# All Questions

40 views

### Expectation value of an operator and commutator relation

I have a quantum operator $A.$ It's expectation value is constant respect to time. I mean $$\langle \psi(t)|A|\psi(t)\rangle$$ is a constant values. If I know $|\psi(t)\rangle$ is not an eigenstate ...
57 views

### Are there different types of photons?

What are the differences and likenesses between Laser and Magnetic Photons? What are other types photons?
27 views

### Given the 1st Postulate of SR, doesn't the 2nd Postulate go without saying? [duplicate]

i've been looking over possible duplicates of this question and haven't found one yet. so, using Wikipedia as the textual source: The Principle of Relativity – The laws by which the states of ...
21 views

### why will two bodies rotate about their centre of mass if they do so for their mutual attraction

If two bodies rotated because of their mutual attraction. They will do so about their centre of mass. Why is that ? I understand that if there is no external force then the centre of mass must not be ...
22 views

### Shape of an inverse cube orbit?

If I have a particle orbiting a central force $$F=-k/r^3$$ what is the shape of the orbit (the radius as a function of the angle)?
39 views

### Quantum mechanics and Second law of thermodynamics

Recently I came across this idea of Gibbs that, it is the coarse-grained entropy that always increases, whereas the fine-grained remains a constant. So classically, coarse graining refuses us some ...
28 views

### Divergence of inverse square and the dirac delta

Alright, so I know: $$\nabla\cdot \frac{\hat{\bf r}}{r^2} = 4\pi\delta^3 ({\bf r})$$ however I'm having difficulties showing that $$\nabla\cdot \frac{\hat{\bf R}}{R^2} = 4\pi\delta^3 ({\bf R})$$ ...
12 views

### Compton effect in photo-electric?

In photo-electric effect Einstein said that photons incidents on material and gives their energy which will gives kinetic energy to electrons. But i also want to know that why Compton's effect not ...
20 views

### Do a receiving antenna interfers with an emitting antenna?

As I understand: Accelerating electrons generate electromagnetic waves. An emitting antenna have an alternating current (electrons are moving) which generates an electromagnetic waves. The ...
20 views

### I m just try to make Free energy using buoyancy [duplicate]

Can I make power (electricity ) using buoyancy see diagram. if this diagram is possible then how much power i get . I just need formula for upwards speed.
18 views

### How to deal with boundary conditions for path integrals?

For non-relativistic quantum mechanics, the boundary conditions are rather simple to deal with, they are just \langle x_1, t_1 \vert x_2, t_2\rangle = \int_{x_1(t_1)}^{x_2(t_2)} ...
58 views

### What does “charge” actually mean? [duplicate]

I know that a charged particle is defined as a particle that experiences a force in an electric field, as explained in this post: What does a subatomic charge actually mean? However, I still don't ...
16 views

### What are physical observables that are connected to orbital angular momentum?

We considered a system that is confined to a curved surface. In the quantization process, we have obtained an additional orbital angular momentum that are from the surface geometrical deformation. Now ...
8 views

6 views

### Discrepancy of capture from 2p+1 state to 2p(+-1)

In the (nlm) characterization of hydrogenic orbitals. Consider the collisions H+ + H(2p+1) ---> H(2p-1) + H+ H+ + H(2p+1) ---> H(2p+1) + H+ where an electron capture has ocurred. Should the ...
29 views

### Possible inconsistency in Bohr atom model

It is well known that Bohr model is not totally right. But I recently discovered a very curious inconsistency (if I am right) which I haven't seen explained anywhere. The first postulate of Bohr ...
28 views

### A drop falling in the condensed air

A drop is falling in humid air with air resistance equal $F_r = - \alpha v^2$. In $t = 0$ the drop is ideally spherical, $h$ above the ground, has mass $m_0$ and velocity $v_0 = 0$. What mass and ...
20 views

### Filling a charged capacitor with dielectric material

If there is a charged capacitor (capictance $C$) connected to a battery (of EMF $V$) and the space between the plates of the capacitor is filled with a dielectric material (dielectric constant is ...
15 views

### Is there a way to make a heat pipe that can transfer heat downward?

Is there a way to make a heat pipe that can transfer heat downward? As in a 10 to 20 ft vertical pipe with 100°f at the top and 50°f at the bottom.
20 views

### When Sugar Is Added to Water, How Does the Mass Change, and How does That Affect the Water's Density and Boiling Point?

I can't find a good answer anywhere. How does the amount of sugar added change the boiling point, mass, and density of water? Does it affect the mass or the volume? Or both?
23 views

### Age difference between hands and feet due to relativity?

According to relativity time passes faster the faster something moves, and gravity slows time. My head is moving faster than my feet (assuming I'm not at one of the poles). My head is further away ...
19 views

### Given magnetic field, calculate electric field

The B field depends on z and t so that $B = j B_{0}cos(kz-\omega t)$ where k is the wavenumber, $\omega$ is angular frequency and $B_{0}$ is constant. The electric field is \$E = E_{x}i + E_{y}j ...
21 views

### Tension at different points of a string during vertical circular motion

For a vertical circular motion, its standard to solve for tension at the 4 common points on the circle (North, South, East, West) My question is: Is it possible to solve for tension at other ...
30 views

### Why aren't pictures of Pluto darker than those of other planets?

Just as the intensity of the light from a candle decreases with distance, I would expect the light from the sun to illuminate the distant planets less than the closer ones. However, the pictures of ...
55 views

### Are there continuous spacetime events?

What is the formal definition of an event? According to Wikipedia, "an event is a point in spacetime (that is, a specific place and time) and the physical situation or occurrence associated with it." ...
29 views

### Non-zero gravitational anomaly

Analogous to the Adler-Jackiw-Bell anomaly of QCD, we have an anomaly in gravity when we consider gravity to be coupled to chiral fermions: \partial_\nu J^\nu_5\propto R\tilde{R}, ...
14 views

### Why can't gamma rays penetrate through the atmosphere? [duplicate]

I recently read a book which said that the gamma rays can't penetrate through the atmosphere. Why?
16 views

### Pressure,Pascals Law

Lets say that i have 2 different types of containers, one cuboidal and another one conical. and lets say both these are massless and fully contain water. **1.**In the cuboidal one the pressure ...
26 views

### How would you define δQ (heat) in terms of changes in Volume only? [on hold]

Background: I have a problem (in biology) on which I was brooding for many moons. Currently I'm thinking about solving it with a help of building an isomorphism between economy and thermodynamics. ...
9 views

### Diffraction grating with film covering half of slits

If I have a film covering part of my slit of finite width is it justified to take the integral of the wave elements with there phase difference as a function of x across each half separately ...
14 views

### Application of centroid of body in real life

What is the practical application of centroid of the body whose centeroid lies out of it. I know that we can balance a body at its centroid but what if lies out of that body?

15 30 50 per page