# What is Coulomb: Definition and 231 Discussions

The coulomb (symbol: C) is the International System of Units (SI) unit of electric charge. Under the 2019 redefinition of the SI base units, which took effect on 20 May 2019, the coulomb is exactly 1/(1.602176634×10−19) elementary charges. The same number of electrons has the same magnitude but opposite sign of charge, that is, a charge of −1 C.

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1. ### B Understanding the Relationship Between Coulomb and Ampere in Physics

Hi! Why coulomb is not a base unit in Physics, but the Ampere is (and ampere is coulomb/s)? Isn't it like saying that m/s is a base unit? Can someone explain it to me?
2. ### A Potential Energy of Relativistic Particles in Coulomb Field

Let us consider relativistic particle (electron) which moves with relativistic speed ##v## in the Coulomb field (in the field of a fixed heavy nucleus). The main question is what is the potential energy of a particle in such a static field? Landau and Lifshitz in their book "Field Theory"...
3. ### Relativistic correction to Coulomb Potential in SQED

I have derived the Coulombian potential as an effective potential between two spinless charged particle taking the non-relativitic approach on the scattering amplitude obtained in terms of the Feynman rules in SQED. The scattering amplitudes are: I'm using the gauge in which xi = 1. How could...
4. ### B Coulomb pressure and concentric spheres

Suppose you have a sphere of radius a of positive charge, and a concentric shell from a to b of negative charge. The positive charge is equal to the negative charge. (non-conducting, uniform density) Is there an outward pressure at a of kqq/a2/(4πa2) - with pressure decreasing with radius...
5. ### I The atomic Coulomb potential extends to infinity?

I'm studying nuclear physics in a text, but at one point that is said: "Both the Coulomb potential that binds the atom and the resulting electronic charge distribution extends to infinity" , I don't understand what is that "resulting electronic charge distribution extends to infinity" what they...
6. ### Help with Coulomb's law: Net electrostatic force

I tried just calculating the force with Coulomb's law, then calculating the forces for each vector individually and adding, but I got it wrong both ways
7. ### Phase shifts for a localized Coulomb and harmonic potential

I am struggling over a problem and i could really use some help in this. So it's about finding phase shifts in a localized sphere of coulomb and harmonic potential. I tried solving the radial Schrodinger equation for both of them by using power series method, but still i am having problem...
8. ### Deriving Pith Ball Mass from Coulomb's Law: A Scientific Exploration

I actually found most of it out I'm just struggling with how to find the mass of the balls. I'm not sure how you would do that since could only derive two equations from the information given or are we assuming the mass is so small that it doesn't matter? Q = charge of one pith ball d =...
9. ### Propagation speed of Coulomb fields

Moderator's note: This thread is a spin-off of https://www.physicsforums.com/threads/what-are-the-most-important-open-questions-in-classical-physics.983671/ R. de Sangro, G. Finocchiaro, P. Patteri, M. Piccolo, G. Pizzella, "Measuring propagation speed of Coulomb fields", Eur. Phys. J. C 75...
10. ### How to know whether motion is simple harmonic motion or not?

I am reading "Coulomb and the evolution of physics and engineering in eighteenth-century France". There it is said in page 152 para 1 that "Coulomb found that within a very wide range, the torsion device oscillated in SHM". My questions are: (1) By just looking at the time period of the...
11. ### A Coulomb and Exchange Integrals

Summary: I'm looking for a table of Coulomb and exchange integrals for Lithium and beyond. I'm looking for a convenient table of Coulomb and exchange integrals for Lithium and beyond. I've looked everywhere and I find integrals for J,K 1s, 2s or 1s,2p for Helium. Does anyone know of a...
12. ### Question on Calculating Coulomb force in VECTOR FORM

The only thing tripping me up here is that the answer needs to be in vector form. If the question was asking for the scalar form, then I would just find the distance between the charges (plot the charges according to their vector coordinates, then use pythagorean theorem to find the distance...
13. ### B Coulomb Force: Is my understanding correct?

In a bound state like atom nucleus (except H-1), protons carry a positive charge so repel each other by the Coulomb force. This type of electromagnetic force, (also referred to as electrostatic repulsion) is an inverse-square force (has infinite range characteristics), so a proton added to a...
14. ### Relationship between coulomb energy and binding energy

which relationship exists between the coloumb energy and binding energy
15. ### B Coulomb force over Rindler horizon

Let's say a rocket carrying a positively charged balloon starts to accelerate with a constant proper acceleration at time t. After a long time another rocket carrying a positively charged balloon is launched. The crew of this rocket drives the rocket to a position right below the...
16. ### B Is the Coulomb Force Limited by the Pauli Exclusion Principle in Hydrogen Atoms?

Can charges collapse under coulomb attraction like charge-less matter does under gravity? In a way it's similar to asking about the lower limit of coulomb force if there is any. Also, does Pauli exclusion principle save the day just as in the case of gravity?
17. ### Calculating total Coulomb force vector ?

Homework Statement Consider a configuration consisting one +q charge ( upper right) and three −q charges, arranged in a square. Side lengths = d. Calculate the total F force vector acting on charge +q.Homework Equations Vector form of culomb’s force F=( kq1q2/r^2) rhat (rhat for unit...
18. ### Electric Field of a Non-Uniformly Charged Sphere | Homework Help

Homework Statement A solid isolated sphere with radius R has a non uniform charge which is given by ρ= Ar², with A a constant and r<R measured from the centre of the sphereHomework Equations (a) Show that the electric field outside the sphere is equal to E = (AR5)/(5ε0r²) (b) Show that the...
19. ### Rutherford scattering with Coulomb cutoff

Hello, I am reading a section in Jackson discussing classical Rutherford scattering, and he mentions incorporating a cutoff in the Coulomb interaction in order to model electric screening. I am trying to understand how he applies this, as described below. The set up is basically the classic...
20. ### Point Charges on a Polygon with another Charge in the Middle

Homework Statement Suppose we have a regular n-gon with identical charges at each vertex. What force would a charge ##Q## at the centre feel? What would the force on the charge ##Q## be if one of the charges at the vertices were removed? [/B]Homework Equations Principle of Superposition, the...
21. ### What is the minimum charge needed for a ball to jump in an electric field?

I don't really know how to fit what i want to this template, but i'll try. The thing is that i wonder if anyone can explain to me step-by-step what happened in this solution, because i don't really understand it. Homework Statement There are two balls. Upper one(mass m, charge Q) hung on a...
22. ### What is the initial charge of the second object in Coulombs?

Homework Statement Suppose an object has a charge of 1 C and gains #9.38 ✕ 10^18# electrons. When another object is brought in contact with the first object (after it gains the electrons), the resulting charge on the the second object is 0.9 C. What was the initial charge (in Coulombs)...
23. ### A Coulomb Klein Gordon: Where does e^(-iEt) come from?

Hi everyone, I've been reading about the Klein Gordon equation with the Coulomb Potential. The full solution can be found here: http://wiki.physics.fsu.edu/wiki/index.php/Klein-Gordon_equation#Klein-Gordon_equation_with_Coulomb_potential I'm confused near the beginning of this. I understand...
24. ### Hanging pith balls on a thread...charge, Fg, Fe and tension

Homework Statement Two pith balls each have a mass of 1.0g and equal charges. One pith ball is hung from an insulating thread. The other is fixed at a horizontal distance of 3.0cm from the first, The first hangs at an angle of 30.0° from the vertical. Find: a) the gravitational force on the...
25. ### EM fields of two opposite moving point charges

I wrote and solved this problem but am having serious doubts about the answer I obtained. Homework Statement Two point charges \pm q move along the z-axis with velocity \pm v. If they are at the origin when t=0, what is the electric field magnitude a distance r from the z-axis? Homework...
26. ### Calculate the total force on Q1

Homework Statement Q1<------>Q2<------>Q3 In the above figure, the distance between Q1 and Q2 is equal to the distance between Q2 and Q3. That distance is R=1.5 m. Q1= 2.24x10-6 C, Q2=+Q1 and Q3=-Q1. Calculate the total force on Q1. Give your answer with a positive number for a force...
27. ### How can each Coulomb of charge transfer energy

regards my question is how each coulomb of charge can lose (transfer ) energy when going from a to b when electrons are very slow the definition of potential difference: is how much each coulomb of the charge loses (transfer ) energy when going from a to b an example to clarify the question...
28. ### How to calculate the Coulomb barrier between a proton and a lithium nucleus

Homework Statement How to calculate the Coulomb barrier between a proton and a lithium nucleus. The variable is r (interaction radius). The known data is Z1, Z2, k (Coulomb constant), and e (elementary charge). Homework Equations The equation is UCoul = kZ1Z2e2/r The Attempt at a Solution I...
29. ### Coulomb force and charge equilibrium on the xy-plane

Homework Statement Two point charges q and 4q are located at r1 and r2, respectively, on the xy- plane. The magnitude Q and location R of a third charge to be places on the plane such that the total force on each of the three charges vanishes, are? first i plotted the problem on the xy...
30. ### Work, energy, power unit (coulombs)

Homework Statement For a positively-charged particle at the origin, and a negatively-charged particle lying to its right on the positive x-axis, the electrostatic force on the negative charge is attractive, and Coulomb's Law gives the magnitude of that force: F = k |Q1| |Q2| / x^2 k is...
31. ### I How does one find interaction radius for Coulomb barrier?

For a proton striking an atomic nucleus (in a Cockcroft-Walton accelerator, for example), the Coulomb barrier must be overcome. The calculation of the Coulomb barrier is U = k Z1Z2 e2 / r r is interaction radius. How can I find that? For a proton to enter the atomic nucleus what would it be?
32. G

### Electric Potential Energy - Final Velocity

Homework Statement Four protons (each with mass 1.7 10-27 kg and charge 1.6 10-19 C) are initially held at the corners of a square that is 7.1 10-9 m on a side. They are then released from rest. What is the speed of each proton when the protons are very far apart? (You may assume that the...
33. ### B Tidal effect in the balance of Coulomb and nuclear forces?

In a heavy nucleus, the balance of the Coulomb and nuclear forces is a delicate one. This can be seen in two cases: First, in oblong deformed nuclei, alpha particle emission is more likely to occur at the poles, where the Coulomb barrier is thinner, than at the waist. Second, heavy synthetic...
34. ### A QED propagator in Coulomb gauge

My aim is to derive the photon propagator in an Coulomb gauge following Pokorski's book method. In this book the photon propagator in Lorenz gauge was obtained as follows: 1. Lorenz gauge: ##\partial_{\mu}A^{\mu}=0## 2. It's proved that ##\delta_{\mu}A^{\mu}_T=0##, where...
35. ### A Photon propagator in Coulomb gauge

My aim is to derive the photon propagator in an Coulomb gauge following Pokorski's book method. In this book the photon propagator in Lorenz gauge was obtained as follows: Lorenz gauge: ##\partial_{\mu}A^{\mu}=0## It's proved that ##\delta_{\mu}A^{\mu}_T=0##, where...
36. ### B Account for Coulomb repulsion in nuclear fission energy?

Hi, I have learned that, in a nuclear fission or an alpha decay, the available energy released is the difference of masses between the initial nuclide (+ eventually some other initial particles) and the output particles, times c^2 (as E = mc^2). I'm fine with that. But I wonder : what about...
37. ### Paradoxes of the Coulomb friction

From Painleve we know that Coulomb's law of friction being applied to rigid bodies systems may produce contradictions. Painleve constructed several examples of such contradictions, so called Painleve's paradoxes, see [Painleve P. Leçons sur le frottement. P.: Hermann, 1895]. Those examples...

45. ### How Does the Charge Q Affect Forces Between Q1 and Q2?

Homework Statement A positive point charge Q_1 (4.0 µC) and a negative point charge Q_2 are placed near each other. When a negative charge Q is placed in the middle between the two point charges, the magnitude of the resultant forces on Q_1 and Q_2 doubles. What is the charge of Q? (answer...
46. ### B Quantum superposition of Coulomb potential

As I understand Coulomb potential associated with charged particle is described classically. My question is if there is a way how to describe Coulomb potential of charged particle that is in quantum superposition of being "here" and "there"? My motivation for question is that I am trying to...
47. ### Ampere & Coulomb: Discovering Electrons in 1800's?

ok, so i am taking an auto electrical class this semester and i can not continue reading the book/doing the homework until i understand this..my question is this: if andré marie ampére (1775-1836) discovered the electron flow, how the hell did he do it back then? how did they discover atoms and...
48. P

### B Can you gurus help me understand in a qualitative way the nature of the Coulomb barrier

Can you gurus help me understand in a qualitative way the nature of the Coulomb barrier as it applies to alpha decay? I can intuitively appreciate the Coulomb barrier as it applies to anincoming charged particle, but resources I have been reading apply the same term to the barrier felt by...
49. ### I Fourier transform of Coulomb potential

Dear all, In my quantum mechanics book it is stated that the Fourier transform of the Coulomb potential $$\frac{e^2}{4\pi\epsilon_0 r}$$ results in $$\frac{e^2}{\epsilon_0 q^2}$$ Where ##r## is the distance between the electrons and ##q## is the difference in wave vectors. What confuses me...
50. ### Rayleigh–Ritz method - Yukawa coulomb potential

Hello everyone Homework Statement I have been given the testfunction \phi(\alpha, r)=\sqrt{(\frac{\alpha^3}{\pi})}exp(-\alpha r) , and the potential V(r,\theta, \phi)=V(r)=-\frac{e^2}{r}exp(\frac{-r}{a}) Given that I have to write down the hamiltonian (in spherical coordinates I assume), and...