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. A

    Hooke's law and the Coulomb force

    Homework Statement An unstrained horizontal spring has a length of 0.32 m and a spring constant of 220 N/m. Two small charged objects are attached to this spring, one at each end. the charges on the objects have equal magnitudes. Because of these charges, the spring stretches 0.020 m, relative...
  2. Roodles01

    Total energy of Coulomb model of Hydrogen atom

    Homework Statement Hi, my question is regardng a Coulomb model of an H atom specified with Hamiltonian operator, Hhat, by spherical coordinates of energy eigenfunction ψ2,1,-1 (r,θ, ∅) =(1/ 64∏a02)1/2 r/a0 e-r/2a0 sinθ e-iθ Principal quantum numer n = 2 orbital an mom l = 1 magnetic...
  3. T

    What is the net force on the third spider (S3)?

    Homework Statement The sides of the triangular web have a length of a = 0.74 m, as depicted in the figure. Two of the spiders (S1 and S3) have +6.6 µC charge, while the other (S2) has −6.6 µC charge. a.) What are the magnitude and direction of the net force on the third spider (S3)? I...
  4. B

    Modified Coulomb model for hydrogen, minimising error

    Homework Statement The ground energy can be approximated as E_{1}^{(1)}\approx-\frac{4b^2}{a_0^2}E_R Find the largest value of b that would be consistent with the ground-state energy of a hydrogen atom that agrees with the predictions of the Coulomb model to one part in a thousand...
  5. Y

    Question on Coulomb and Lorenz Gauge

    This is Problem 10.6 in page 422 of "Introduction to Electrodynamics" Edition 2 by David Griffiths. The question is: Which of the potentials in the following is in the Coulomb gauge? Which is in Lorenz Gauge?( Notice that these gauges are not mutually exclusive.) This is what the solution...
  6. T

    Dimensional Units for Coulomb in SI

    Does anyone know of a dimensional formula for the Coulomb in SI that does not involve amperes as in A*s? I am looking at some equations and the dimensional analysis is leaving me with C (Coulomb unit charge) and left over m, kg, s to various powers. Just curious if anyone has come across some...
  7. T

    Coulomb Gauge invariance, properties of Lambda

    Homework Statement A gauge transformation is defined so as to leave the fields invariant. The gauge transformations are such that \vec{A}=\vec{A'}+\nabla\Lambda and \Phi=\Phi'-\frac{\partial\Lambda}{\partial t}. Consider the Coulomb Gauge \nabla\cdot\vec{A}=0. Find out what properties the...
  8. Roodles01

    Confusion about Coulomb's Law and 3 Point Charges

    Homework Statement 2 questions regarding the answer I have been given for this problem. Attachments are the problem & relevant worked answer I disagree with. Problem Three charges are arranged in the xy-plane as shown in attachment. A charge Q is at the point A with (x, y) coordinates...
  9. tsuwal

    Coulomb law dedution from Maxwell equations

    I'm starting my study in eletromagnetism and I would like to know how do you deduce the eletric field produced by a single particle of charge q placed in the origin. The magnetic field is constant so by Maxwell equations, the rotacional is 0 and the divergence is constant. Is this enough to...
  10. P

    Very Hard Integral (from int Coulomb) with -3/2 power + others

    Homework Statement I am trying to directly calculate the electric field (using Coulomb) at some arbitrary point P(0,0,z). The charge is evenly distributed over the surface of a sphere (radius R, charge density σ). Here I use θ for the polar angle and p for the azimuthal angle. I will leave...
  11. E

    Two reacting nuclei, maximum distance to overcome the coulomb barrier

    Basically I'm trying to find out how to find the maximum distance between two deuterium nuclei in order to overcome the coulomb barrier, causing them to fuse. Thanks
  12. M

    Coulomb Energy in the KI Molecule: Solving for Separation Distance

    The ionization of potassium is 4.34 eV; the electron affinity of iodine is 3.06 eV. At what separation distance will the KI molecule gain enough Coulomb energy to overcome the energy needed to form the K^+ and I^- ions? I'm looking at the solution to this problem and I'm not understanding how...
  13. B

    Very hard Coulomb Force with two charges

    I'm new to forums and after I typed all this out and tried to submit, it cleared everything. I really need to get this problem finished tonight. 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...
  14. S

    Help: From Ampere to Coulomb in SI units

    Hello, Could someone help me finish this train of thought? This is how we think in SI units: First, just because we like the value of 1 Ampere as it is now, we choose the force between two parallel conductors to be exactly 2×10^{-7}N= const ×\frac{1A×1A}{1m} Then, purely as choice, we decide...
  15. xaratustra

    Understanding Coulomb's Law: Particle Acceleration and Energy Exchange Explained

    It is known from the Coulomb's law (F = q E) that if an electric field is applied on a charge, it will accelerate it, i.e. the position of the particle changes macroscopically. But why mechanical displacement? why not a change in particles internal energy, say for example excitation of an...
  16. C

    Coulomb barrier and proton evaporation

    Why is it that neutrons evaporate from nuclei more easily than protons do? Intuitively, since protons are electrostatically repelled (in addition to whatever nuclear forces they have in common with neutrons), one would expect protons to be ejected more readily than neutrons. (Maybe this is...
  17. P

    When should I consider the sign of charges when applying Coulomb's Law?

    I am studying Physics Vol2 by halliday, resnick and krane. I was attempting the coloumb force exercises..If we put one charge negative and other positive in the formula..then the force comes out to be negative but the instructor manual for the book ignores the negative charge, and take it as...
  18. M

    Coulomb potential in Kohn-Sham DFT

    In Kohn-Sham DFT, the Coulomb potential, which is a component of the Kohn-Sham potential, is given by: v_H(\mathbf{r}) = \int \frac{\rho(\mathbf{r'})}{|\mathbf{r}-\mathbf{r'}|}d\mathbf{r'} where \rho(\mathbf{r'}) is the electron density. For molecular systems with exponential densities...
  19. Z

    Electron magnetic replusion compared to coulomb attraction

    I know that the electron has an electric charge of 1.6x10^-19C and a magnetic moment of 9.3x10-24J/T. If you placed two electrons 1 angstrom apart in such a way as their north poles are pointing at each other, the coulomb force would attract them and the magnetic force would repel them. Which...
  20. D

    Solving Coulomb Barrier Penetrability with a Confusing Formula

    Homework Statement There isn't an exact problem I'm struggling with, it's one small part of a larger problem, which involves finding the probability protons will penetrate the Coulomb barrier. I'm trying to understand an example in my notes, and the bit that confuses me is attached as an...
  21. T

    Understanding Coulomb Force in Plasmas

    This may be a pretty dumb question. How is it possible for ions and electrons to coexist in plasma state. Shouldn't be there Coulomb force between them so that they would be bound together and become atoms?
  22. A

    Gauge transformations and the coulomb gauge

    My book has introduced the idea of gauge invariance in terms of classical electrodynamics (attached file). However, I am not sure I completely understand how it works. On the one hand they use a lot of time on specifying how you can add to the vector potential the gradient of any scalar, whilst...
  23. F

    Electrostatics balancing gravitational, coulomb forces and tension

    Homework Statement Hi, I'm on the first part of this question and I've got to the end but I have an extra factor of two which I can't seem to explain! Any insight would be much appreciated, thank you! Homework Equations The Attempt at a Solution I resolved the forces around one ball and came...
  24. Roodles01

    Calculating Coulombic Forces on a Particle: A Symmetrical Three-Particle System

    Homework Statement I have a simple question about forces on separated particles, but still need a bit of help. I have put down what I can: 3 particles; A on y-axis @ √3, charge "q" B & C each on x-axis, symmetrical about origin, separated by 2a, both charge "q". Find magnitude & direction of...
  25. W

    Monte-Carlo simulation Coulomb potential scattering

    Dear all, I just started learning about the Monte-Carlo methods of simulating particle interactions. I would like to ask a question about simulating potential scattering. In particular I think that the simulating scattering by Coulomb potential, and writing a corresponding MC test program might...
  26. J

    Relativistic Coulomb potential - how to understand the equation

    Hi, I need a formulation of the equation for Coulomb's potential. It needs to be an integral that applies to densities (so no delta functions). (I think the relevant densities are charge densities?) Also, it needs to be relativistic. So far I have: ? = \int\frac{ρ(r'...
  27. AGNuke

    Charge moving in elliptical orbit under Coulomb field.

    Under the influence of the coulomb field of charge +Q, a charge −q is moving around it in an elliptical orbit. Find out the correct statement(s). (A) The angular momentum of the charge −q is constant (B) The linear momentum of the charge −q is constant (C) The angular velocity of the charge...
  28. Roodles01

    Finding Charge at a Specific Point Using Coulomb's Law

    I am working on the following. A point charge of √3Q is at point (3a, a, 2a) Find charge at (2a, 2a, 3a) I'm using Coulomb's Law E(r) = q / 4∏ε0 (r-r0)3 ([B]lr-r0l[B] & can get through most of it, but looking at my book I can't see why the last step occurs. See attachment. I can find r-ro &...
  29. A

    Coulomb Energy Unit Conversion: MeV

    I'm having some difficulty resolving the units (unit conversions will be my great un-doing) for calculation of the Coulomb energy between nuclei. Given that \Delta E = \frac{3e^{2}}{5r} (2Z-1) with the value for r in fermis (~10^-13cm), the elementary charge e in coulombs, and Z is...
  30. J

    Coulomb force if dielectric is placed in between them

    Homework Statement two charges q1 and q2 are palced at a distance r. A slab of thickness t is placed between the two cahrges having dielectic constant k. Find coulomb force between the charges. Homework Equations Well F = q1q2 / 4∏ε°k - this would have been the force if the slab was...
  31. J

    Coulomb law for moving charges

    I am trying to workout the drift of a charged particle from another particle using coulomb law. but the problem is the further the particles move, the less the force between them, so how can I work out the drift in such case? We know that the force between two charged particles is: F = (k Q1...
  32. K

    Why did Coulomb choose 1.6x10^-19 for the charge of an electron?

    Does anyone know why Coulomb chose 1.6x10^-19 for the charge of an electron? (or why he chose 6.25x10^18 electrons for 1 coulomb)
  33. N

    Joules per Coulomb and the Volt

    Hey, A coulomb is the amount of charge that passes a point through a wire carrying one ampere for one second. Voltage is a measure of electrical potential energy in units of volts or joules per coulomb (energy/charge). Then 1 volt means 1 joule per coulomb; 2 volts mean 2 joules per coulomb...
  34. O

    Cross section of coulomb sacttering vs Rutherford

    differential cross section of coulomb scattering can be expressed as a form factor times Rutherford one, we model the charge we used spherically symmetric charge density, if we replace this point charge with other distribution like Gaussian , what is the difference between these two models, is...
  35. B

    Finding Q values of decays and finding distance where Coulomb Barrier = Q value

    Homework Statement 224Ra --> 220Rn + \alpha 224Ra --> 212Pb + 12C 224Ra --> 210Pb + 14C Calculate the Q-Values (in MeV) for these decays given their atomic mass excesses (in MeV) are 88225Ra = 18.818 86220Rn = 10.604 82212Pb = -7.557 \alpha = 2.425 82210Pb = -14.743...
  36. maverick_starstrider

    Instantaneous communication, Aharanov-Bohm and the Coulomb Gauge

    I'm just curious, in the Coulomb gauge changes made locally to the scalar and vector potential fields are propagated instantaneously, classically we wave off this problem since the potentials aren't directly observable... except they are in Aharanov-Bohm. Presumably there's something that saves...
  37. R

    Coulomb Gauge and Gauge Transformation

    I understand the conceptual meaning of gauge transformation which "can be broadly defined as any formal, systematic transformation of the potentials that leaves the fields invariant". I understand for example the U(1) and S(3) gauge symmetry in Gauge Theory. But what is this got to do with...
  38. Gamma

    Tedious Algebra- Is it needed? - Coulomb Force

    Hello, A typical problem assigned to students is where there are two charges on the x-axis and find the location of a third charge so that the net force on it is zero or some other force value given. I am wondering what is the idea behind this problem? It can get really complicated when...
  39. tom.stoer

    QED in Coulomb Gauge: Deriving the Coulomb Force and Questions

    I presented a way to derive Coulomb force via the canonical mechanism. One uses Coulomb gauge \partial_i A^i = 0 derives \Delta A_0 = -4\pi\,\rho which can be inverted formally A_0 = -4\pi\,\Delta^{-1}\,\rho and calculates the interaction term in the Hamiltonian density...
  40. D

    Quantization of vector field in the Coulomb gauge

    I have a technical question and at the time being I can't ask it to a professor. So, I'm here: If I try to quantize the vector field in the Coulomb gauge (radiation gauge) A_0(x)=0,\quad \vec\nabla\cdot\vec A=0. by imposing the equal-time commutation relation...
  41. J

    Coulomb Integral for Diatomic Hydrogen Ion

    Homework Statement What does the non-negativity of the Coulomb Integral for H2+ suggest about the relative strengths of the attractive electron-proton force and the repulsive proton-proton forces? Homework Equations N/A The Attempt at a Solution I want to say that it means the...
  42. Z

    Total Excess Charge using a Coulomb Balance

    Homework Statement If conducting a Coulomb Balance experiment, and a question asks to estimate the total excess charge on a sphere with a conducting surface charged to 2,000,000V potential. Is there a specific equation I should be using to estimate this? Thank you. P.S. why are...
  43. C

    Overcoming the Coulomb Barrier: Energy Requirements

    How much energy particles must have in order to overcome the Coulomb Barrier? Or the correct way to ask this is how much temperature is required for this?
  44. A

    Proton Collision and Coulomb Barrier

    Homework Statement What temperature would be required for two protons to collide if quantum mechanical tunneling is neglected? Assume that nuclei having velocities ten times the root mean square (rms) value for the Maxwell-Boltzmann distribution can overcome the Coulomb barrier (which you can...
  45. Q

    What is Coulomb potential and energy?

    is it just potential and potential energy? but if so, why is it given as V(r) = - Ze2 / 4πεr ? and E = Z2e2 / 4πεr i am having trouble understanding how come for potential V, Q = Ze2 while for E, Q2 = Z2e2 thanks!
  46. F

    Is there any significant difference between Gravitational and Coulomb Force (/Δ PE)?

    The definition of Δ (difference,drop of) Electrostatic Potential Energy (D E-PE) says it 'is the work done on a unit charge (e) to bring it from r to r1 (against the force) with constant (without acceleration) velocity and extremely low absolute value of velocity (quasistatic, vanishingly...
  47. K

    Calculating Coulomb friction load torque

    Hi How can I calculate the Coulomb friction load torque of a rolling spear on a surface with a coulomb friction coefficient of 0.1? Other details: Mass: 1Kg Radius: 0.1m Thanks in advance
  48. J

    Units of Coulomb, trouble understanding the question

    Homework Statement Two charges, q1 = 4.9 e C and q2 = -3.6 e C are located 105nm apart, what is the size of the force between the two charges?Homework Equations F=kqq/r^2 The Attempt at a Solution I did it according to the formula and I got the answer wrong, so I checked it using an online...
  49. B

    Coulomb Law and Vectors - How do you find a scalar answer from the vector form?

    Coulomb Law and Vectors - How do you find a scalar answer from the vector form?? Two small metal spheres carry equal charges q. They are located at positions r1 = (1,1,0) nm and r2 = (0,0,0) nm and feel a repulsive force of magnitude (mod) F = 0.05 N How much charge is on each sphere...
  50. Y

    Question about retarded scalar potential and Coulomb Gauge.

    This is exact copy from Griffiths Introduction to Electrodynamics 3rd edition page 421. This is regarding to information travel in space. In time varying situation, E depend not only on V, but on A also.
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