What is Point charges: Definition and 359 Discussions

A point particle (ideal particle or point-like particle, often spelled pointlike particle) is an idealization of particles heavily used in physics. Its defining feature is that it lacks spatial extension; being dimensionless, it does not take up space. A point particle is an appropriate representation of any object whenever its size, shape, and structure are irrelevant in a given context. For example, from far enough away, any finite-size object will look and behave as a point-like object. A point particle can also be referred in the case of a moving body in terms of physics.
In the theory of gravity, physicists often discuss a point mass, meaning a point particle with a nonzero mass and no other properties or structure. Likewise, in electromagnetism, physicists discuss a point charge, a point particle with a nonzero charge.Sometimes, due to specific combinations of properties, extended objects behave as point-like even in their immediate vicinity. For example, spherical objects interacting in 3-dimensional space whose interactions are described by the inverse square law behave in such a way as if all their matter were concentrated in their centers of mass. In Newtonian gravitation and classical electromagnetism, for example, the respective fields outside a spherical object are identical to those of a point particle of equal charge/mass located at the center of the sphere.In quantum mechanics, the concept of a point particle is complicated by the Heisenberg uncertainty principle, because even an elementary particle, with no internal structure, occupies a nonzero volume. For example, the atomic orbit of an electron in the hydrogen atom occupies a volume of ~10−30 m3. There is nevertheless a distinction between elementary particles such as electrons or quarks, which have no known internal structure, versus composite particles such as protons, which do have internal structure: A proton is made of three quarks.
Elementary particles are sometimes called "point particles", but this is in a different sense than discussed above.

View More On Wikipedia.org
  1. U

    Electric potential at a point between 3 point charges

    Homework Statement Three pointcharges are located at the following points on an x-y coordinate system, Q1 = -3 uC at (0,0) q2 = 10.0 uc at (0,0.5m), and q3 = -3 uC at (x,0) . What is the total electric potential at the point (x/2,0) where x is in units of m. At what value does x have to be...
  2. S

    4 identical point charges on a rectangle's corners

    hi ,, I'm having this problem that i tried to solve but I couldn't so if anyone could help with EXPLANATION I would be greatful Homework Statement Four identical point charges (q = +10.0 µC) are located on the corners of a rectangle. The dimensions of the rectangle are L = 60.0 cm and W...
  3. S

    Electric field and electric potential for point charges problem

    Homework Statement Given two 1.80 µC charges at +/- 0.800 m from the origin and a positive test charge q = 1.30x10-18 C at the origin. What is the electric field at the origin due to the two 1.80 µC charges? What is the electrical potential at the origin due to the two 1.80 µC charges? related...
  4. Q

    Potential Due to a Group of Point Charges

    Homework Statement Homework Equations The Attempt at a Solution First time: I got -1.468e-19 which is wrong. Second time: I got -6.407e-19 which is wrong. q1 = 3.337e-19 ?
  5. M

    Ranking the force of point charges problem

    Homework Statement 5 point charges; q1; charge = +q distance = d q2; charge = +2q distance = 3d q3; charge = -3q distance = 2d q4; charge = -4q distance = 3d q5; charge = -5q distance = 2d are placed in the vicinity of an insulating spherical shell with a charge (+Q), distributed...
  6. M

    Ranking the force of point charges

    Homework Statement 5 point charges; q1; charge = +q distance = d q2; charge = +2q distance = 3d q3; charge = -3q distance = 2d q4; charge = -4q distance = 3d q5; charge = -5q distance = 2d are placed in the vicinity of an insulating spherical shell with a charge (+Q), distributed...
  7. C

    Electric potential energy and point charges

    Homework Statement Two point charges , Qz= +5.00 nanoC and Q2= -3.00 nanoC, are separated by 35.00 cm. a) What is the potential energy of the pair? What is the significance of the algebraic sign? b) what is electrical potential at a point midway between the charges? (here I'm supposing i'd...
  8. G

    Electric Field due to Multiple Point Charges

    Homework Statement Two point charges are placed on the x axis. The first charge, q1 = 8.00 nC, is placed a distance 16.0 m from the origin along the positive x axis; the second charge, q2 = 6.00 nC, is placed a distance 9.00 m from the origin along the negative x axis. Calculate the...
  9. M

    Coulomb's Law and Point Charges: Real World vs Theory

    1)What is the formal definition of a point charge? It is known, that coulomb's law , is valid for point charges? But the real world does not consist of point charges. And coulomb himself used two spheres in his experiments... 2)Another point, in many books I have found that they say, when...
  10. A

    Finding Tensions of Fixed Point Charges

    A fixed point charge of +2q is connected by strings to point charges of +q and +4q (see attached diagram), Find the tensions T_1 and T_2. For T_2, I start summing the forces on the +4q point charge. F_{net,4q}=F_{q}+F_{2q}+T_2 0=F_{q}+F_{2q}+T_{2} T_2=-(F_{q}+F_{2q}) Is this the...
  11. X

    The electric potential difference created by point charges.

    Homework Statement A charge of -3.00 C is fixed in place. From a horizontal distance of 0.0450 m, a particle of mass 7.20x10^-3 kg and charge -8.00 C is fired with an initial speed of 65.0 m/s directly toward the fixed charge. How far does the particle travel before its speed is zero...
  12. P

    Electric Fields and Point Charges

    Homework Statement Suppose you want to determine the electric field in a certain region of space. You have a small object of known charge, and in an instrument that measures magnitude and direction of the force exerted by object by the field. (a) The object has a charge of +20.0 C, and...
  13. A

    Coulombs Law - 3 point charges

    Homework Statement Three identical point charges A, B, and C are located in the shape of an equilateral triangle with sides of length 15 cm. What is the net force on B if each charge has a magnitude of -5.0 x 10-3 C? Homework Equations coulombs law equation The Attempt at a...
  14. J

    Point charges arranged as a trianngle

    Homework Statement Consider three charges at the vertices of an equilateral triangle of side a = 7 cm. qA = +2 µC, qB = +2 µC, and qC = -1 µC. (see attached picture) Find the x- and y- components of the electric force acting on qC Homework Equations i am doing everything right...
  15. B

    What Is the Charge of q2 When the Net Electric Field at Point P Is Zero?

    Homework Statement Two point charges, q1 and q2, are placed 0.30m apart on the x-axis, as shown in the figure(http://hiviz.org/apb89/ap/problems/2006-3.jpg" . Charge q1 has a value of -3.0x10^-9 C. The net electric field at point P is zero. A) What is charge of q2 (Positive/Negative) B)...
  16. S

    Solving Two Point Charges: Calculating Electric Field

    Homework Statement Two point charges are 10.0 cm apart and have charges of 2.0 uC ( the u is supposed to be a greek symbol where the left side of the u is extended down) and -2.0 uC, respectively. What is the magnitude of the electric field at the midpoint between the two charges...
  17. R

    Electric field from two point charges and then some

    Homework Statement A point charge, q1, has a charge of 3.4x10^-9 C. A second point charge, q2, is place 2.1x10^-6 m to the right of q1; it has a charge of -10.2x10^-9C. A) What is the magnitude of the field 8 mm to the left of the centre of the two charges? B) You could also treat...
  18. K

    Net Force of Point Charges, Coulomb's law

    Homework Statement The drawing shows three point charges fixed in place. The charge at the coordinate origin has a value of q1 = +8.02 C; the other two have identical magnitudes, but opposite signs: q2 = -4.73 C and q3 = +4.73 C. (a) Determine the net force exerted on q1 by the other two...
  19. B

    Potential energy of point charges

    I am puzzled by the solution to a problem in electrical potential. The situation involves three identical point charges (same charge, same mass) each one placed at a corner of a square. The charges are released simultaneously and the problem is to find the maximum speed attained by each of them...
  20. R

    Electric field produced by 2 point charges

    Homework Statement A small object A, with a charge of -2.78x10^-10 C, creates an electric field. At a point P located 0.250 m directly north of A, the field has a value of 40.0 N/C directed to the south. If a second object B with the same charge as A is placed at 0.250 m south of A (so that...
  21. T

    Point charges hanging on a string

    Homework Statement What would be the angle theta as shown in the picture, if the 5 gram balls hangin off 1m strings have been charges to 100nC each http://img178.imageshack.us/img178/5103/mooche.th.jpg The Attempt at a Solution I'm not really sure how to solve such a question...
  22. E

    Calculating voltage from multiple point charges

    Homework Statement A point charge 10 km in the air with a charge of 40 coulombs A point charge 5 km in the air with a charge of -40 coulombs A point chare 2 km in the air with a charge of 10 coulombs -Find the electric potential due to these charges at a point which at a height of 8 km and...
  23. A

    Electric Potential/Work - POint Charges on a Square

    Homework Statement two identical point charges are on diagonally opposite corners of a square that is 0.5m on a side. Each charge is +3 x 10^ -6 C. How much work is done by the electric force when 1 charge moves to an empty corner? Homework Equations W= u= qV = q(kq/r) = kq^2/ r (is this...
  24. T

    Coulomb's law, balancing a ball with point charges

    3 equal charges q are at the vertices of an equilateral triangle as shown, with the z-axis running through the midpoint of the triangle (such that the distance from each charge to the midpoint is d) http://img111.imageshack.us/img111/7159/graphieew7.th.jpg a bead of charge Qb (of equal...
  25. Z

    Calculating point charges and ratio of electrostatic force to weight

    Homework Statement Measurements show that a honeybee in active flight can acquire an electrostatic charge on the order of 93 pC. a)How many electrons much be transferred to produce this charge? Ne = * b) Supposing two bees, both with this charge, are separated by a distance of 12 cm...
  26. M

    Epotential of Point Charges - Really Hard Conceptual Problem

    A thick spherical shell of charge Q and uniform volume charge density p is bounded by radii r1 and r2, where r2 > r1. With V = 0 at infinity, find the electric potential V as a function of the distance r from the center of the distribution, considering the regions (a) r > r2, (b) r2 > r > r1...
  27. I

    Electric field and point charges

    Homework Statement The question is as seen on the attachment. Homework Equations E = (k)(q)/r^2 The Attempt at a Solution I know that for this question I am supposed to use the equation "E = (k)(q)/r^2" but the question has me kinda confused. Could someone please tell me what my...
  28. E

    Point charges in a line; electric field

    Homework Statement Three point charges are on the x-axis at 0m, 0.2m, and 0.4m, with charges -19microC, +19microC, and +19microC respectively. There are two places where the electric field is zero. One is between 0.2 and 0.4m. Where is the other place? Homework Equations i used the...
  29. S

    Calculating Electric Forces and Fields for Multiple Point Charges

    A charge of 1.2x10^-3C is fixed at each corner of a rectangle that is 30cm wide and 40cm long. What is the magnitude and direction of the electric force on each charge? What is the electric field and the electric potential at the centre? This is the question i am currently trying to solve...
  30. R

    Electrostatics - force on point charges by electric field

    Homework Statement A square, with each corner as a point charge, A, B, C, and D. They all have the same charge of 5.0 x 10 ^(-6) C. Length of each side of the square is 0.1 m. 2 negative charges diagonal from each other, and the other two are positive, diagonal from each other. Question asks...
  31. L

    Help with point charges and electric fields

    Homework Statement So the question states: Four point charges, each of magnitude q, are located at the corners of a square with sides of length a. Two of the charges are +q and two are -q. The charges are arranged in one of the following two ways: (1) The charges alternate in sign...
  32. J

    Position three point charges so net force is zero

    Homework Statement li have three charges, 2 with same charge (magnitude and sign) and 1 with a smaller charge(smaller magnitude and opposite sign to the other two). how would i position them on a line so that the net force on any of them is zero Homework Equations electric force, F =...
  33. T

    Electric field of point charges

    hey guys i can't figure out this problem to save my life i thought i was doing it right using the K=q/r^2 formula but its not coming out right. so if anyone can help me with this problem i would very much appreciate it. In a rectangular coordinate system, a positive point charge = 3.50 is...
  34. B

    Point Charges and Force vector addition

    Hi. I would appreciate some help with this point charge problem. I think I understand the general set up, but don't know where to go from there. Homework Statement Two point charges are placed on the x-axis as follows: Charge q1 = +4.00nC is at x=0.400m, and charge q2 = +2.00nC is at...
  35. G

    Electric field from two point charges

    Homework Statement Three point charges are located at the corners of an equilateral triangle as in the figure below. Find the magnitude and direction of the net electric force on the 1.00 µC charge. (A = 1.00 µC, B = 6.50 µC, and C = -4.20 µC.) magnitude N direction °...
  36. D

    Point Charges in a Square: Could the Force on Each Be Zero?

    Homework Statement A charge Q is fixed at each of two opposite corners of a square, while a charge q is fixed at the other two corners. (a) if the resultant electrical force on Q is zero, how are Q and q related? (b) could q be choosen to make the resultant electrical force on every charge...
  37. C

    Solving for Electric Potential Energy , given 4 point charges of equal value

    Homework Statement Four point charges are individually brought from infinity and placed at the corners of a square whose sides are 0.30 m each. Each charge has the identical value + 4.0 mC. What is the electric potential energy of these four charges? Homework Equations V=kq/r (or...
  38. A

    Electric Flux due to Two Point Charges: Analysis and Calculations

    A point charge q_1 = 3.40 {\rm nC} is located on the x-axis at x = 1.80 {\rm m}, and a second point charge q_2 = -5.80 {\rm nC} is on the y-axis at y = 1.10 {\rm m} What is the total electric flux due to these two point charges through a spherical surface centered at the origin and with...
  39. S

    Exploring the Magnetic Moment of Point Charges

    why we take electrons as point particles? just because of its magnetic moment? maybe there is something wrong with the idea of the magnetic moment of a point charge. i appreciate if you help.
  40. K

    Two point charges, Zero Net Force

    [SOLVED] Two point charges, Zero Net Force Homework Statement Two point charges of charge 7.40 μC and -1.80 μC are placed along the x-axis at x = 0.000 m and x = 0.300 m respectively. Where must a third charge, q, be placed along the x-axis so that it does not experience any net force because...
  41. R

    Electric Potential between two point charges

    Homework Statement Two point charges Q1 = +5.00 nC and Q2 = −3.00 nC, are separated by 35.0 cm. (a) What is the electric potential at a point midway between the charges? (b) How much energy is required to bring an electron, located at infinity, to this midway point? Homework Equations...
  42. S

    Potential due to a the sum of point charges?

    Homework Statement Q15. Eight identical spherical raindrops are each at a potential V, relative to the potential far away. They coalesce to make one spherical raindrop whose potential is: A. V/8 B. V/2 C. 2V D. 4V E. 8V Homework Equations V = sum( Vi ) The Attempt at a...
  43. A

    Involves magnetic force and point charges with constant velocity.

    A point charge is moving at 1 x 10^6 meters per second. At the origin (0,0), a magnetic field of 1 T is applied into the page. The charge = 1.6 x 10^/10 C. 1) Calculate the force. 2) Calculate the exact location it hits the X intercept. 3) Calculate the time is takes to hit the X intercept...
  44. B

    How Far is Charge C from Charge A When the Force on It Is Zero?

    Homework Statement Charge A and charge B are 3.00 m apart, and charge A is +2.00 C and charge B is +3.00 C. Charge C is located between them at a certain point and the force on charge C is zero. How far from charge A is charge C? Homework Equations The Attempt at a Solution I am...
  45. N

    Magnitude of electric field using point charges

    [SOLVED] Magnitude of electric field using point charges Homework Statement Two charges, Q1 = 3.15 μC and Q2 = 5.40 μC, are located at points (0, -2.80 cm) and (0, +2.80 cm), What is the magnitude of the electric field at point P, located at (5.45 cm, 0), due to Q1 alone? lQ2 l l l...
  46. N

    Electric Fields- point charges

    [SOLVED] Electric Fields- point charges Homework Statement Two point charges of charge 7.40 μC and -1.60 μC are placed along the x-axis at x = 0.000 m and x = 0.360 m respectively. Where must a third charge, q, be placed along the x-axis so that it does not experience any net force because...
  47. M

    Calculate Electric field from two point charges

    [SOLVED] Calculate Electric field from two point charges Homework Statement Two point charges with q1=2x10^-5 and q2=-4x1-^-3 are located in free space at (1,3,-1) and (-3,1,-2), respectively, in a cartesian coordinate system. Calculate the electric field E at (3,1,-2) Homework Equations...
  48. M

    Electric fields two point charges

    i just need to get this question over with i tried and tried but i couldn't get the right answer plss anyone u.u 1. Homework Statement point charges q1 = -6q and q2 = +3q are separated by distance d. Locate the point (measured from the origin at q1) at which the electric field due to...
  49. G

    Electric Field between 2 Point Charges

    [SOLVED] Electric Field between 2 Point Charges Homework Statement http://session.masteringphysics.com/problemAsset/1011305/15/1011305A.jpg Two point charges are placed on the x axis. The first charge, q1 = 8.00 nC, is placed a distance 16.0 m from the origin along the positive x axis...
  50. M

    Point Charges and electric field

    Homework Statement A positive point charge Q1 = 1.9 x 10^-5C is fixed at the origin of coordinates, and aa negative charge Q2 = -6.5 x 10^-6C is fixed to the axis at x = +2.0m. Find the location of the place(s) along the x-axis where the electric field due to these two charges is zero. IF...
Back
Top