What is Coulomb: Definition and 232 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. AwesomeTrains

    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...
  2. J

    Perturbation first order hydrogen - Coulomb model

    Homework Statement Assume that there is a deviation from Coulomb’s law at very small distances, the Coulomb potential energy between an electron and proton is given by V_{mod}(r)=\begin{cases} -\frac{q^{2}}{4\pi\varepsilon_{0}}\frac{b}{r^{2}} & 0<r\leq b\\...
  3. S

    Magnitude of the E-Field at the center of curvature

    Homework Statement A circular rod has a radius of curvature R = 8.11 cm, and a uniformly distributed positive charge Q = 6.25 pC and subtends an angle theta = 2.40 rad. What is the magnitude of the electric field that Q produces at the center of curvature? Homework Equations E = kQ/r^2 6.25 pC...
  4. S

    Distance from potential difference

    Homework Statement A metal sphere of radius 15 cm has a net charge of 4.2x10^-8C. At what distance from the sphere's surface has the electric potential decreased by 500V? Homework Equations V = kQ/r The Attempt at a Solution \Delta V\quad =\quad \frac { kQ }{ r } \\ \\ r\quad =\quad \frac {...
  5. S

    Finding velocity given potentials of two parallel plates

    Homework Statement A charged particle (either an electron or a proton) is moving rightward between two parallel charged plates separated by distance d=2.87mm. The plate potentials are V1=-75.8V and V2=-49V. The particle is slowing from an initial speed of 90.0 km/s at the left plate. What is...
  6. S

    Electric field lines from a metal shell and sphere

    Homework Statement A metal sphere of charge +6μC is surrounded by a metal shell of net charge +6μC. Which of the following diagrams represents the electric field lines of the system? Homework EquationsThe Attempt at a Solution The correct answer provided by my teacher is a figure with 12...
  7. I

    Binding energy, Coulomb energy

    Homework Statement a) Calculate the difference in binding energy between the mirror nuclide ##^{15}O## and ##^{15}N##. b) Calculate the radius of both nuclide’s assuming the difference in binding energy exclusively depends on difference in Coulomb energy. Homework Equations Mean nuclear radius...
  8. P

    How Many coulombs pass through each resistor in a circuit?

    Homework Statement My question relating to physics and electric circuits, is "If a circuit consists of a 12 volt battery and two ohm resistors connected in series, then how many Coulombs pass through each resistor in a second". Thank you all so very much. Homework Equations V=IR The Attempt...
  9. Sam19KY

    What is the Definition of Coulomb in Particle Physics and Electrodynamics?

    When we say "1 coulomb is equal to charge on 6.24 x 10^18 electrons" does "charge" mean elementary charge or simply -1 ?
  10. Sam19KY

    Is this how a coulomb is defined ?

    Charge on one electron (elementary charge) = 1.60217662 × 10-19 coulombs. Charge on 6.241509745 x 10^18 electrons is equal to 1 coulomb. So the two values above are multiplied to give one coulomb of charge ?
  11. ShayanJ

    Coulomb potential as an operator

    I want to calculate the commutator ##{\Large [p_i,\frac{x_j}{r}]}## but I have no idea how I should work with the operator ##{\Large\frac{x_j}{r} }##. Is it ## x_j \frac 1 r ## or ## \frac 1 r x_j ##? Or these two are equal? How can I calculate ##{\Large [p_i,\frac 1 r]}##? Thanks
  12. ShayanJ

    SO(4) symmetry in the Coulomb potential

    In chapter 4 of "Modern Quantum Mechanics" by Sakurai, in the section where the SO(4) symmetry in Coulomb potential is discussed, the following commutation relations are given: ## [L_i,L_j]=i\hbar \varepsilon_{ijk} L_k## ## [M_i,L_j]=i\hbar \varepsilon_{ijk}M_k## ## [M_i,M_j]=-i\hbar...
  13. A

    At what point along the x axis is the electric field zero?

    Hello, I've been trying to answering this question but my answer is always wrong. Two point charges, -9.10 μC and 21.29 μC, are placed at x = 0 cm and x = 8.00 cm, respectively. (a) At what point along the x-axis is the electric field zero? What i did: i figured that the point should be on the...
  14. K

    Coulomb gauge derivation (static field)

    Hi, I am a little confused of derivation of Coulomb Gauage. (2) First, prime notation is adopted to describe the magnetic field density source current. Non-prime notation is for position that we are specifically interested in (ex. the position magnetic force acts on)...
  15. R

    (Simple Electromagnetics) A charge placed between 2 charges

    Homework Statement A charge (q) is placed in-between two other equal charges named Q. Q-----q-----Q a) If both Q's are positive, is charge q in equilibrium? If yes, is it a stable or unstable equilibrium? b) What about if one Q is negative while the other is...
  16. shio

    Why do we need to square the separation in Coulomb's experiment?

    Coulomb experiment torsion balance. I know that electrical force is inversely to the square of the separation r ...My question is why we take r square? why we need square? And another question, why Q1Q2(multiplication of charges) is proportional to electrical force? (why we need to multiply...
  17. tomdodd4598

    Plotting the Probability Density of the Coulomb Wave Function

    Hey there - I think I have an issue with my 3D density plots of the probability density of the Coulomb wave function. The reason I think something is going wrong is because my plots of |ψ(n=2, l=1, m=-1)|² and |ψ(2, 1, 1)|² are identical, while I would expect them to have the same shape but be...
  18. tomdodd4598

    Normalised Radial Coulomb Wave Function

    Hey there, I used Mathematica to find the (non-normalised) wave function of an electron in the vicinity of a Hydrogen nucleus, and converted the answer from one involving Whittaker functions to one involving generalised Laguerre polynomials. My result is shown below: This agrees with the...
  19. azizlwl

    Calculating Coulomb Force on a Point Charge in a Square Distribution

    Homework Statement Find the force on a point of charge of 30μC at (0,0,5)m due to a 4m square int he z=0 plane between x=±2m and y=±2m with a total of 500μC, distributed uniformly. Homework EquationsThe Attempt at a Solution R=-x,-y,+5z dQ=ρdydx=500/4 dydx dE=dQ(5az) / (4πε0((x2+y2+25)3/2 ) x...
  20. pawlist

    Find Mag of Charges for 50 cm, 0.2g & 37 Degrees

    Homework Statement I need to find the magbitude of charges Lenght of string - 50 cm mass of balls - 0.2 grams theeta - 37 degrees Homework Equations K-8.99x10^9 [/B]The Attempt at a Solution I found that half the distance between the balls is 15.9 cm but i don't know how to continue[/B]
  21. Ankhen

    Converting Coulombs to Joules Without Voltage

    Hi Is it possible to convert coulomb to joule without knowing volt?
  22. snowjoe

    Why is the basic charge not equal to the reciprocal of a Coulomb?

    why isn't the number of e or p making a Coulomb the same as the reciprocal of the 'basic' charge if the basic charge is defined as a fraction of a Coulomb? basic charge = 1.6 x e-19C, but number of p or e constituting a C is 6.25 x e18
  23. L

    Coulomb triple integral for a sphere

    Homework Statement Find the electric field of a sphere of radius R and charge Q outside sphere. Use only a Coulomb integral to do this. Homework Equations I know that I have to use a triple integral to find the E-field. I am just unsure of my whole setup really. The Attempt at a Solution...
  24. Hardik Batra

    What is the unit value of coulomb constant(k)?

    What is the unit value of coulomb constant(k)? I just want to know the CGS unit value of k. In my book it is said the CGS unit value of k is 1. By i don't know how it come.?
  25. S

    How did Coulomb charge his spheres to verify Coulomb's law?

    We are doing an experiment to verify coulomb's law, and we are currently using a stable voltage source. However, we were assigned to do it using static electricity, and we were wondering how to establish inverse r^2 dependence if the amount of the charge on the ball isn't the same every time we...
  26. S

    Calculating Distance Between Charges Using Coulomb's Law

    Homework Statement What is the distance between two charges of -5.00 C each if the force of electrostatic repulsion acting on them is 5.00 x 10^3 N?[/B]Homework Equations Is this rearrange formula correct? r^2=k(q1q2) / F[/B] The Attempt at a Solution 6704m
  27. F

    Natural frequency of 3 coulomb force bound particles in EF

    Homework Statement I was given a task to model (using Matlab) 3 identical particles in external field and find spectra of lowest system energy states using gradient descend method for each particle in the system. I did a run of 500 random generated coordinates and found this distribution...
  28. chikou24i

    Prove e(charge of proton)=1.6E-19 | Mev.fm

    How to prove that e(the charge of proton)=1.6E-19 Mev.fm
  29. A

    Probability to overcome Coulomb repulsion

    Homework Statement The temperature in the interior of the Sun is about 1.5E7 K. Consider one of the reactions in the thermonulcear synthesis chain: p+p->H_2 + e^+ neutrino. In order for this reaction to occur two protons have to be at the distance of about 1 fm (10E-15 m). Estimate the...
  30. DiracPool

    Coulomb potential in hydrogen atom nomenclature

    I'm seeing a version of the potential as -Ze^2/4πεr. My question is what exactly does the Ze^2 refer to? I think the e^2 is supposed to represent the proton and the neutron, and the Z is supposed to represent the number of protons, but I'm not sure how to read it. Does e refer to the charge...
  31. T

    Resources for variational principle to solve coulomb problem in D dimension

    Hi, i have been struggling to find some good resources on variational principle , I have got an instructor in advanced quantum course who just have one rule for teaching students- "dig the Internet and I don't teach you anything".. So I digged a lot and came up with a lot reading but I need...
  32. A

    Spring with Coulomb Friction

    Homework Statement A mass m is attached to a spring with spring constant k. There is a coefficient of static friction, us The coefficient of kinetic friction is uk Suppose you pull the mass to the right and release it from rest. You find there is a limiting value of x = A0 > 0 below which the...
  33. Q

    Kinetic Energy Gain due to Coulomb Force

    Homework Statement Hi guys! I have a problem pertaining to the kinetic energy gained by a point charge from interacting with a another point charge. Here's the problem: A point charge of mass m1 and charge q is placed near another point charge with mass m2 and charge Q. Both charges are of...
  34. Greg Bernhardt

    What Is the Coulomb Gauge in Electromagnetic Theory?

    Definition/Summary A particular choice of "gauge fields" in which the vector potential has no divergence. Equations \nabla\cdot\vec A=0 Extended explanation As explained elsewhere, one introduces "gauge fields" in order to identically solve two of the four Maxwell equations...
  35. R

    Coulomb interaction not affected by presence of other charges

    One of the observation noted in connection with coulomb interaction is that, it is not affected by the presence of other charges. Why? Thanks.
  36. A

    Coulomb term in Potential of ions in a Penning Trap,Green's Function

    How do you write out the potential of an ion in a Penning trap? Specifically, how does the inter-ionic Coulomb interaction come to be written as a Green's function? I found it here : http://journals.aps.org/rmp/pdf/10.1103/RevModPhys.71.87 They do say something about interactions with image...
  37. C

    Charge vs Coulomb - A paradox?

    Hi I'm wondering: The symbol of charge is Q but the SI unit of charge is coulumb which is the Charge of approximately 6.241×1018 electrons. But charge is not itself defined, only in terms of Coulomb, and coulomb is defined in termes of Charge. Its SI definition of Coulomb is the charge...
  38. Entanglement

    The original definitions of Ohm, ampere, volt and coulomb

    What's the original definition of Ohm, ampere, volt and coulomb, And which unit was defined according to the other ??!
  39. Y

    Evaluating the Coulomb Integral for a two-electron atom

    Homework Statement Evaluate the so-called Direct (or Coulomb) Integral, C, which occurs in the theory of the 2-electron atom. C=\int\int d\vec{r}_1d\vec{r}_2\left|\phi_a(1)\right|^2\left|\phi_b(2)\right|^2 \frac{e^2}{\left|\vec{r}_1-\vec{r}_2\right|} You may assume that both...
  40. P

    Calculate Coulomb: Help Solving Homework Problem

    Homework Statement The engine delivers 12 kW. Per second it can shift the m = 800 kg car over a vertical distance of 1.5 m. Find the current delivered by the batteries. Homework Equations P = U * I I = P/U = 12 000 W / 168 V = 71.4 A The Attempt at a Solution My Problem is...
  41. P

    Two-orbital system w/ tight-binding and Coulomb interaction

    We have a system of two orbitals 'a' and 'b'. The Hamiltonian is given as: $$H=\sum_{\sigma=\uparrow,\downarrow}(\epsilon_a A_\sigma^\dagger A_\sigma+\epsilon_b B_\sigma^\dagger B_\sigma) -t\sum_{\sigma=\uparrow,\downarrow}(A_\sigma^\dagger B_\sigma+B_\sigma^\dagger A_\sigma)+U...
  42. S

    Understanding Coulomb's Law for Electric Fields and Forces

    Homework Statement You have two charges, q1= -15uC and q2= 3uC, separated by a distance d= 3m. We want to calculate the electric field, E, at a location x relative to charge q2 located on a line connecting the two charges. Note that x could be anywhere on that line. Also need to calculate the...
  43. ShayanJ

    One dimensional Coulomb potential

    Consider the potential below: V(x)=\left\{ \begin{array}{cc} -\frac{e^2}{4\pi\varepsilon_0 x} &x>0 \\ \infty &x\leq 0 \end{array} \right. The time independent Schrodinger equation becomes: \frac{d^2X}{dx^2}=-\frac{2m}{\hbar^2} (E+\frac{e^2}{4\pi\varepsilon_0 x})X I want to find the ground...
  44. P

    Would modeling collisions using Coulomb forces be useful?

    Hi, I am trying to decide on a topic for my senior project, and my professor and I fleetingly discussed my idea of writing a program that models collisions of macroscopic objects using the mutual repulsive forces of their valence electrons rather than standard conservation laws. My question is...
  45. O

    Satisfying Coulomb Gauge: What are the Conditions for Vector Potential?

    Homework Statement We study the free electromagnetic field in a charge and current free cubic box with with edge length L and volume V. The vector potential in such a system is given via Fourier series: Homework Equations \vec{A}(\vec{r}, t) = \sum\limits_{k} \vec{A}_k(t) e^{i...
  46. M

    Coulomb force and the self electric field

    The well-known connection between the electric field and Coulomb's law is that The magnitude of the electic field at distance r from a point-charge Q is E=Q/r^2The definition of E is that the force exerted the field on a point-charge q is F=qE. These two equalities yield the F=qQ/r^2...
  47. B

    Coulomb Law: What Does k Mean & Why Is 4π Used?

    What k mean in coulomb law? it's 1/(4π*ε) but why is in this form? 4π it's related to the shape of an atom?
  48. A

    Numerically finding Coulomb gap

    Hello, I'm new in the realm of numerical analysis. I need to find the local probability density of energy P(E) of a single electron on site i from a self-consistent equation for the energy (mean field equation of energy)...
  49. D

    What came first, the coulomb or the amphere?

    I'm struggling to understand why 'amps' is a base unit. An amp is defined as one coulomb per second, correct? Then surely it isn't a base unit! It clearly relies on the coulomb. Like, if the coulomb didnt exist, or the amp was discovered before the coulomb was discovered, what would the amp be...
  50. S

    Exact modeling of coulomb stick-slip-friction using LCP

    Model I have a simple model. Say a 1DOF-Model like a box on a table pulled with a spring, which follows a given path. The friction between box (The position is y) and the table should be modeled with the coulomb-friction model. Like F_N\mu\geq F_T \rightarrow \dot{y}=0 F_N\mu<F_T...
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