# All Questions

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### What if proton is heavier than neutron? [closed]

What really happens to the atom if proton gets heavier than a neutron. I've heard that proton emits radiation. Plz explain
1 vote
18 views

### Is angular velocity about any point in a rigid body always the same?

Suppose I have a disc that is in translational as well as rotational motion. Doubt 1 If we talk about the angular velocity of the disc, about which point is this angular velocity measured? (I mean to ...
1 vote
32 views

### Question on special relativity

I am trying to learn special relativity. If we consider two inertial reference frames with spacetime co-ordinates $(t,x,y,z)$ and $(t',x',y',z')$ and let there be 2 observers who measure the speed of ...
18 views

### Convergence of rays at focal plane after reflection from concave mirror

My teacher taught us that rays parallel to each other(but not necessarily parallel to the principal axis), after reflection from a concave mirror,get converged at a sharp point somewhere on the focal ...
3 views

### Will the electrical potential difference between the Windward and Leeward sides of a mountain range generate electrical current?

I would like to know if its possible that the electrical potential difference between the Windward side and the Leeward side of a mountain range would be enough to generate a constant electric ...
228 views

### Wheel rolls hitting curb, how is the force of the curb on the wheel related to the initial velocity of the wheel?

To find the force for a wheel to scale a curb one must find where the force forwards produces a torque that is larger than that of the weight of the wheel but how can one relate this to the intitial ...
33 views

### Can the Strong CP problem be explained by the cancellation of quark electric dipoles by dipoles from some as yet undetected matter surrounding quarks?

I am not a mathematical physicist but from popular science articles I get the impression that CP violation occurs because quarks unexpectedly don't produce an electric dipole. If this is correct could ...
5 views

### Calculating temperature change out of a room

Currently I'm trying to find how the outside temperature affects the internal temperature of a room through its walls. I'm trying to use the convection heat transfer equation to find the exterior wall ...
35 views

### Can we catch signals from a cellphone using an external device? [closed]

What if someone stole em waves from our mobile devices to listen to our conversations or get our OTP. Whatever encryptions they have they are just EM waves innit and they cannot be propagated only in ...
78 views

### Looking for papers that claim that spacetime is emergent

This article states: It’s really striking that for most of the plausible theories of quantum gravity that we have, in some sense their message is, yeah, general relativistic spacetime isn’t in there ...
1 vote
522 views

### Finding the state space representation of a dynamic model with the force and angle as control inputs vector

I am trying to design a controller to control the angle of the force on my mobile rigid body. I some questions: I am not sure how to write the state space representation with the force, $F$ and angle,...
1 vote
128 views

### Vertical trajectory of a projectile with quadratic drag

I was wondering is there is an equation (or function) that can predict the apogee time and height of an object given its current acceleration and the usual constants ( mass, drag coefficient, cross ...
975 views

### Molecular origin of solid-liquid and solid-vapour surface tension

I understand that surface tension arises at the liquid-vapour interface due to the asymmetric nature of long-range attractive forces and the short-range repulsive forces acting on the interface where ...
64 views

### Gauge transformation rule for $dA$, where $A$ is the gauge field

Let $G$ be a non-Abelian simple compact gauge group and $\{ t^\alpha\}$ be a normalized set of generators for its Lie algebra $\mathfrak{g}$. Let $C^{\alpha \beta}_\gamma$ be the coupling constant for ...
39 views

### Entangled Photons passing different polarizers

Consider two entangled photons leaving a source. Both are polarized at angle 0. One travels to the left and the other to the right. The one on the left encounters a polarizer at 30 degrees and the one ...
109 views

### Doubt on conservation of angular momentum for Kepler's laws

Just before proving Kepler's laws, my Professor claimed that if $\vec{F}$ is a central force with center $O$ and it is the only force acting on a point $P$, then the trajectory of $P$ is a curve plane....
3k views

### Deriving Virasoro algebra question

I'm reading a book Lie groups, Lie algebras, cohomology and some applications in physics by Azcarraga and Izquierdo, and on page 347, when deriving the exact form of the central extension term I came ...
624 views

### Electric field inside current carrying conductor

Is the electric field inside current carrying conductor changing electric field or it is a constant electric field? And how this electric field produce magnetic field?
27 views

### Moving laser beam passing over stationary circular opening

I am in need of help with the following situation. I appreciate any insight. Imagine a circular laser beam of diameter d1 moving at velocity v passing over a stationary circular opening of diameter d2 ...
336 views

### What is the formal definition of Coupling efficiency

Does anyone knows the formal definition of Coupling efficiency? I have been reading the term in photonics devices and optics. I have been searching for it, but I could not find any. Thanks for the ...
156 views
+50

### Missing counterterms in $\phi^3$ + $\phi^4$ theory in 1PI effective action

I hope I'm just overlooking something. The Lagrangian is as follows: $$\mathcal{L}=\frac{1}{2}(\partial_\mu \phi)^2-(\frac{1}{2}m^2\phi^2+\frac{1}{3!}g\phi^3+\frac{1}{4!}\lambda\phi^4)$$ and I just ...
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9 views

### Doppler shift from a moving reflector and source if only the relative velocity is known?

Suppose there is a device which is producing and listening to sound (sonar), a reflector is moving with respect to device and the velocity of reflector and device with respect to the air is not known, ...
39 views

150 views

### Proper Time Along a Trajectory with Changing Velocity

I'm relatively new to SR and just encountered the Twin Paradox. I don't think I had trouble understanding the resolution to the paradox, but I was curious how an observer in an inertial reference ...
356 views

### Circular motion and banked roads question

I can't work out c) for the following question, and I'd just like some help clarifying why my solution is wrong. Part a) and b) are fine. A car rounds a bend on a road that follows the arc of a ...
54 views

### Have I correctly integrated Quantum Mechanics with General Relativity by involving the expectation value of the the energy-momentum tensor from QFT? [closed]

Have I correctly integrated Quantum Mechanics with General Relativity by involving the expectation value of the energy-momentum tensor from quantum field theory? Why the Energy-Momentum Tensor is a ...
33 views

### Dipole term in light-matter interaction

I have a question regarding the description of the term “dipole” in light-matter interactions. If I understand it correctly, there are 3 different things that one can declare as a dipole during light-...
23 views

1 vote
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### Energy output calculations for the very big heat exchanger

It recently emerged the concept of using deep wells as heat exchangers. It can be visualized as a long (2000 m) vertical tube with an inner diameter of 162 mm (the outer pipe diameter is 177.8 mm, ...
1 vote
60 views

### Why does a moon's orbit get more circular with time?

I understand that there is a transfer of energy between a moon and a planet depending on whether the moon is orbiting faster or slower than the spin rate of the planet. This would obviously change the ...
104 views

### Derivation of Schrödinger equation in Feynman-Hibbs

I am going through the derivation in chapter 4-1 of "Quantum Mechanics and Path Integrals. Emended Edition" by Feynman and Hibbs. The chapter starts with a proof of the equivalence of the ...