What is Coulomb's law: Definition and 403 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,





|

F

|

=

k

e






|


q

1



q

2



|



r

2






{\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.

View More On Wikipedia.org
  1. D

    How Does Changing Distance Affect Force Between Charges?

    Homework Statement By what factor must you change the distance between two point charges to change the force between them by a factor of ten? Homework Equations F1=kq1/r^2 F2=kq2/r^2 The Attempt at a Solution F1:F2= 10 r1/r2=sq.root(F2/F1)= 1/sqroot10 I do not understand...
  2. C

    Calculating Net Force on a Point Charge in a 2D Coulomb's Law System

    Homework Statement Consider the arrangement of point charges shown below. Calculate the net force on point charge 1 given the arrangement of the point charges and the separation of the charges. 1=2=3=e- 2=e+ r=0.4cm =0.0004m K=9x10^9 Fnet=? Please use this link for an image of...
  3. R

    Coulomb's Law and microcoulombs

    There are four charges, each with a magnitude of 2.5 microcoulombs. Two are positive and two are negative. The charges are fixed to the corners of a 0.29-m square, one to a corner, in such a way that the net force on any charge is directed toward the center of the square. Find the magnitude of...
  4. B

    Coulomb's law particles that form a square problem

    Homework Statement In the figure, four particles form a square. The charges are q1 = q4 = Q and q2 = q3 = q. (a) What is Q/q if the net electrostatic force on particles 1 and 4 is zero? Homework Equations F=8.99E9 Nm^2/c^2 [abs(q1)abs(q2)]/r^2 The Attempt at a Solution I made up...
  5. Saladsamurai

    Coulomb's Law (should be easy)

    Homework Statement Two equally charged particles are held 3.2*10^(-3)m apart and released from rest. The initial acceleration of the first is 7 m/s^2 and that of the second is 9 m/s^2. If the mass of the first is m1= 6.3*10^(-7) kg, what are a) the mass of the second particle and b) the...
  6. B

    Coulomb's Law - Could a mass term be missing?

    The near identity of Coulomb's law and Newton's law of gravitation is interesting to consider in light of the recent unexpected greater velocity (or acceleration) of deep space probes. If we add a mass term to Coulomb's law and a charge term to Newtons' law, then they are nearly the same...
  7. M

    Coulomb's Law dealing with electrons & protons?

    Styrofoam is a polymer containing carbon and hydrogen. Assume the formula is C8H8. How many molecules are in a 0.2 g styrofoam peanut? How many protons and electrons are in this peanut if it carries no excess charges? How many coulombs of positive and negative charge does this represent? If the...
  8. T

    Quick vector question (involving coulomb's law)

    Homework Statement Homework Equations It's given in the answer box. The Attempt at a Solution Basically, I found that equation for the magnitude of the force experienced from particle 0 by particle 3. I know it to be correct. However, vectors have always confused me, could...
  9. manjuvenamma

    Coulomb's law universal or not?

    What exactly is meant by universal law? I have read in a book a that Ohm's law is not a univeral law. I somewhat understood that as Ohm's law is not obeyed by all materials and not always. But I read now in another book that Coulomb's law is also not a universal law. Now I am beginning to...
  10. S

    Coulomb's Law and electron placement

    Homework Statement A point charge of -0.35nC is fixed at the origin. Where must an electron be placed in order for the electric force acting on it to be exactly at it's weight. Homework Equations Fe=Kqq/d^2 The Attempt at a Solution All I know is that n is an exponential value of...
  11. Saladsamurai

    Help with Coulomb's Law: Solving for Charges on Identical Spheres

    !Coulomb's Law! So I have already solved this one before, but I was redoing it fir practice when I encountered something that is troubling me. Depending on how I choose to solve my two equations, I get different results. Surely I am doing something wrong, but I cannot see it. Problem Two...
  12. K

    Coulomb's Law question - find initial charge

    [SOLVED] Coulomb's Law question - find initial charge Homework Statement Two identical small metal spheres with q1>0 and |q1| > |q2| attract each other with a force of magnitude 55.4 mN. They are separated by a distance of 3.94 m. The radius of each sphere is 40 micro-Newtons. The...
  13. Saladsamurai

    Why is one of the solutions obtained using Coulomb's Law not valid?

    [SOLVED] Question about Coulomb's Law I just solved this a problem in my text: Particle 1 of charge +1.0 uC and particle 2 of charge -3.0 uC are held at a separation L=10.0 cm on an x-axis. If particle 3 of unknown charge q3 is to be placed such that the net electrostatic force on it from 1...
  14. Saladsamurai

    Solving Charges: Coulomb's Law Puzzle

    Stupid Charges! Two identical conducting spheres, fixed in place, attract each other with an electrostatic force of .108 N when their center-to-center separation is 50 cm. The spheres are then connected by a thin conducting wire. When the wire is disconnected, the spheres repel each other with...
  15. Saladsamurai

    Net Force of a charged particle (Coulomb's Law)

    Homework Statement I really can't see where I am going wrong here. I would latex out my work, but it would take way too long, so I have scanned it in. It should be easy enough to read though. Its NUMBER 7, fig 21-22 Also the blurr says '100 nC' The Attempt at a Solution
  16. D

    Coulomb's Law: Does Charge Depend on Size?

    Homework Statement Suppose you let identical pith balls come in contact to make q1=q2 would the charges be equal if the pith balls were of different size? Homework Equations F=k(q1)(q2)/r^2 The Attempt at a Solution I would think they wouldn't be, because doesn't the charge...
  17. J

    Rotating Electric Forces: How to Find X Values to Change Net Force Direction?

    Homework Statement Particles 2 and 4, of charge -e, are fixed in place on the y-axis at y2=-10.00 cm and y4=5.00cm. Particles 1 and 3, of charge -e, can be moved along the x axis. Particle 5 of charge +e is fixed at the origin. Initially particle 1 is at x1= -10.0cm and particle 3 is at x3=...
  18. M

    Estimating charges coulomb's law

    this is my first time posting here in the forums right now I am really stuck with this problem i already tried solving it on my own but i can't i will really apreciate any feedback or hint i could use to solve it U_U Estimating Charge Two hard rubber spheres of mass ~20 g are rubbed...
  19. M

    Estimating charges coulomb's law

    this is my first time posting here in the forums right now I am really stuck with this problem i already tried solving it on my own but i can't i will really apreciate any feedback or hint i could use to solve it U_U Estimating Charge Two hard rubber spheres of mass ~20 g are rubbed...
  20. N

    Where Should the Third Charge Be Placed for Equilibrium on the X-axis?

    Homework Statement Two point charges lie on the x-axis. A charge of +7.7 uC is at the origin, and a charge of -4.4 uC is at x = 10.0 cm. At what position x would a third charge q3 be in equilibrium? Homework Equations F = k(q1)(q2)/r^2 The Attempt at a Solution This was how I...
  21. A

    Coulomb's law and String Tension

    Homework Statement Two small pith balls, each of mass m = 12 g, are suspended by 1.2 m fine (so that we can neglect their mass in this problem) strings and are not moving. If the angle that each string makes with the vertical is q = 42.6, and the charges on the two balls are equal, what is...
  22. J

    Finding Equilibrium Position for Three Charged Particles

    [SOLVED] Coulomb's Law The charges and coordinates of two charged particles held fixed in an xy plane are q1 = +3.5 µC, x1 = 3.0 cm, y1 = 0.50 cm, and q2 = -4.0 µC, x2 = -2.0 cm, y2 = 1.5 cm. At what coordinates should a third charge q3 = +5.5 µC be placed such that the net electrostatic force...
  23. B

    Coulomb's Law vs. Gauss's Law Paradox

    From Coulomb's law, as the distance between a charged particle and another charged particle approaches zero, the electrostatic force between the two particles approaches infinite. However, according to Gauss's Law, we know that for a uniformly charged sphere or spherical shell, the charge...
  24. U

    Gauss's and Coulomb's law forms and gravitational field

    Consider int(E.dA)=q/e, guass law relating the electric field to the charge enclosed. One can also derive (using the more mathematical version of guass' law - involving the double integral) this same formuala for a graviational field. Here the permitivitty constant would be replaced by...
  25. F

    Electric Charge and Coulomb's Law

    Coulomb's Law Problem - Please Help Homework Statement Two positive charges +Q are held fixed a distance d apart. A particle of negative charge -q and mass m is placed midway between them, then is given a small displacement perpendicular to the line joining them and released. Show that the...
  26. R

    Deriving Gauss's Law Without Coulomb's Law

    Hi, can you derive Gauss's Law without using Coulomb's Law? If so, how? Thanks
  27. S

    Coulomb's Law Question with Charges on x-axis

    Homework Statement Three point charges are placed at the following points on the x-axis: +2.0 micro Coulombs at x=0; -3.0 micro Coulombs at x=40 cm; and -5.0 micro Coulombs at 120 cm. Find the force on the -3.0 micro Coulomb charge. Homework Equations Coulomb's Law: Fe= k * qq' /...
  28. E

    Are Gauss's Law and Coulomb's Law Equivalent?

    Gauss's law may be used to derive Coulomb's law. I've never seen it done the other way around. Is this possible? Because I have not seen it, I infer that these forms are not logically equivalent.
  29. P

    Who Discovered Coulomb's Law and the Concept of Electric Field Lines?

    Does anyone know when Coulomb discovered his law? And does anyone know when the concept of electric field lines was invented? I know that Faraday created the idea for the magnetic field and I was wondering if it was he who applied it to the electric field or was it someone else? Sources of...
  30. U

    Coulomb's Law and charged particles

    1. Homework Statement Hi, I would appreciate it if someone could help me with this question, I am a n00b here Please and thank you Okay here's the question. The particles have charges Q1 = -Q2 = 100nC and Q3 = -Q4 =200nC and distance a = 5.0cm. What are the x and y components of the...
  31. P

    Scalar's form of Coulomb's Law

    Title: Scalar form of Coulomb's Law? Homework Statement Homework Equations Coulomb's Law Vector Form: \vec{F}_{12} = {\frac{{{k}_{e}}{{q}_{1}}{{q}_{2}}}{{r}^{2}}{\hat{r}_{21}}} Magnitude Form: |\vec{F}_{12}| =...
  32. I

    Solve Coulomb's Law Problems with Square of Charges | Helpful Tips

    Hi guys, these are the final 2 problems that I've been struggling with for the past day. Please help 1. Four point charges are situated at the corners of a square with sides of length a, as in Figure P15.4. Figure P15.4 Find the expression for the resultant force on the positive...
  33. I

    How Much Charge Would the Moon and Earth Need to Replace Gravity?

    1. The Moon and Earth are bound together by gravity. If, instead, the force of attraction were the result of each having a charge of the same magnitude but opposite in sign, find the quantity of charge that would have to be placed on each to produce the required force. 2. Fe = ke...
  34. K

    Coulomb's Law to find the net force

    Homework Statement Charge 8e-18 C is on the y-axis a distance 2 m from the origin and charge 9e-18 C is on the x-axis a distance d from the origin. The Coulomb constant is 8.98755e9 Nm^2/C^2. What is the value of d for which the x component of the force on 9e-18 C is the greatest...
  35. S

    Coulomb's law and drawing vectors

    Homework Statement Three charges are on the x~axis about five cm apart. Charge A is three micro C, charge B is negative four micro C, and charge C is five micro C. What is the effect on B? Homework Equations I have no idea how to solve this or the formula involved. The Attempt at a...
  36. F

    Coulomb's Law and spheres Problem

    Homework Statement Of the charge Q initially on a tiny sphere, a portion q is to be transferred to a second, nearby sphere. Both spheres can be treated as particles. For what value of q/Q will the electrostatic force between the two spheres be maximized? Homework Equations...
  37. P

    Understanding Coulomb's Law: Force of Repulsion Between Charged Objects

    Actually, this is not a homework question, but more of a concept problem (Sorry I can;t follow the format). We are given that the force of repulsion or attraction between 2 charged objects can be represented by : Fe = (Kq1q2)/d^2. Does this mean that the sum of the force between both objects...
  38. F

    Help with Coulomb's Law problem needed.

    Homework Statement In Fig. 21-26, particle 1 of charge +1.0 microCoulombs and particle 2 of charge -3.0 microCoulombs are held at separation L = 10.0cm on an x axis. If particle 3 of unknown charge q3 is to be located such that the net electrostatic force on it from particles 1 and 2 is zero...
  39. K

    Question Concerning Coulomb's Law

    One of Newton's laws(1 or 2) states that every force has an equal and opposite force. Coulomb's law describes subatomic particles interacting with one another. Electrons repel each-other relative to their distance while attracting protons relative to each-other. My question is, will the...
  40. S

    Problem from Electric Forces: Coulomb's Law section

    Hello, I'm having problems with the following question: Neutral metal sphere A, of mass 0.10 kg, hangs from an insulating wire 2.0 m long. An identical metal sphere B, with charge -q, is brought into contact with sphere A. The spheres repel and settle as shown. Calculate the initial Charge on...
  41. N

    Coulomb's Law (positive & negative charges)

    I need to draw a single point charge with a magnitude of +4.3 C (coulomb's) I want to make sure that I am doing this right so: If one electron equals 1.602*10^-19 C than +4.3 C is actually a negative charge and therefore -4.3 C would be a positive charge. Is this right or do i have it...
  42. N

    How Does Charge Distribution Affect Electric Field at the Center of a Bent Rod?

    Homework Statement A rod is bent into a semi circle of 180 degrees. The bottom half has a charge of -q and the top half a charge of q. Find the electric field at the center of the circle, point P. Homework Equations E = kq/r^2 The Attempt at a Solution I tried to set up an...
  43. A

    Electric Field & Coulomb's Law Problem

    Homework Statement A small 2g plastic ball is suspended by a 20 cm long string in a uniform electric field. If the ball is in equilibrium when the string makes a 15 degree angle with the vertical as indicated, what is the net charge on the ball? Here's the diagram...
  44. A

    What is the magnitude of charge on each sphere?

    Homework Statement Two small metallic spheres, each of mass 0.2g are suspendedas pednulums by light strings from a common point. The spheres are given the same eletric charge, and it is found that they come to equilibrim when each stringis at an angle of 5degrees with the vertical. If each...
  45. M

    How Far Must a Proton Be from a Charge to Balance Its Weight?

    Homework Statement A point charge q = -0.80 nC is fixed at the origin. Where must a proton be placed in order for the electric force acting on the proton to be exactly opposite to its weight? (Let the y-axis be vertical and the x-axis be horizontal.) Homework Equations F=(kq1 q2)/r^2...
  46. T

    Coulomb's Law (Electricity and Magnetism) Question

    Homework Statement Five point charges on a straight line are separated by a distance of 0.01 m. For what values of q2 and q4 would the net force on each of the other three charges be zero? q1-----q2-----q3-----q4-----q5 Where: q1= 2x10^-6 C q3= 1x10^-6 C q5= 2x10^-6 C Homework...
  47. S

    Coulomb's Law and repulsive force

    Homework Statement Charges q1 and q2 exert repulsive forces of 15 N on each other. What is the repulsive force when their separation is increased so that their final separation is 160% of their initial separation? a.1.3 N b.9.8 N c.8.7 N d.5.9 N Homework...
  48. C

    Finding Charge Using Coulomb's Law

    Ahhh, just typed out a big long post and I did something wrong and now it's gone. Oh well. This problem was given on a practice problem sheet in my first year university physics class. Homework Statement You have a lightweight spring whose unstretched length is 4.0 cm. You're curious to...
  49. B

    The Development of Coulomb's Law

    Hello, I am new here. I have a question that I cannot seem to find an answer to and is beginning to bother me in the worst way. I was researching to find out how Coulomb developed the formula that is used today (since I do not have the programme, I shall not even attempt to write it) and found...
  50. M

    Electrostatics coulomb's law problem

    Homework Statement how to use coulomb's law to find the r value of the three points when the total distance is 50 cm Homework Equations f=Kqq/r^2 The Attempt at a Solution i assumed that is it was uniform and sais r1+r2=r3 but now i think that is wrong
Back
Top