordering even a valid operation in the first place? I mean it can give us some nice results, but why can we do the ordering for the operators like that? Is its definition motivated by ...
4
votes
1answer
304 views

Why are magnetic field lines perpendicular to the surface of a ferromagnetic material?

It is known that magnetic field lines become nearly perpendicular to the surface of a ferromagnetic material. The quantitative proof which uses the boundary condition requires that magnetization at ...
0
votes
1answer
12 views

Calculating Resultant Force and Torque

I'm working on a sandbox game that allows the player to build a spacecraft and attach thrusters in arbitrary locations on the hull of the spacecraft. The game is set completely in 2D. (I'm a ...
1
vote
0answers
24 views

Superman physics

Spoiler alert for the animated film "Superman vs. The Elite": In the ending fight scene Superman flies off with one of the (more or less human) villains and when he comes back alone he answers to ...
0
votes
1answer
23 views

Weight held by jet stream of water

Consider a bucket of weight $W$, held in air by a jet stream of water from the ground (moving vertically upwards) at height $h$. The water is fired from the ground at the rate of $\mu$ (units ...
14
votes
4answers
1k views

Is one way glass possible?

I am not talking about mirrors, just a plain window made of glass like material. Would it be possible to allow light pass only in one direction but not the other?
2
votes
1answer
40 views

Electromagnetic field and continuous and differentiable vector fields

We have notions of derivative for a continuous and differentiable vector fields. The operations like curl,divergence etc. have well defined precise notions for these fields. We know electrostatic and ...
6
votes
3answers
822 views

Why is there a controversy on whether mass increases with speed?

Some people say that mass increases with speed, some people say that the mass of an object is independent of its speed. I understand how some (though not many) things in physics are a matter of ...
2
votes
0answers
14 views

Can expansion of space create energy?

In this question, expansion of space is considered, and it is explained that gravity and electomagnetic forces prevent matter from expanding. The idea I get in my head is something like a weight ...
0
votes
0answers
14 views

Coulomb Exhaustion

In thinking about a perturbation model for Coulomb's law, one could imagine photons spewing off of a charge in all directions. The chance of interaction with a near by charge being proportional to ...
5
votes
1answer
129 views

Force problem related to adhesive and bonding

I have two PCBs (printed circuit board), and they are glued by adhesives, as show in the pictures. And the location of the adhesives are indicated on the picture (please notice that NO adhesive is ...
0
votes
2answers
54 views

Why doesn't a car slide down a banked road when there is no friction?

In case of banked roads without friction, there is an additional $mg \sin(\theta)$ which is unbalanced. Why isn't this taken into account because it is responsible for making the vehicle slide down ...
11
votes
1answer
151 views

As the universe expands, the wavelengths of photons are stretched, and energy is lost. What about electrons?

Will electrons, and other particles, also loose energy as they travel through the cosmos? They have wavelengths. Do they get "stretched"? My guess is that the EM force, somehow, counteracts this ...
0
votes
1answer
30 views

Can we make a camera that fits in one of the bands of the double slit experiment?

So, in Young's double slit experiment, we see where the particle lands on the back wall. What if we were standing at the back wall, looking toward the slits? Could we gain more information not by ...
0
votes
2answers
253 views

Conversion of ideal gas to real gas via $Z$ compression factor

The ideal gas equation $PV=nRT$ can be converted into real gas equation by compression factor $Z$ i.e $PV=Z~ nRT)$. My question is what is $Z$ and how does it arise? Is $PV/nRT$ a compression ratio of ...
9
votes
5answers
600 views

How was the formula for kinetic energy found, and who found it?

My questions mostly concern the history of physics. Who found the formula for kinetic energy $E_k =\frac{1}{2}mv^{2}$ and how was this formula actually discovered? I've recently watched Leonard ...
0
votes
1answer
38 views

Magnetic field above center of current-carrying loop

A current $ I = 2A $ flows in a circular loop coil of radius $R = 10 cm$. Evaluate the magnitude of the magnetic field (in Tesla) at a point $P$ on the axis of the coil, and a distance $z=5cm$ away ...
0
votes
1answer
14 views

Can an experiment be designed to distinguish between actual wave interference and probability or pilot wave results?

I am a physics groupie, so please excuse me if this question is stupid, but I am trying to better understand the particle/wave duality in quantum physics. It would seem that, in the double slit ...
2
votes
3answers
44 views

What happens to a metal plate in the photoelectric effect?

In the photoelectric effect the electrons are supposed to be removed from the plate if light of appropriate wavelength hits the plate. If electrons are removed, the plate should get ionized ...
2
votes
1answer
41 views

What is the P-parity, T-parity and C-parity of graviton? Are these conserved in general curved space-time?

I'm curious about the P,T,C-parity of graviton? 1)Are these graviton's parities even or odd? 2)Is the C,P,T-parity alternatively conserved in Einstein gravity? And does the CPT theorem still hold ...
2
votes
1answer
144 views

Is work is equal to $mv^2$ (without $\frac{1}{2}$)?

I was trying to come up with an equation for work that doesn't include time, because I don't know time. Here's what I did: $$ work = Fd = mad = m{v\over t}d = m{v\over\left({d\over v}\right)}d = ...
3
votes
2answers
117 views

Is there any case of total transmission?

When light strikes the interface of two media some light is refracted and some is reflected. But, is there a case where no light is reflected i.e all the light gets passed through the given object. ...
1
vote
1answer
50 views

Brewster angle and perpendicular component

Fresnel's equations give that at Brewster's angle, the parallel component of the incident light is zero. The reflected perpendicular component is not zero, though. We can "remove" this component using ...
0
votes
0answers
15 views

Could non-locality imply a holographic universe?

I am just a physics groupie, so please excuse me if this is stupid. But wouldn't non-locality possibly imply a holographic universe? An analogy would be a projector and a hologram-- if a change occurs ...
0
votes
2answers
27 views

Restoring Force

Consider a pendulum hanging straight down. Say I pull it to the $\textbf{right}$ some angle $\phi$. Using Newton's laws in polar coordinates, I find that in the that force in the $\hat\phi$ direction ...
4
votes
3answers
245 views

magnetic scalar potential far above a magnetic film

The situation I am looking at is a magneto-static problem of a finite magnetic film with magnetization $\bf{M}$. I would like to find the the magnetic field far above the plate. My expectation is that ...
0
votes
1answer
27 views

Calculating deceleration from a non-constant force [on hold]

As a background : I am trying to design a spring to locate at the end of a zip-line (flying fox) to decelerate a person slowly. I am having some trouble working out the deceleration because it ...
1
vote
0answers
21 views

Is it possible to build a huge spaceship like the one of of Star Trek or Prometheus?

Ok, so theoretically, is it possible to build a spaceship like the ones we see off of Star Trek or Prometheus or will physics not allow it? What are some challenge faces such an task. Also, is there ...
0
votes
0answers
17 views

Tension on two string with one known angle and one known tension [on hold]

Consider a 50-N weight suspended by two wires as shown in the accompanying figure. If the magnitude of vector F1 is 35 N, find angle alpha and the magnitude of vector F2
1
vote
2answers
68 views

What is concept of temperture in ion trap?

As only several thousands of particles are holding in the ion trap, how can we understand the temperature?
1
vote
1answer
59 views

Physical/geometrical interpretaion of the determinant of a matrix

Consider a matrix transformation $\mathbf{T}$ that acts on a vector $\mathbf{x}$: $$ \mathbf{x}' = \mathbf{T}\mathbf{x} $$. Now, I know that one-dimensional linear transformations expand the length ...
0
votes
0answers
55 views

Lack of scale in Schrödinger equation for square-inverse potential

I see that if we set our potential in schrodinger equation to be a inverse-square dependence we don't have a typical unit of length as we have for hydrogen atom. $$-{\hbar^2\over 2m}\nabla^2\psi + ...
0
votes
1answer
18 views

Gravitational Potential Energy to Kinetic Energy

When a yo-yo is released from a height $h$, the gravitational potential energy is converted to kinetic energy. However, the yo-yo obviously has less acceleration than $g$, $9.8\frac{m}{s}$. This means ...
2
votes
2answers
145 views

Increased likelihood of photon emission due to “nearby” absorber?

Is an excited atom more likely to emit a photon if there is a similar atom in the ground state nearby ready to absorb it? When I say "nearby" I guess I mean that the absorber has an approximately ...

15 30 50 per page