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1answer
27 views

Finding the potential between two spherical shells [on hold]

How to find the potential in region $a<r<b$ I know that the general solution for Laplace's equation is $$V(r,\theta)=\sum_{l=0} \left[A_l r^l +\frac{B_l}{r^{l+1}} \right]P_l(\cos{\theta}).$$ ...
3
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1answer
105 views

1D Finite potential well: solutions with $\sinh$ and $\cosh$?

So I am studying the (one dimensional) quantum mechanical finite potential well defined by: $$ V(x) = \cases{0, &|x|>a\cr -V_0, &|x|<a} $$ where $V_0>0$ is a real number. I know ...
-1
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0answers
36 views

Lennard Jones potential is bad in my plot made with python [closed]

Note that this question is about formula, not about code debugging. I made a program which draws LJ potential with parameters gamma and sigma adjusted with sliders in GUI. However regardless what ...
1
vote
1answer
29 views

Electric Potential-can anyone give the concept behind this?

Three points A, B and C lie in a uniform electric field (E) of 5 x 103 NC-1 as shown in the figure. Find the potential difference between A and C. I think there is some trick? How can the pd ...
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1answer
25 views

Why are the dineutron and diproton unbound?

It is known that there is no diproton and dineutron nuclei. Does this mean that two protons or neutrons are not actually attracted to each other? Even if the attraction was weak, wouldn't it cause ...
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0answers
16 views

What does it mean to charge a length of wire up to potential v?

I have to study the text "On the Theory of the Electric Telegraph," By William Thomson, 1855. I am having trouble gaining a conceptual understanding of the opening: "Let c be the electro-statical ...
0
votes
1answer
20 views

Potential Difference of a wire?

Imagine a circuit with only a 12 Volts battery and a wire connecting the ends of the battery. Point A and point B lies on the wire. What is then the potential difference between point A and B if the ...
1
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1answer
63 views

Bohr-Sommerfeld quantization for different potentials

Let's have Bohr-Sommerfeld quantization for one-dimensional case: $$ \int \limits_{a}^{b} p(x)dx ~=~ \pi \hbar (n + \nu ). $$ Here $p(x) = \sqrt{2m(E - U)}$, $a, b$ are turning points, and the area ...
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2answers
54 views

Semiclassical quantization of bouncing ball

Consider an elastically bouncing ball of mass $m$ and energy $E$. This has a triangular potential $$ V(x)~=~\left\{\begin{array}{ll} mgx & \text{if } x>0, \\ \infty & \text{if } x<0, ...
0
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0answers
14 views

Tersoff parameters

I am studying the tersoff potential i am trying to understand the physical meaning for each parameters in this potential. The development of Tersoff potential is a little fuzzy (several articles). ...
0
votes
1answer
35 views

Ignoring constant potential energy

The reason why constant potential energy terms are dropped is because the derivative of a constant is zero. And since force is the gradient of potential energy, constant terms won't change what the ...
1
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1answer
51 views

How to find an effective spring constant of a quadratic potential

If a potential energy is given like $U(r)=A^3/r^2+2B^3r$, how do I find the effective spring constant using Taylor Expansion? I compared spring constant $k$ to be equal to second derivative of ...
1
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1answer
32 views

Lagrangian of Non-Relativistic Charged Particle in a Magnetic Field

I'm trying to derive the Lagrangian for a non-relativistic charged particle under the influence of a magnetic potential. I'm assuming that $F=-grad(V)$ and so by the Lorentz force we have $-grad(V)=q ...
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0answers
24 views

Solving of one dimensional potential sets [closed]

is a set of 1D potentials which i need more examples and their solutions containing transmitting states, bounded states, scattering states and coefficients. I searched with 1D potential ...
1
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0answers
30 views

Flow in the strip $0 < x < \pi/2$, $y > 0$ [closed]

Could anyone please explain how to show that a complex valued function represents a flow? For example, how does one show that $\Phi(z) = \sec^2 z$, where $z = x + iy$ with $x, y \in \mathbb{R}$, ...
6
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4answers
252 views

Why the statement “there exist at least one bound state for negative potential” doesn't hold for 3D case?

Previously I thought this is a universal theorem, for one can prove it in the one dimensional case using variational principal. However, today I'm doing a homework considering a potential like ...
0
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1answer
37 views

Electric field and potential between two charges [closed]

There are two point charges on the $x$ axis and $x'$ is a place where the potential, relative to infinity, is the biggest. Why is the electric field zero at this point?
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votes
3answers
66 views

Voltage in a parallel circuit [duplicate]

Why is voltage same across a parallel circuit? I mean what makes the voltage remain same across two resistors connected in parallel? If an electric heater is connected in parallel with a bulb and ...
-2
votes
1answer
71 views

Quantum mechanics: Finite square well problem

What will happen if the potential is less than 0, for instance $V(x)=-10eV$. Is this means there will be no bound states? Since solution to the time independent Schrodinger equation (those discrete ...
0
votes
1answer
21 views

Finding voltage between two points in space

If electric field vector is defines as : $\vec{E} = \frac{V_0x^2}{a^3} \vec{i_x} + \frac{V_0y}{a^2} \vec{i_y} $ where $V_0 $ and $a$ are known constants, $\vec{i_x}$ and $\vec{i_y}$ unit vectors of ...
2
votes
1answer
78 views

Inconsistency in the delta potential

I encountered an inconsistency in the one-dimensional delta potential. Suppose we have a one-dimensional infinitely deep square well from $-L$ to $+L$. We know the eigenstates are sine and cosine ...
3
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2answers
246 views

1D Infinite Square Box Discrete Energy levels but Continous Momenta?

In the 1d particle in the box the energy of the particle should be completely determined by the momentum of the particle that you observe correct? So how can you have discrete energy levels and a ...
3
votes
3answers
90 views

What is the physical meaning of electric potential, potential difference, and voltage?

When resembling the electricity flow through a wire to people walking through a street: electrons are people, current is the number of people, resistance is the barriers on the way. But what is the ...
0
votes
1answer
37 views

Introductory Quantum, trouble with this boundary condition and potential

Working on problem 2.40 from Griffiths but can't seem to understand the first boundary condition. We are given the potential $V(x) = \left\{\begin{matrix} \infty & x < 0\\ ...
0
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1answer
50 views

Scattering and bound States

So from my understanding, as long as $E>0$ you will have scattering states and these scattering states will always result in an imaginary $\psi$, but bound states can also have an imaginary ...
2
votes
1answer
91 views

Railguns and Gauge Invariance

Paul J. Cote and Mark A. Johnson of Benet Laboratories, Army Research, Engineering and Development Command wrote a series of short papers on the vector potential arising from their attempts to solve ...
0
votes
1answer
51 views

What is a Hulten potential?

What is the Hulten potential? When is it used? How is it derived? I vaguely heard about in the context of neutron synthesis / quantum mechanics. thanks
1
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1answer
58 views

Is the Gibbs-Duhem equation always valid?

The derivation of the Gibbs-Duhem equation from Wikpedia uses: As shown in the Gibbs free energy article, the chemical potential is just another name for the partial molar (or just partial, ...
1
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1answer
35 views

Help regarding understanding derivation of electrostatic potential in a solution to a problem

I was looking at the solution of finding the energy stored in a charged solid sphere in which the electric field was and then later stated the electrostatic potential is I understand that to ...
2
votes
3answers
90 views

How come we talk about gravitational potential energy and not gravitational potential?

With regards to gravity the equation learned is $$U=-\frac{GMm}{r}$$ And the relationship to force is $$F=-\frac{dU}{dr}$$ In electrostatics we instead talk about electric field and electric ...
1
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1answer
165 views

Particle Outside the Box

What prohibits, mathematically, that a particle cannot be found outside the box ? Here, I am referring to particle in a box problem (infinite potential on both ends & zero potential along the ...
1
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0answers
38 views

What is “W external” and “W internal” in Energy conservation law?

When I solve the energy conservation problem, I am confused when I have to make the term positive or negative. For example, someone throws a ball right up to the ground with velocity, $v$. The ball ...
1
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2answers
91 views

System without ground state is not real in nature?

We know that Coulomb force is real phenomena in nature and with Coulomb potential $V(x) \thicksim -\frac{1}{|x|}$ lowest energy is bounded in hydrogen atom. But it's mathematically clear that if ...
1
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1answer
77 views

Degeneracy in One Dimension

I'm reading this wikipedia article and I'm trying to understand the proof under "Degeneracy in One Dimension". Here's what it says: Considering a one-dimensional quantum system in a potential ...
0
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0answers
23 views

Meaning of negative effective range

In a case of a square-well potential the effective range and the scattering lenght depends on the characteristic parameter of the potential (see the explicit formula here, eq. 25a,25b ) and the plot ...
0
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0answers
33 views

What is the functional shape assumed by a flexible rod?

Be L a flexible rod. Say that it is very difficult to significantly stretch it, so that we can uniquely identify a point on it by a parameter $l \in [0, L]$ where $L$ is its length. Be $C$ a set of ...
3
votes
1answer
81 views

Potential that is proportional to distance

Does anybody know of a treatment of the case where a potential field is proportional to the distance, i.e. in 3 dimensions: $$V(\vec{r}) ~\sim ~ |\vec{r}|~?$$ Essentially the question is: What are ...
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votes
3answers
96 views

Why airports are generally near sea? [closed]

The generic way to measure the height is from the sea-level. If the airport is near the sea i.e. not at a very height from the sea, then the fuel required to make the air-plane above the sea level ...
1
vote
1answer
38 views

General potential of rotating system

I'm new here at the physics site, and not really that deep into the area of which i'm going to ask a question about now. Therefore please feel free to ask clarifying questions. I'm trying to deal ...
1
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1answer
19 views

Electrohydrodynamics: How will electric potential develop in a fluid when potential is applied from ends

Lets say, I have a fluid in a rectangular enclosure (2D). I apply electric potential $U=U_1$ at left boundary and $U_2$ at right boundary. In the lower and upper boundaries, the potential varies ...
1
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2answers
78 views

Definite energy states for a single non-relativistic particle with a time dependent potential

Do definite energy states exist for a single particle when its potential itself changes with time? I tried solving it and the equations seem to show that they do not exist. But then i am confused as ...
0
votes
1answer
18 views

How is electric field strength related to potential difference?

I was looking at the derivation of drift velocity of free electrons in a conductor in terms of relaxation time of electrons. Here a metallic conductor XY of length $\ell$ is considered and having ...
1
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0answers
44 views

What is the physical meaning of the norm of the electromagnetic four-potential?

In SI units this would be $\frac{1}{c^2}\phi^2 - A_x^2 - A_y^2 - A_z^2$. Is this just not a physically meaningful quantity at all because it's not gauge invariant?
1
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1answer
41 views

Mass of small fluctuation around vacuum

For a potential $V$, how do we define the mass of a small fluctuation around its vacuum? For example I have the potential $$ V_\mathrm{eff}(\phi) = \frac{1}{2} \left(\frac{\rho}{M^2} - \mu^2\right) ...
0
votes
3answers
68 views

What does raising voltage do?

If I raise the voltage of a wire from 0V to 1000V and then to 5000V, am I merely packing it with more and more electrons (with those electrons being trapped there until they find a path off the wire)? ...
0
votes
3answers
322 views

Potential difference between point on surface and point on axis of uniformly charged cylinder

Question: Charge is uniformly distributed with charge density $ρ$ inside a very long cylinder of radius $R$. Find the potential difference between the surface and the axis of the cylinder. Express ...
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0answers
26 views

Nonlocal interaction effects on bose-einstein condensates

I'm studying an interacting bose-einstein condensate using the energy functional proposed in this paper K. Huang, C.N. Yang, Phys. Rev. 105 $$ E\left[\phi\right] = \int d^3\vec{r} ...
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0answers
81 views

The Effect of Tortoise Coordinates

Referring particularly to http://arxiv.org/abs/hep-th/9909056 in regard to the wave equation for Schwarzschild-AdS black holes (p.4), I'm trying to understand tortoise coordinates. So starting ...
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2answers
50 views

Special case of work done by two opposing forces of equal magnitude on a body possesing inertial motion

Consider an elevator moving upward with constant velocity. The constant velocity is maintained by an upward tensional force equal to weight. If we add the total work done on the elevator it will be ...
3
votes
1answer
51 views

Why is electric potential positive?

If there is a positive charge $q$ at the origin of a coordinate system, the electric potential $\phi$ at a distance $r$ from $q$ is (by definition, if we take the point of zero potential at infinity): ...