# What is Coulomb law: Definition and 23 Discussions

Coulomb's law, or Coulomb's inverse-square law, is an experimental law of physics that quantifies the amount of force between two stationary, electrically charged particles. The electric force between charged bodies at rest is conventionally called electrostatic force or Coulomb force. The law was first discovered in 1785 by French physicist Charles-Augustin de Coulomb, hence the name. Coulomb's law was essential to the development of the theory of electromagnetism, maybe even its starting point, as it made it possible to discuss the quantity of electric charge in a meaningful way.The law states that the magnitude of the electrostatic force of attraction or repulsion between two point charges is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance between them,

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{\displaystyle |F|=k_{\text{e}}{\frac {|q_{1}q_{2}|}{r^{2}}}}
Here, ke is Coulomb's constant (ke ≈ 8.988×109 N⋅m2⋅C−2), q1 and q2 are the signed magnitudes of the charges, and the scalar r is the distance between the charges.
The force is along the straight line joining the two charges. If the charges have the same sign, the electrostatic force between them is repulsive; if they have different signs, the force between them is attractive.
Being an inverse-square law, the law is analogous to Isaac Newton's inverse-square law of universal gravitation, but gravitational forces are always attractive, while electrostatic forces can be attractive or repulsive. Coulomb's law can be used to derive Gauss's law, and vice versa. In the case of a single stationary point charge, the two laws are equivalent, expressing the same physical law in different ways. The law has been tested extensively, and observations have upheld the law on the scale from 10−16 m to 108 m.

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1. ### 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
2. ### I How is Coulomb's Law compatible with quantum physics?

In classical physics, we treat an electron as a point charge with a Coulomb potential ## V = \frac{q}{4\pi\epsilon_o r}##. However, in quantum mechanics, we treat it as an electron cloud. In this situation, how shall we describe the Coulomb potential? Shall we treat the electron as a charge...
3. ### Electric Flux through a circle

Hi! My main problem is that I don't understand what the problem is telling me. What does it mean that the surface is a flast disc bounded by the circle? Is the Gauss surface the disc? Does that mean that inside the circle in the figure, there is a disc? Can you give me some guidance on how to...
4. ### Force of one distribution of charge on another

Homework Statement I need help on solving this exercise : We have a ring of radius = ##a## uniformly charged (total charge = ##Q##) and on its axis a segment ##OA## (length = ##a## also) of uniformly distributed positive electric charges with the charge density ##\lambda'## and of total charge...
5. ### Problem in electrostatics: E-field near 2 point charges

Homework Statement Refer the image. Homework Equations kq1q2/r^2 = F Potential energy = kq1q1/r The Attempt at a Solution Obviously since both charges are unequal in magnitude option a is incorrect. Calculating field at large distance r, E = kq1/r^2 - kq2/r^2 = kq2/r^2 Also potential energy...
6. ### How do you calculate voltage from Coulomb’s equation?

I know that the equation F = CQ1Q2/r^2 can be rearranged to give electric field measured in volts per meter and then arearranged to get voltage but I don’t thing the answers I get are correct. I once got 10^9 volts between 2 coulombs 2 meters apart? I am really confused please help.
7. ### 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...
8. ### Coulomb's Law Grade 12 Question -- Net Electric Field affecting a Charge

Homework Statement Examine the charge distribution shown. b) What is the net electric field acting on charge 1? Homework Equations I used the equation E= (kq1/r^2) + (kq2/r^2) The Attempt at a Solution I subbed 9.0 x 10^9 in for k, 3.0 x 10^-5 for both q1 and q2, and 2m for r. My final answer...
9. ### Electric field magnitude between two charged disks problem

Homework Statement Consider two thin disks, of negligible thickness, of radius R oriented perpendicular to the x axis such that the x axis runs through the center of each disk. (Figure 1) The disk centered at x=0 has positive charge density η, and the disk centered at x=a has negative charge...
10. ### 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...
11. G

### Electric field due to semi-circular wire at a distance

Homework Statement A semi-circular wire containing a total charge Q which is uniformly distribute over the wire in the x-y plane. the semi-circle has a radius a and the origin is the center of the circle. Now I want to calculate the electric field at a point located on at distance h on the...
12. ### Angle between 2 charged spheres hanging from string

Homework Statement Two positively charged metal spheres are suspended from the same hook by light strings of equal length, making an angle of 10.0◦ with each other. The charges carried by the spheres are as shown in the diagram. After that, the spheres are brought in contact briefly, then...
13. ### Electric field created by point charges and conducting plane

I came upon this: http://physics.stackexchange.com/questions/174514/will-the-electrostatic-force-between-two-charges-change-if-we-place-a-metal-plat/323006#323006 question on Physics Stackexchange which I found very interesting. The configuration is basically two positive point charges q and...
14. ### I How to write the unit vector for the spherical coordinates

So I'm reading the Schaum's outlines while trying to prepare for a big test I have in September. And I'm trying to understand something here that maybe someone can offer some clarification and guidance. So, using Coulomb's Law, we can find the electric field as follows: dE...
15. ### Confused about coulomb law

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...
16. ### 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?
17. ### Coulomb law point charges

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...
18. ### Coulomb law - 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...
19. ### 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...
20. ### 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...
21. ### 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...
22. ### 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...
23. ### How to measure quantity of electricity without Coulomb law?

Or how did Coulomb measure quantity of electricity while doing his experiments that leads him to claim his famous Coulomb's law. F=k\frac{q_1 q_2}{r^2} You can measure F and r for sure. But how about q1 and q2 ?