0
votes
0answers
2 views

Gravitational entropy

In the beginning (big bang), mass was evenly distributed (if you consider an elementary particle as an extended object, like a circle on a very thin cylinder, with a radius near the Planck length, but ...
0
votes
0answers
3 views

How to find the force of a magnetic field, resolving the components?

So, in answering this question the book resolves the components of the Force vector in this manner; (1) dFx= dF*$\sin \theta$ (2) dFy= dF*$\cos \theta$. And then, it integrates from $\theta_0$ to ...
0
votes
0answers
4 views

Semileptonic decay of neutral D meson: branching ratios?

I am looking for the branching ratio of the semileptonic decay of the neutral $D^0$ meson: BR($D^0 \to \pi^+e^-\bar\nu_e$) = ? According to the PDG book the branching ratio for $D^0 \to ...
0
votes
0answers
6 views

How do they know their speed in a spaceship?

Suppose a spaceship is going to Mars or to Jupiter, they switch on their propellers and accelerate for a certain period, how to they know their speed?
0
votes
0answers
5 views

newman janis algorithm ( schwarzschild to kerr metric)

my question is how to find the null tetrad for the schwarzschild metric in Eddington-finklstein coordinate ? pic 1: i only get the last two values but not able to find the first two tetrad values ...
1
vote
5answers
18 views

The Kelvin-Celsius problem

Let's suppose we have temperatures 30°C and 35°C. Converting them to Kelvin we have 303.15K and 308.15K. In the second case, the temperature difference is 5K. While in first case, temperature ...
1
vote
1answer
12 views

What does it mean that a Cooper pair behaves as a boson but respects the obligations of fermions?

I refer to the fact that it has integer spin, but antisymmetric wavefunction. How is this possible?
1
vote
1answer
20 views

Is this video's notion of general relativity correct?

In this video it explains the path of the apple in the general relativity version of gravity as being a straight line on a curved surface. Is this valid?
0
votes
2answers
28 views

What ds>dQ/T mean?

I read the derivation on page 216 over here: https://www3.nd.edu/~powers/ame.20231/notes.pdf First it considers an irreversible process between state 1 and 2 followed by a reversible process between ...
0
votes
0answers
10 views

Momentum conservation problem, elastic collision [duplicate]

This question has got me thinking for a while now and I haven't been able to come up with any answer at all. I've done the basic conservation of momentum, kinetic energy but I have no idea how to ...
1
vote
5answers
24 views

Brightness of 2 Lightbulbs hooked up to Capacitor

The figure shows a circuit consisting of a battery, a switch, two identical lightbulbs, and a capacitor that is initially uncharged. a. Immediately after the switch is closed, are either or both ...
1
vote
1answer
12 views

The energy of de-excitation

I am 10th class student and what i dont get is when electron dexcites it produces energy but what is main phenomenon which produces energy is it the motion of electron or something like disturbing ...
1
vote
0answers
20 views

Calculating the expectation value of spin

Consider the state-space with a base formed by the eigenstates of the operator $\hat{S}_z$. For the state $|\phi\rangle=\frac{1}{\sqrt2}|+\rangle_z-\frac{1}{\sqrt2}|-\rangle_z$, what is the value ...
0
votes
1answer
18 views

Trouble understanding a formula in Turbulence

I'm very new to turbulence.I'm reading this book on "Turbulence: An introduction for scientist and Engineers" by Davidson. I came across this formula for energy dissipation. This is in chapter one. I ...
1
vote
3answers
43 views

When to use Quantum Mech.?

Is there any parameter (in terms of physical quantities such as mass, length, charge...) which can be used to decide when to treat a system quantum mechanically and not classically?
1
vote
1answer
22 views

Variation of Veritasium bullet block experiment

I'm new here. this is in reference to the video posted by veritasium on the bullet block experiment. i realise there is already a thread on this but i want to ask a variation of the question. so ...
1
vote
3answers
19 views

When does the Boltzmann distribution apply?

What are the requirements for a system to be described by the Boltzmann distribution in equilibrium? For example, should all the particles be identical? No attractors in the phase space? ...
1
vote
0answers
24 views

What is the volume of water displaced by the oak object? [on hold]

This is a problem from my physics assignment. The question didn't mention the mass of the oak object, making this problem really confusing. Here's the problem: A 100mL oak object is placed in water. ...
-1
votes
0answers
3 views

Circuit Board AND/decade counter [migrated]

What output do I use to connect the decade counter to the AND chip? I'm confused as to what pin to use to output to the AND chip? I've circled where I need to connect the AND chip and the decade ...
0
votes
3answers
43 views

Does an electromagnetic wave necessarily contain many photons?

I've often come across people saying from a quantum physics standpoint that an electromagnetic wave necessarily contains many photons. But doesn't the double-slit experiment conducted one photon ...
1
vote
0answers
8 views

Why the bandgap of inorganic semiconductors decreases with temperature?

The temperature dependence of the energy bandgap in inorganic semiconductors is given by $$E_g (T) = E_{g,0} - \frac{\alpha T^2}{T+\beta}$$ where $\alpha, \beta$ are both positive, and the (somewhat ...
1
vote
1answer
24 views

Conditions for free fall

What are the conditions at which free fall occurs? If a body is falling freely under the effect of gravity only without external resistance, the motion is called free fall. This definition gives me ...
1
vote
2answers
34 views

Mathematical treatment of electron double slit experiment

Can someone please provide me with the mathematical treatment of the double slit experiments with electrons? The diffraction pattern seems to resemble that generated by photons (light) counterpart, ...
0
votes
1answer
32 views

Definition of the Lorentz transformations

Until very recently I believed that the Lorentz transformations were defined as "the transformations that carry one inertial reference frame into another". In Wikipedia's page we find something along ...
1
vote
1answer
36 views

Acceleration due to gravity [on hold]

Why is it difficult to drink water inside the artificial satellite in the space? I think one of the reasons is that there is no gravity in space and hence we cannot drink water. but I am not sure ...
0
votes
0answers
9 views

Classical space-time and quantum indiscernibility

Non-relativistic QM works in Newtonian space-time. Does the representation of a quantum system in this setting individualizes it in such a way that this conflicts with the non-individuality and the ...
-1
votes
1answer
21 views

Is there a software to convert units for quantities and equations? [on hold]

For example, Often I end up with a complicated equation that uses nonstandard units. In these equations, Temperature is in eV and Magnetic field is in Gauss. I need to convert my equation to another ...
0
votes
1answer
27 views

How do you calculate the expected force of an electromagnet?

What is the equation to find the expected force of electromagnet? What do the variables mean and how do you find each variable?
1
vote
2answers
24 views

Why do people say that 'power flows' into or out of a component in an electric circuit?

Currently, I am learning about electric circuits, and how to apply the basic concepts of physics, like work and energy. But I keep running into the same phrase--on Wikipedia, my textbooks, ...
0
votes
0answers
13 views

Reverse osmosis Water desalination

Is it feasible to submerge a reverse osmosis system in the sea in order to use the increasing pressure to push through the membrane and as the salt was removed would the lighter water rise on its own? ...
0
votes
1answer
9 views

Approximating magnetic field at center of current loop by solenoid of 1 turn

It's well known that by application of biot-savart law, the magnetic field at the center of a loop of current is $\frac{\mu_0 I}{2r}$. Now when we consider a solenoid, isn't the resulting magnetic ...
-2
votes
0answers
15 views

Rotation operator adjoint multiplication

Why does the last term equal 0(d$\phi^2$)?
0
votes
1answer
37 views

How do you find the electric field corresponding to the magnetic field?

If we are given the magnetic field $B$ how can I find the corresponding electric field? The example brought up at the end of my lecture was $B = B_o \cos(ky-\omega t)$ in the $k$-direction. I am ...
0
votes
0answers
16 views

Why does some peoples' hair look blue when I look out the train window while wearing sunglasses?

Specifically, when I look through the window, black hair looks blue when people pass the window outside, and black shiny benches look like somebody painted them blue. Pretty sure my sunglasses are ...
-1
votes
0answers
20 views

Variational Method for one dimensional infinite square well

I have an one dimensional infinite square well of width $a=1$, and I want to use variational method to produce the ground state energy. My trial wavefunction is ...
-1
votes
0answers
18 views

physics thermofluid mechanics pressure force area

As shown in the attached image, a tank has an inclined wall at an angle of $45^{\circ}$ to the horizontal. On this wall, there is a 1 m square door that is hinged at A and has a simple latch at B. The ...
6
votes
1answer
48 views

Tensor product - Addition of angular momenta

In the book Quantum Mechanics - Cohen-Tannoudji, in chapter X, equation (B-5) says $$ \vec{S^2} = (\vec{S_1} + \vec{S_2})^2 = \vec{S_1^2} + \vec{S_2^2} + 2\vec{S_1}\cdot\vec{S_2} $$ and $$ ...
0
votes
0answers
12 views

How strong is the HCN Union when modelling with springs

I'm modeling the HCN Molecule with springs, giving the bounds between H and C the name k1 and between C and N k2. Is there any information of how strong is the bound? We were asked to get the ...
0
votes
0answers
11 views

Graph of Thermistor against Temperature [migrated]

Assume that I had a circuit as such above. I was wondering, if I increased the temperature of the surroundings, what would a graph of the temperature/PD graph look like? I know that Resistance ...
0
votes
0answers
16 views

How to find the width of a sinc function?

I took the data of visibility by varying the distance between two slits in the YDS experiment. I plotted the visibility vs the distance between two slits and fitted with sinc function. The width of ...
2
votes
1answer
15 views

Two Robertson-Walker observers, at what time will a light signal be received?

Here is a question I have that is inspired by this question here. The spacetime metric of a radiation-filled, spatially flat ($k = 0$) Robertson-Walker universe is given by$$ds^2 = - dT^2 + T[dx^2 + ...
0
votes
0answers
30 views

Why is this wrong? [on hold]

All surfaces are frictionless. My aim here is to relate the two accelerations. Why is $a_1\sin\theta = a_2$ i.e the horizontal component of $a_1 = a_2$ wrong? I know that the correct answer is $a_1 ...
3
votes
2answers
45 views

Is static friction the only force causing a car to move (without sliding)?

A car is moving without sliding means that the friction between wheels and the ground is static friction. This is the force causing an object to move forward, therefore, its direction is the same as ...
0
votes
1answer
44 views

Spring pendulum system [on hold]

Find the Lagrangian and the equations of motion for the system described by the figure using the Lagrange multipliers method. The mass $m$ can slide frictionless along the massless rigid rod of the ...
1
vote
3answers
50 views

Why can't the wave model for radiation cannot account for the photoelectric effect?

While I understand the effect of varying wavelength and frequencies on the photoelectric effect, I can't seem to turn my mind around that question... I suspect it has to do with quantas and the non ...
0
votes
1answer
34 views

Thermofluid mechanics inclined plane

As shown in the attacked image, a tank has an inclined wall at an angle of 450 to the horizontal. On this wall, there is a 1m square door that is hinged at A and has a simple latch at B. The distance ...
0
votes
3answers
24 views

Components of gravity in an inclined plane

The reason the block accelerates down the inclined plane is that the resultant of $N$ and $mg$ acts down the incline. However, why is the force causing the block to accelerate down the incline often ...
1
vote
2answers
33 views

Why does a ball eventually stop?

I was wondering, if the force of friction with the ground does not make any work on the ball and just give it the necessary torque to rotate (hence the consideration of static friction coefficient in ...
-3
votes
0answers
28 views

Dark energy and magnetic field [on hold]

I have learned that a photon creates it's own magnetic field. Arno Penzias & Robert Wilson discovered the background radiation from the Big Bang. Could this also be the time of the creation of ...
1
vote
1answer
50 views

What do the batteries actually do to the electrons?

I am plagued by this simple question that what force exactly causes the motion of an electron in the middle of a lattice of electrons of a wire? a. Is it an electric field created inside a wire due to ...

15 30 50 per page