5
votes
2answers
112 views

If you lift something does the internal energy increase or remain unchanged?

So change in internal energy $\Delta U = q + w$; so in lifting an object you do work on it, thus increasing its internal energy. Is this correct? Sorry if this is a stupid question.
1
vote
2answers
150 views

electrostatics and magnetism

Let a square loop be placed in a uniform electric field in a position of stable equilibrium. Then, because of the electric field, if the electric field is in the rightward direction then a positive ...
5
votes
2answers
375 views

Viscous Burgers equation physical meaning

The viscous Burgers' equation: $$ q_{t}+q\:q_{x}~=~\nu\:q_{xx}, \mbox{ where } \:\:\nu >0, $$ combines the nonlinear propagation of $q(x,t)$ and the diffusion. What is this equation for? (in ...
4
votes
2answers
729 views

What causes Potassium to decay into Argon the way it does

From evolutionwiki: "Potassium 40 decays into argon 40 through a process known as electron capture. In electron capture, an electron from the innermost electron shell "falls" into the nucleus, ...
0
votes
0answers
22 views

Measuring a capacitor accurately

I want to accurately measure the value of an electrolytic capacitor at DC voltages, and accurately predict its voltage based on current drawn from it, or put the other way, accurately measure the ...
0
votes
0answers
45 views

Functional Differetiation of a complex functional

Suppose I have a simple functional $$F=\int{dx\;\phi^{*}(x)\phi(x)}\tag{1}.$$ Assuming $\phi(x)$ and $\phi^{*}(x)$ are independent and I take a functional differential with respect to $\phi(x)$ and $\...
1
vote
2answers
166 views

Otto and Carnot efficiency comparison

Lets say both engines operate between same temperature limits. Carnot eff: $$ e_\text{Carnot} = 1-\frac{T(L)}{T(H)} $$ Otto eff: $$ e_\text{Otto} = 1-\frac{T(4)-T(1)}{T(3)-T(2)} $$ ...
0
votes
1answer
107 views

Boomerang angular momentum

So I'm building a boomerang to fly 200 feet in order to do that I was told to increase the moment of inertia to increase the resistance from change in state, and I was told that it would increase the ...
-3
votes
0answers
38 views

Twin paradox without gravity

Suppose we have 3 people Person1 was already born on a spaceship that travels in the speed of 0.5c toward person2 Person2 was born in a point in point in the space also in the exact time of person1 ...
0
votes
2answers
56 views

Free fall vs throw with air resistance

If I let a stone drop from a certain height and throw a stone from a certain height, with air resistance, which will reach the ground first? When I draw a free body diagram the air resistance in the ...
11
votes
1answer
233 views

Significance of the exception to Gleason's Theorem when n = 2

Gleason's Theorem famously asserts that (appropriately defined) measures on the lattice of a complex Hilbert space can be implemented by density operators via the trace operation, except in the case ...
1
vote
1answer
36 views

Vacuum persistance amplitude

E. Fradkin's Field Theories in Condensed Matter Physics formulas 3.57 and 3.58: I feel really sad about it, but all my tries of getting from formula $$ Z = \operatorname{tr} \hat{T} \prod_{j=1}^{...
4
votes
3answers
433 views

Distinguishable, Indistinguishable Paramagnetic Ideal Gas

In the canonical ensemble, the partition function for an ideal gas is given by: $$\frac{Z}{N!}$$ The factor $N!$ accounts for the indistinguishability of the particles of the ideal gas. What ...
2
votes
1answer
41 views

Clarifications on Ampere's Law

I have just learnt Ampere's Law, useful for calculating the magnetic field in situations having a high degree of symmetry. However, I have some conceptual doubts regarding it: Before I begin, I would ...
0
votes
0answers
9 views

What can be the result of interaction of H- ion (2.1 MeV) and stationary H2+ ion?

I believe there is Coulomb scattering. However, are there any other channels? Could the products of the reaction be H and H2, and what would be the cross section of this reaction?
0
votes
0answers
11 views

Projectile on inclined plane [on hold]

Two inclined planes OA and OB as shown . A particle is projected from point P with velocity u along a direction perpendicular to plane OA . If the particle strikes plane OB perpendicularly at Q , ...
7
votes
5answers
2k views

Measuring the speed of light and defining the metre - absolute or relative?

If the metre is now defined as the distance light travels in vacuum in 1⁄299,792,458th of a second and the speed of light is accepted to be ...
3
votes
2answers
45 views

Could a pocket universe be birthed out of the negative pressure in our universe?

I have just recently started learning about inflationary cosmology so I don't know much about it. But from my understanding, the theory says the big bang was started by the expansion of a small region ...
3
votes
2answers
914 views
+50

What's the relationship between weakly hypercharged bosons and Higgs bosons?

In this video, Leonard Susskind does a good job trying to explain succinctly the Higgs field and exactly how it gives elementary fermions mass, except for one point he seems to skip a few things. The ...
-1
votes
0answers
41 views

Intuition behind deriving the FRW metric

Consider a 3D sphere embedded in a 4D “hyperspace”: $$(x^1)^2 + (x^2)^2 + (x^3)^2 + (x^4)^2 = a^2,\tag{74}$$ where $a$ is the radius of the 3D sphere. The distance between two points in 4D space ...
0
votes
1answer
104 views

1-D Fick's first law - partial derivative?

I've recently been reviewing some concepts, including diffusion. Fick's 1st law: $$J = -D\frac{\partial C(x,t)}{\partial x}$$ as I understand it, applies to the steady state. For 1-D diffusion and ...
0
votes
0answers
22 views

Is mass relative? [duplicate]

This question has to do with the relativistic mass of an object. I have been reading that as energy increases, so does mass to a much lesser extent, and that this applies to kinetic energy as well. ...
0
votes
0answers
4 views

Liquid metallurgy [on hold]

I want to know more about liquid metallurgy? all i know it is a technique used for fabrication of material. Please help me if you know about this technique. Thank you.
0
votes
0answers
26 views

How is a irreversible process (conventionally) represented on a $T-S$ plane and why cannot it be (really) represented?

A reversible process can be represented on a $T-S$ plane, and the area under the curve is the heat exchanged by the system. On $P-V$ plane a irreversible process is conventionally represented with a ...
0
votes
0answers
63 views

Lorentz transformation: Can distance between two observers depend on the observers? [on hold]

Consider reference frames S and S'. S' is moving in positive x direction at speed v relative to S. Time measured by S is t and that measured by S' is t'. When t = 0, then t'= 0. Coordinate systems ...
2
votes
1answer
70 views

Proof of two Lorentz-algebra identities

I am currently working through the QFT introduction text by Peskin and Schroeder and try to fill in two identities that I wasn't able to prove (it should be fairly simple, but my experience with this ...
0
votes
1answer
19 views

Charge density on two hemispheres, enclosing a conducting sphere [on hold]

Two uniformly charged non conducting hemispherical shells each having uniform charge density $\sigma$ and radius $R$ form a complete sphere (not stuck together) and surround a concentric spherical ...
59
votes
5answers
6k views

If dark matter only interacts with gravity, why doesn't it all clump together in a single point?

I'm a complete layperson. As I understand, dark matter theoretically only interacts with the gravitational force, and doesn't interact with the other three fundamental forces: weak nuclear force, ...
1
vote
1answer
399 views

Force of a solenoid on a ferromagnetic material

As I was trying to find an answer to another problem, I was informed that the equation I was using would not work. The equation I was using was $$F = (NI)^2\mu_0\frac{\text{Area}}{2g^2}$$ If this ...
4
votes
3answers
221 views

Are there Gauge fields that are not 4-vectors?

In my understanding Gauge fields are fields that have some kind of redundancy, i.e. a transformation that does not change the physical state. As far as I can see all the Gauge fields in the Standard ...
-4
votes
2answers
41 views

How to resolve “bottleneck” of encoding input of quantum computer? [on hold]

As far as I understand, all quantum computing purpose is to accelerate exponentially (upon input length) computation time of given task. But here user faces bottleneck to serialize input, and ...
0
votes
1answer
27 views

Electric Field of Bar [on hold]

Problem: Positive charge $+Q$ is distributed uniformly along the positive $x$ axis from $x = 0$ to $x = a$. Negative charge $-Q$ is distributed along the $-x$ axis from $x = 0$ to $x = -a$. A point ...
0
votes
0answers
6 views

Charpy problem, Impact velocity [on hold]

Calculate the velocity of the hammer of an impact testing device at its lowest position if the hammer starts moving at an angle 30° to the horizontal (mass of rod=0.5kg, length of rod 400mm. mass of ...
0
votes
0answers
8 views

I can't get the right solution to this thermal expansion problem [on hold]

The problem : A glass flask is filled to 'the mark' with 60 cm3 of mercury at 20 ºC. If the flask and its contents are heated to 40 C ºhow much mercury will be above the mark? $\alpha$ for glass : 9....
4
votes
1answer
246 views

Closed timelike curves in the spin-2 gravity formalism

Let's say we take some topologically trivial CTC spacetime, like the Gödel metric: $$ds^2 = -dt^2 - 2e^{\sqrt{2}\Omega y} dt dx - \frac{1}{2}e^{\sqrt{2}\Omega y} dx^2 + dy^2 + dz^2$$ And then I ...
0
votes
0answers
16 views

Physics problem: stage of rocket [on hold]

A manned rocket is rising with a velocity of 3 km/s. At exactly 2000m, it disconnects the first rocket stage. How long does it take the stage to hit the ground, and what is the velocity of impact.(...
0
votes
0answers
18 views

Conditions to find standing waves harmonics

I came up with a doubt on standing waves conditions. The type of question I find difficult to answer is of the following type. Consider a rope. I do not know if the rope is fixed at both end or at ...
9
votes
8answers
320 views
+50

How to pour water from a bottle as fast as possible

When one pours water out of a bottle, it first flows smoothly but then a pressure 'blockage' develops and the pouring becomes interrupted and turbulent, so that the water comes out in splashes. This ...
0
votes
3answers
52 views

Tension in a string with pulley and two objects at opposite ends

Tension is confusing me. According to my understanding of tension the tension in a string is uniform but while going through the solution of a problem I read that tge tension on the left part of the ...
1
vote
2answers
15k views

Would a light or a heavy ball roll fastest down a slope?

A small, light ball and a larger, heavier ball are released from the top of a slope. Which will move further? which will come down faster?
1
vote
1answer
48 views

Can we derive Biot Savart law from Coulomb's law?

Can we derive Biot Savart law from Coulomb's law by setting a current source at an instant in place of one of the charges? Let's say $dl$ is the length of the conductor having $dQ$ charge which ...
0
votes
1answer
69 views

Point charge inside a electrically neutral cavity in conductor placed eccentrically, and effect of external electric field if switched on

bear with me, but i would like a definite answer, now, starting off the external charge density on the outer surface of sphere WILL be uniform by unique solution of Laplace equation and letting the ...
0
votes
1answer
228 views

Why does amplitude of a mechanical wave increase and then decrease with increasing driving frequency?

I was doing an experiment where I explore how the frequency of the oscillation of a vibrating water hose (the end of the water hose), affects the amplitude created by the water path (a wave-like ...
-4
votes
0answers
29 views

how to work out the probability of walking through a wall [on hold]

I was in science on Friday and I asked my teacher how to calculate the probability of walking through a wall.I just was curious because I like learning quantum mechanics
0
votes
1answer
23 views

Energy loss of photons crossing a dielectric medium

How much energy do photons lose when crossing an "isotropic" dielectric medium? What would be possible mechanisms. I assume the straight forward answer would be that the photon loses zero energy and ...
3
votes
1answer
152 views

S-matrix in Weinberg QFT

I'm a bit confused by Weinberg's discussion of scattering. He defined the in and out states $|\Psi^{\pm}_\alpha\rangle$ with particle content $\alpha$ as states that transform under the Poincare group ...

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