All Questions
219,566
questions
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Ventilated supercavitation formula
My goal is to build a model SWATH ship that uses ventilated disk cavitators, similar to the Juliet Marine Systems Ghost. To do so I would like to be able to create a 3D plot of speed, cavitator radius ...
- 1
0
votes
3
answers
85
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Why won't the bulb light? [closed]
Here's what the marking scheme says: "Capacitor gets charged first and acts as an insulator/blocks current".
However, electrons flow from negative to positive, so shouldn't the electrons ...
- 89
0
votes
4
answers
55
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Electric field definition
In my book it says that "electric field" is defined as the "force per unit charge". What does the "unit charge" mean? My initial thoughts was that it meant 1 Coulumb, but ...
- 89
0
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5
answers
76
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Different methods give different answers to the compression of spring [duplicate]
At first, I have to write down the scenario to represent my doubt properly.
Scenario: An ideal massless spring with a force constant of $k$ is kept vertically on the floor. Then a mass $m$ is kept on ...
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-1
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1
answer
27
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If 2 substances have same heat capacity and the same amount of heat is supplied to both which one will show a greater rise in temprature? [closed]
My textebbok says a substance with greater specific heat capacity shows a greater rise in temprature but if both the substances have the same heat capacity wont they show the same rise in temprature ...
1
vote
3
answers
43
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Buoyancy force vs object weight
If an object is floating (partially or fully), does the buoyancy force = the weight of the entire object?
My confusion is,
situation A: 100g object is 50% submerged and floating
situation B: 100g ...
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4
votes
3
answers
268
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How does Temperature of a system change if doing work on the environment? Can the temperature of the system increase?
I am just a bit confused about how to relate Temperature and work. If my system is doing work on the environment, could the temperature increase? I know that you can lower energy while raising entropy ...
- 51
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votes
1
answer
150
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What is the full QED Lagrangian with physics units written out?
I wonder what the QED Lagrangian would look like if you carefully write out all units of the terms and make sure they are consistent. I think there is something missing about Coulomb.
Can you write ...
- 1,397
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0
answers
28
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Spectroscopy features of noble gases
I notice that some people focus on the light spectroscopy of noble gases.
What difference will the closed shell make?
Are the noble gases simpler than other atoms when it comes to light-atom ...
- 1,495
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votes
1
answer
31
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How does narrowing and splitting/branching of a pipe affect speed of liquid flow?
What happens to the speed of a liquid in a pipe that is one of several branches that a larger diameter pipe splits into?
Here is a question in a practise booklet I want to answer:
"A horizontal ...
1
vote
1
answer
37
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Euler's equation of motion for rigid bodies rotating with one rotation axis not through the body's center of mass
this is my first question in this forum. Thanks for all the knowledge and support shared throughout the whole website!
I have a body with rotations around 3 axes. I am looking for the external torques ...
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1
vote
1
answer
36
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Proof that Fermi level is constant throughout a system in thermal equilibrium
The explainations I saw:
The one I was referring to in this question. I described why I find this explaination not satisfying in the question.
Consider $2$ systems in contact. The rate of particles ...
- 300
3
votes
0
answers
33
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Understanding the concept of hole in semiconductor physics [duplicate]
I've studied the Kronig–Penney model and learned about the effective mass theory and I know that at the top of the valence band the effective mass of electrons are negative, this is just an ...
- 283
0
votes
1
answer
18
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Center of Mass calculation in configuration of $3$ pennies inscribing equilateral triangle [closed]
I'm working on a problem that is asking me to solve the moment of inertia about the center of mass of a $3$ penny system where the edge of each penny is touching the edge of the others and the ...
1
vote
1
answer
40
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Peskin and Schroeder, Linear sigma model, renormalized perturbation theory
On Peskin & Schroeder's QFT pages 353-355, the book uses the Linear sigma model to illustrate the renormalization and symmetry.
We can write the Lagrangian of Linear sigma model with
$$
\begin{...
- 1,121
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votes
1
answer
23
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Electrons distribution when a conductor is placed in an electric field
(This is releated to the question of how electric field inside a conductor is zero, but Im trying to focus on a specific part of that expalnation in this question, I hope you understand).
Im ...
- 438
1
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0
answers
14
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Hyperfine structure of spectral lines
In hyperfine spliting of level, the order of hfs(hyperfine spliting) level in some hypermultiplts is normal(smallest
F level deepest) while in others it is inverted(largestF level deepest).what is ...
- 21
5
votes
1
answer
217
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Adjoint of the Quantum Momentum Operator
I'm studying quantum mechanics and I have a question about the momentum operator. We have that the momentum operator is given by
\begin{equation*}
p = -i\hbar\nabla
\end{equation*}
and so its adjoint ...
- 185
5
votes
1
answer
726
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Is an electron more stable than a proton/neutron?
Is an electron more stable than a proton/neutron under extreme temperature/pressure conditions, like several 100 millions K?
- 147
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0
answers
15
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Vacuum chamber end plate thicknees calculation [closed]
How to calculate the thickness of the flat covers used in the cylindrical vacuum chamber.
0
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0
answers
10
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Time dependency of displacement of a particle in a stationary wave [closed]
A question related to standing waves is given:
Stationary waves are produced by the superposition of two waves given by $y_1= 0.05 sin(5πt - x)$ and $y₂ = 0.05sin (5πt + x)$, x and y are in metres ...
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0
answers
22
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How to make the heating the water in paper cup experiment work? [closed]
The experiment is put water in a paper cup and put it over a flame and the water should cool the cup so it doesn't burn and even the water should even boil but I tried it with my stove and the cup ...
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votes
1
answer
39
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What's the direction of gradient vector in this situation?
Recently I came up with the grad vector in electrodynamics course where I read that it is a vector pointing in the direction of the maximum rate of change of the scalar field. This implies that given ...
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1
answer
62
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Book recommendation for classical Newtonian gravity
I’m looking for a good textbook that covers Newtonian Gravity in detail (preferably advanced undergrad/grad level). One that covers important things like
Calculating trajectories of satellites around ...
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3
answers
30
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Ways of losing energy of a bouncing objects in vacuum other than Heat and Sound
When we released a bouncing object in a vacuum chamber, the object will fall, contact the ground of the chamber and bounce back up. We know that the object will not return to its original height ...
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0
answers
8
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How does the density of puffed rice compare to polystyrene foam? [closed]
How does the density of puffed rice compare to polystyrene foam?
I was thinking that a mixture of puffed rice, pva glue, and bittering agent might be a biodegradable and more environmentally friendly ...
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0
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24
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Will this system conduct Simple harmonic motion? [closed]
Can you tell whether this system conduct Simple harmoniv motion or not?
If yes can you prove it in a simple way
Also " Will the angle made by both string with vertical same if we make Small ...
0
votes
2
answers
69
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Why chemical potential changes as a system approaches chemical equilibrium?
Consider a closed system of constant volume $V$, constant pressure $P$, temperature $T$, and Gibbs energy $G$ that is in thermal and mechanical equilibrium with surroundings. It is filled with $N$ ...
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1
answer
39
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How does 0 electric potential but non-zero electric field work mathematically
I've been trying to figure this out on my own for days and finally decided to start googling. For reference I'm self studying Griffith's E&M textbook. I'm at the part where he derives the equation ...
3
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0
answers
32
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What is the explanation for the structure of foam?
When you look at any gas in liquid foam, you'll see a particular structure.
You'll find that the structure consists of some bigger bubbles along with some smaller and smaller ones.
I would like to ...
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38
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How to approximate $\exp(-t(A-B))$ for diagonal $A$ and rank-1 $B$? [migrated]
I have $d\times d$ diagonal matrix $A=\operatorname{diag}a$ and rank-1 $B=b b^T$ and need to efficiently approximate the following function:
$$f(t)=\langle\exp(-t(A-B))\rangle$$
Here $\langle M \...
- 193
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votes
1
answer
31
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Charge distribution on a discharged conductor
Question
I am trying to prove that given a conductor with zero net charge on it then the charges necessarily distributes on its surface so that the density is zero at every point.
We can assume the ...
- 356
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votes
2
answers
50
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Different kinds of energy Are they relative?
I'm not sure if this is a physics-based question. There are many kinds of energy in physics.
For example, kinetic energy, potential energy, thermal energy, electrical energy
Magnetic energy, radiant ...
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60
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What is Singlet Fermion?
I encountered this term in the paper Singlet fermionic dark matter by Yeong Gyun Kim et al regarding Dark Matter. From my quantum mechanics knowledge singlet would refer to a singlet state which is a ...
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1
answer
37
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Why does the radius of orbit increase when a satellite increases it's velocity?
Can someone please explain to me why increasing the velocity of a satellite with a rocket booster will change the radius of the orbit rather than the linear velocity of the satellite? If the angular ...
0
votes
1
answer
46
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How does a gas giant planet hold it's spherical shape when it has tidally locked rotation in it's orbit around the Sun?
How does a gas giant planet hold its spherical shape when it has a tidally locked rotation in its orbit around its Sun? Wouldn't it fall apart without its gravitational pull from the rotation? How ...
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0
answers
23
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Why does the intensity get low when the frequency gets high according to the Planck Diagram? [closed]
In my text book it states that the intensity should be very high for high frequencies however in the diagram it shows very low intensities. I know it has something to do with the quantum effects but I ...
-1
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0
answers
26
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Accurately turning spectral lines of elements into audio [closed]
This video uses the sum of the sin waves of the Lynman and Balmer series to obtain the "audio" of Hydrogen. To get a more accurate representation, should all the sin waves of hydrogen ...
0
votes
2
answers
93
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Possibility of anti-time
I was just wondering if every particle has an anti-particle (or so I've read/heard), are there other things which could be candidates to have an anti- "form" as well? My example is focused ...
-5
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0
answers
81
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General Relativity paradox [closed]
General Relativity is based on the equivalence principle which says that inertial and gravitational mass are the same.But we can pick a reference frame for any massive planet such as its inertial mass ...
-3
votes
1
answer
53
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Is the electron in two places at once in Stern Gerlach experiment? [closed]
Before measurement the electron is in superposition of up down spin projection but every projection moves in its own path. So the electron must be in two places at once. Right?
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0
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12
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Holding two 3X lenses on top of each other, how much magnification does this give me? [closed]
Quick optical question, to do with zoom lenses. Assume this refers to magnifying sheets such as in the image below.
Say it's a 3X zoom. Now say the user still doesn't find it to be enough, and so ...
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1
vote
5
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145
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Why do wires attract when they carry current in the same direction (in relativistic sense)?
I have seen the veritasium video on this subject (https://www.youtube.com/watch?v=1TKSfAkWWN0), but I have this question which am unable to find the answer for.
I have 2 wires carrying same current in ...
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2
votes
1
answer
67
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Why are the microstates of a harmonic oscillator considered equally probable, when the particle spends more time at locations of zero momentum?
Introductory statistical mechanics for a microcanonical ensemble (a.k.a. constant energy, no exchange of heat or work with environment) claims that all microstates in the momentum–location phase space ...
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1
answer
47
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Summing graphs in the partition function (statistical physics)
I am looking at Tong's lecture notes on statistical physics, and I wanted to understand a step in his cluster expansion better.
The goal here is to calculate the partition function in the canonical ...
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1
answer
54
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Max value of I in a circuit
I am a EE student.I have been taught Ohm's law which says $I = \frac{V}{R}$.In the limit of$R \rightarrow 0,I \rightarrow \infty$.But I have also taken the course "Electromagnetism II" where ...
0
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1
answer
14
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Stacking of magnetic moments in a polarised neutron beam
Neutrons are particles that have a half spin and a magnetic moment. if you polarise a beam of neutrons so that they all align with spin +1/2 will the combined neutron beam have an overall magnetic ...
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0
answers
32
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How does the center of mass change during an inelastic collisions? [closed]
Let's say a uniform rod is rotating around one end fixed to a table by a nail. Then let's say a disk (a uniform point) collides with the rod and stays attached causing the rod to experience some ...
0
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0
answers
63
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Momentum operator in spherical coordinates
In the position representation the momentum operator takes the form of the gradient, $-i\hbar \nabla$.
It is understood that its components denote $p_{x}, p_{y}, p_{z}$ respectively; but, when ...
0
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1
answer
34
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Is the rate of radioactive decay inversely proportional to the stability of an isotope?
Is the rate of radioactive decay inversely proportional to stability of the isotope?
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