# Tagged Questions

Scalar and vector potentials in electromagnetism. The scalar potential is potential energy per unit charge. For potential energy, use the potential-energy tag.

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### Why is the ground state energy of a 2DEG higher compared to the 3DEG?

I am reading something about a 2DEG (2-dimensional electrongas model) and can not understand it. My book says the ground state of the 2DEG is higher compared to a 3DEG because the confinement to 2D ...
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### Can Ampere's Circuital law be used on an infinite number of alternating Helmholtz coils?

I have the following surface current density $$\bar{\sigma}_s = \hat{\phi} \sin(kz) |\bar{\sigma}_s|$$ to approximate an infinite number of alternating Helmholtz coils stacked along the z-axis with ...
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### Why does the potential difference between two charged plates increase as they move further apart?

Suppose a uniform electric field $E$ exists between to oppositely charged metal plates (one is positively charged and one is negatively charged). If the plates move apart, and the charges on each ...
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### Why does the sphere with the smaller radius (r1) have the greater charge density?

Suppose two charged conducting spheres of different radii $r_1$ and $r_2 > r_1$ are very far apart but connected by a conducting wire. Why does the sphere with the smaller radius $(r_1)$ have the ...
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### Dipoles and Potential Energy

I was pondering about electrostatics, particularly dipoles. How would one go about calculating the difference in potential energy of a dipole an arbitrary distance away from an arrangement of another ...
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### Calculating the potential of 2 spherical perfect conductors with the image method

I am searching for a way to calculate the potential on the surface of two perfect conductors that are spheres. I am not sure my method is correct. Here is a diagram of what I am studying : They ...
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### Kinetic energy and Potential of a photon

How does the potential and kinetic energy of a photon relate? Do they mean the same thing? Also how does De broglie wavelength and Potential relate?
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### Electric potential at midpoint?

I understand that if you assume the field is uniform between R and S then you can use E=V/d to get E=(30-20)/(0.5)=20Vm^(-1), so the answer is C (which is correct according to the mark scheme). But ...
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### Calculation & derivation of de-Broglie wavelength [duplicate]

How to calculate the de Broglie wavelength of an $\alpha$ particle that is accelerated through a potential difference of $V$ from rest.
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### Need help on electric potential definition

I'm having trouble understanding electric potential. In my book it says "an electric force acts on a charge situated in an electric field." I understand this part. Then it goes on to say "If a charge ...
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### Why is the zero of electric potential taken to be $r = \infty$, rather than $r = 0?$

Wouldn't it make more sense if it was taken to be zero at $r = 0$? This seems to imply that with a negative test charge at $r = 0$ from a positive point charge, $V = -\infty$, which I have trouble ...
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### A Method of Images Problem from Electrodynamics (Cylindrical Surfaces)

This problem is from Introduction to Electrodynamics 4th Edition , Griffiths, problem 3.12 Two long, straight copper pipes, each of radius $R$, are held a distance $2d$ apart. One is at potential ...
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### How to determine if a potential admits bound states?

According to Griffith's Quantum Mechanics, "$E$ must exceed the minimum value of $V(x)$, for every normalizable solution to the time independent Schroedinger equation" As an example, there is no ...
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### At what distance is lightning dangerous for someone lying down?

My 8 yo child told me that they learned at school that they should lay down flat on the ground in case of lightning. I told him that the more correct position is crouching down with feet together, but ...
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### How do the electrons know the route? [duplicate]

I've learnt in classroom that the requirements for electrical current to flow in a circuit are as follows: there must be a closed conducting path between negative and positive terminals there must ...
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### What state does the particle in a box occupy?

My textbook derives the equations for the different energy states $E_n$ of the particle in a box. But my professor in class said this example was a good one because it spoke about the "superposition ...
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### Why do we not require higher derivatives to match at boundary when solving the Schrödinger equation in a given potential?

When solving the time independent Schrödinger equation for a given potential in 1D, the main part of the solving involves matching boundary conditions. Usually, we require the value and the first ...
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### How can I physically demonstrate potential difference in a circuit to a 14 year old?

Children of this age have a fair idea about current, resistance, and batteries. Potential difference is a thing that cannot be felt or physically visualized. A teenager asked me if he can touch ...
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### Use of termination in solving quantum harmonic oscillator, hydrogen atom etc

I can't seem to understand the use of termination to make the series solutions physically acceptable (when solving the linear harmonic oscillator etc.). So what if the series does not terminate, it's ...
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### Calculating the electric charge of two spheres knowing their potential

I have a system of two spheres, the first one is at a potential of $V_1 = 1 V$ and the second one is at a potential of $V_2 = 0 V$ The distance between them is $d$ and the radius are respectively ...
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### Infinite Energies of a particle in a rectangular box

For a particle trapped inside a rectangular box of side lengths $l_x$ $l_y$ and $l_z$, the energies are ...
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### Potential of a sphere induced by a charged sphere

I am trying to solve what seems like a simple problem but something is bothering me: Imagine we have a sphere (1) with a charge $Q_1$ and at a distance $d$ we have another sphere (2) which is a ...
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### Why the electrons flow from higher potential to lower potential?

We know that every thing moves from a higher potential to lower potential. In fact we also studied in our textbooks that a charge travels from higher potential ie. Positive side to lower potential ie. ...
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### Aharonov-Bohm experiment: A possible way to understand potentials?

I'm posting this question as a function of an another question I found here: What is potential energy truly? The answer of WetSavannaAnimal aka Rod Vance. As I understand the hole point is to see ...
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### Physical interpretation of single layer potential in the plane

Let $\Omega\subset\mathbb{R}^2$ be a bounded domain with smooth boundary $\partial\Omega$. The single layer potential with charge density $f$ sitting on $\partial\Omega$ is defined by ...
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### Potential and kinetic energy

If a ball stays on the ground, it has no height and no velocity. So what energy does it have kinetic or potential?
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### Potential of a uniformly charged hollow sphere [closed]

If I use Gauss' theorem I find that, for $r\geq R$ $$V(r) = \frac{\sigma R^2}{\epsilon_0 r} = \frac{Q_{sphere}}{4\pi\epsilon_0r}$$ where $\sigma$ is the surface charge density and $R$ the radius of ...
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### Particle in a one dimensional box conditions

Why does the wave function have to be $C^1(\mathbb{R})$ for a finite square well but not for an infinite square well? For an infinite square well with boundaries at $x=0$ and $x=L$, we have ...
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### Classical Hall effect when current has neutral charge

Suppose I have a current of both negative and positive charges(I know that there is also current from only negative and only positive charges,I'm not confused) along an infinite wire of square ...