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.

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    Question about this situation with two point charges +Q and -Q

    Would the magnitude of the net electric force on a charge +Q in a case where there is another charge -Q a distance x away from +Q be equal to the force on +Q by -Q in a case where there is a neutral metal rod between them? (and same distance x away from each other) I would be inclined to say...
  2. M

    Electric field of discrete point charges

    Five equal negative point charges (-q) are placed symmetrically around a circle of radius R. Calculate the electric field at the center of the circle. My Answer: Each one will be place 72 degrees from the other one (360/5), Each field line is directed toward the center (charges are...
  3. P

    Calculating Potential at Point C with Equal Charges on an Equilateral Triangle

    Points A,B and C are at the corners of an equilateral triangle of side 3 metres. equal positive charges of 2 micro-Coulombs are at A and B respectively. What is the potential at C??
  4. P

    Calculating Charge of 3 Identical Point Charges

    Three identical point charges, each of mass 140g and charge +q, hang from three strings. If the lengths of the left and right strings are each 10 cm, and each forms an angle of 48 degree with the vertical, determine the value of q.
  5. P

    Point charges on square - find magnitude of force

    Four point charges, each of magnitude 12.92 x 10^-6 C, are placed at the corners of a square 65.5 cm on a side. Given K_e = 8.98755 x 10^9 Nm^2/C^2. If three of the charges are positive and one is negative, find the magnitude of the force experienced by the negative charge. Answer in units of N...
  6. M

    Electric Field at the Center of a Square of Point Charges

    *sigh*, Another long semester of physics... Anyways, here we go ! Here's the problem: Calculate the magnitude of the electric field at the center of a square with sides 27.3 cm long if the corners, taken in rotation, have charges of 1.10 microC, 2.20 microC, 3.30 microC, and 4.40 microC...
  7. M

    How to Calculate and Measure Electrical Forces: Point Charges Problem 22

    Problem 22. Two positive point charges, each of which has a charge of 1.9*10^-9C, are located at y=0.38m and y=-0.38m. a. Find the magnitude of the resultant electrial force on a charge of 1.8*10^-9 C located at x=0.28m. Answer in N. Note: I used a^2+b^2=c^2 to find r in Coluomb's law...
  8. M

    What is the force between the two point charges?

    The electrostatic force between two point charges is 5.7*10^-4N. The charge on one of the point charges triples and the distant between the points doubles. What is the force between the two point charges?
  9. S

    Two positive point charges Q are held on the x-axis at x = a and at x = -a

    I've been doing this question, but can't seem to get past a particular bit. here's the question: 'Two positive point charges Q are held on the x-axis at x = a and at x = -a. A third positive point charge q, of mass m, is placed on the x-axis away from the origin at coordinate x such that |x|...
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