What is Electric charges: Definition and 83 Discussions

Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. There are two types of electric charge: positive and negative (commonly carried by protons and electrons respectively). Like charges repel each other and unlike charges attract each other. An object with an absence of net charge is referred to as neutral. Early knowledge of how charged substances interact is now called classical electrodynamics, and is still accurate for problems that do not require consideration of quantum effects.
Electric charge is a conserved property; the net charge of an isolated system, the amount of positive charge minus the amount of negative charge, cannot change. Electric charge is carried by subatomic particles. In ordinary matter, negative charge is carried by electrons, and positive charge is carried by the protons in the nuclei of atoms. If there are more electrons than protons in a piece of matter, it will have a negative charge, if there are fewer it will have a positive charge, and if there are equal numbers it will be neutral. Charge is quantized; it comes in integer multiples of individual small units called the elementary charge, e, about 1.602×10−19 coulombs, which is the smallest charge which can exist freely (particles called quarks have smaller charges, multiples of 1/3e, but they are only found in combination, and always combine to form particles with integer charge). The proton has a charge of +e, and the electron has a charge of −e.
Electric charges produce electric fields. A moving charge also produces a magnetic field. The interaction of electric charges with an electromagnetic field (combination of electric and magnetic fields) is the source of the electromagnetic (or Lorentz) force, which is one of the four fundamental forces in physics. The study of photon-mediated interactions among charged particles is called quantum electrodynamics.The SI derived unit of electric charge is the coulomb (C) named after French physicist Charles-Augustin de Coulomb. In electrical engineering it is also common to use the ampere-hour (Ah). In physics and chemistry it is common to use the elementary charge (e as a unit). Chemistry also uses the Faraday constant as the charge on a mole of electrons. The lowercase symbol q often denotes charge.

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  1. C

    Electric field external to Conducting Hollow Sphere with charge inside

    I have read Griffiths' Chapter 2 sections on Conductors. According to it, (if I understood it correctly) if the charge is put inside the cavity of a conductor, then the equal and opposite total charge will be induced surrounding the cavity. This charge and the total charge induced surrounding...
  2. putongren

    No Electric Charges if No Electric Field in Region

    This is a conceptual question. I think we can conclude that electric charges cannot be present if there is no electric field in that region. Is this an application of Gauss' Law? A net electric flux thru a surface indicates that there is a charge within that region. An electric field must be...
  3. jackiepollock

    How to picture a radial field around a 3d object?

    Hello! First off, for a), I am not too sure how to picture a radial field around a 3d object. I know that this spherical metal dome is basically a enlarged version of an atom, but since with problems on radial field around an atom, I don't have to consider its diameter, I'm not sure how the...
  4. P

    I Moving charges in electrostatics

    According to a popular book on electrodynamics a special case of electrostatics is- ''source charges are stationary (though the test charge may be moving)''. My question is- now that the test charge is moving, how is it a special case of electrostatics anymore? Also many times we deal with...
  5. Tryhard314

    Salt water and potential difference

    Imagine a container of salt water at 0V (Relative to ground),Now you've put in it 2 electrodes,one at +500V (Electrode A), The other at +250V(Electrode b), Normally positive ions should go to the negative electrode , and Negative ions should go to the positive electrode , But in our example the...
  6. nashikin58

    How to avoid a clash of magnetic charge and electric charge

    Hi, now I'm working on a project which involves a dc motor and high voltage. I'm developing a machine consists of a motor to rotate a platform disc and high voltage will be applied during the rotation. The problem is when I supply a positive high voltage at motor shaft during rotation, the motor...
  7. C

    Work of external forces and electrostatic potential energy

    Homework Statement Two metal spheres of equal radius ##R## are placed at big distance one from the other. Sphere 1 has total charge ##q## and sphere 2 has no charge. The two speheres are moved one towards the other until they touch, then they are moved again far away one from the other. What is...
  8. mikemartinlfs

    Dual electron repulsion (momentum question)

    This is a multiple choice question that, after one incorrect attempt, I got correct; however, I want to actually understand what the explanation means. I'm hoping someone here can help. Homework Statement Two electrons, each with mass m and charge q, are released from positions very far from...
  9. U

    Electric charges and fields: Semicircular charge distributions

    Homework Statement If linear charge density is equal to 1micro coulomb per meter, then what is the electric field intensity at O? Homework EquationsThe Attempt at a Solution The electric fields due to the two straight lines should cancel out.. But how to progress further? Please let me know...
  10. U

    Electric charges and fields: Crossed dipoles

    Homework Statement Two short dipoles each of dipole moment p are placed art origin. The dipole moment of one dipole is along x-axis while that of other is along y axis. Then what will be the electric field at a point (a, 0)?Homework Equations The direction of electric field due to axial dipole...
  11. U

    Electric charges and fields: Charged conducting spheres touching then separated

    Homework Statement Two charged metallic spheres of same size repel each other by a force F. They are now touched with each other and are then separated to same initial distance. Now the force of repulsion is F'.Homework Equations On touching the spheres will reduce their charges... So the new...
  12. U

    Electric charges and fields

    Two identical small bodies each of mass m and charge q are suspended from two strings each of length l from a fixed point. This whole system is taken into an orbiting artificial then the tension in strings is... The answer has to be kq2/4l but how? Can someone please explain? Plus its not a...
  13. Dr. Who

    Finding number of charges using Coulomb's Law

    Homework Statement Please refer to the image; problem-1. My theory is that there are two spheres 'A' and 'B', where 'A' is (partially and primarily) positively charged, and 'B' is (partially and primarily) negatively charged. The magnitude of negative charge is greater than the positive charge...
  14. Phy_TR

    Help with Electric Forces Problem and Equilateral Triangles

    Homework Statement The point charges in the figure have the following values: q1=+2.1μC, q2=+6.3μC, q3=−0.89μC. Suppose that the magnitude of the net electrostatic force exerted on the point charge q2 in the figure is 0.57 N . Find the distance d and the direction (angle) of the net force...
  15. J

    Particles with electric charges visible to the human eye?

    Are there any particles known in the Physics world with an either positive or negative charge that can be viewed by the human eye under LED light illumination and have an attraction/repulsion to magnetism?
  16. S

    Electric Charges: Understand Electric Currents

    I am not able to understand electric currents. Can anyone explain?
  17. Robin04

    Electric Charge: Finding Q_1 Given Q_2 & r

    Homework Statement The distance between two small balls of the same radius and charge is r. If we release the balls they approach, touch and then repulse each other. When their distance is 4r the repulsive force is 1/20th of the initial force. What is the charge of the first ball if the...
  18. K

    Electric charges at the corners of a square

    Homework Statement 3 point charges, q1=+2E-9[Coulomb] are placed at the corners of a square of 0.2[m] edge. what is the potential at the center. Homework Equations The potential of a point charge at distance r: $$V[Volt]=K\frac{q}{r}$$ ##K=\frac{1}{4\pi\varepsilon_0}=9\times 10^9## The...
  19. J

    A question about moving electric charges and their force

    I want to find out whether I'm doing something wrong, and where to look for similar thinking. Imagine a thin wire that carries a constant electric current. Negative charges move to the right. Positive charges are stationary. The charges balance on average, or maybe there are a few more negative...
  20. A

    Where Do Electrons Move When Insulated Metal Spheres Are Brought Together?

    Suppose we have two insulated uncharged metal spheres,say X and Y, in contact with each other.A negatively charged object C is brought near X My first question is:Do all of the electrons move to the sphere Y since electrons are free to move? Then if X is touched momentarily with a finger,and...
  21. B

    Newton's 3rd Law and electric charges

    Hi, Is Newton's 3rd law applicable to electric charges? I have a problem with a situation where two identical positive charges moving perpendicular to each other. The magnetic forces exerted by each one on the other have same magnitude but their directions are not opposite.
  22. M

    Electric Charges Causing Centripetal Motion

    Homework Statement A particle of charge Q is fixed at the origin of an xy coordinate system. At t = 0 a particle (m = 0.671 g, q = 5.90 µC is located on the x-axis at x = 15.6 cm, moving with a speed of 54.4 m/s in the positive y direction. For what value of Q (in μC) will the moving particle...
  23. V

    Electric charges and conservation of energy

    Homework Statement Two charged particles connected by a string exert electric forces on one another. One has a mass of 3 grams and the other 6 grams. The string is .04m. The force is calculated to be 50.56N. What is the tension in the string? What is the total energy of the system...
  24. R

    Force on a point from electric charges

    Homework Statement What is the net force on the bottom charge? Please give the force in Fx and Fy Homework Equations F=qE E=kq/r^2 The Attempt at a Solution Fx=2.88x10^-9N Fy=-1.01x10^-4N These aren't correct. I used the equation above and used r=0.035m for both the side...
  25. S

    Metal Surface Repels Electric Charges - Applications?

    I came across this piece of news, about how researchers have found a way to repel electric charges away from a surface: http://phys.org/news/2013-01-metal-surface-repel-electric.html I was thinking that perhaps it could be useful for more than just particle accelerator experiments. Could...
  26. K

    Please help me with electric charges physics problem.

    Hello, please help me solve this so I can learn from it. Image: http://i48.tinypic.com/30k8y10.jpg Two charges with charge +Q are placed at A and C vertices of a rhombus with four even sides (α). A prticle with mass m and charge -Q is placed at vertex B. An unknown charge size of q is...
  27. R

    Help with Electric charges using coulomb's law

    Homework Statement Two point charges are located on the y-axis as follows: charge q1=-2.5nC at y=-0.6m, and charge q2=+3.5nC at the origin. What is the net force (x, y components) exerted by these two charges on a third charge q3=+5.0nC located at y=-0.4m? Homework Equations F=k...
  28. C

    Electric Charges Homework: Find q from Tmax & Fc2

    Homework Statement An electrically neutral model airplane is flying in a horizontal circle on a 2.5-m guideline, which is nearly parallel to the ground. The line breaks when the kinetic energy of the plane is 50 J. Reconsider the same situation, except that now there is a point charge of +q on...
  29. M

    What causes electric charges? Repulsion and attraction?

    Hi, I'm an undergraduate biologist student. I was studying chemical bond, but, while trying to understand it, I couldn't really get what causes the electric charges, what seems essential to me. So, someone can explains, in the simplest way as possible, what is electric charge? What causes it...
  30. A

    What causes electric charges to experience forces?

    What cause a particle with the property of electric charge to interact with other charges? My way of thinking is that due the natural isotropy of the electric field of the electric charges any other electric field near the charge would cause it to become anisotropic, thus causing acceleration in...
  31. T

    Change in potential energy/work formula for electric charges.

    I have the following formula on my formula sheet: ΔU = U_a - U_b = q(V_a - V_b) I was wondering if 'a' is final and 'b' is initial or is it the other way around? Also when I plug in my charge q into the formula, if it was a negative charge do I plug the negative sign into the formula? I...
  32. J

    Two Electric Charges- Electric Force-Ranking

    Homework Statement Below are seven arrangements of two electric charges. All of the charges are the same size, 20 C, but they are either positive or negative. Each figure also has a point labeled P that lies on a straight line with the two charges. The distance between any two items is all 5...
  33. N

    Would anything change electric charges could be complex numbers?

    Consider an Argand diagram that shows the number line (positive and negative) and the imaginary plane of other possibilities. As in, we have numbers that are positive and negative, and through complex numbers all of the polarities in between. I am using this as an analogy, because we have...
  34. P

    Electric Charges (max and min)

    A positive charge Q is on the y-axis at a distance a from the origin, and another positive charge q is on the x-axis at a distance b from the origin. A) For what values(s) of b is the x-component of the force on q a minimum? B) For what values(s) of b is the x-component of the force on q a...
  35. E

    Electric charges, wrong answer D: ?

    Homework Statement Find the net force at point A q1=-6x10^-5 C q2=-3x10^-5 C q1 is 3m north of A q2 is 3m east of A find the net force on a -1.2x10^-5 C charge The Attempt at a Solution first off I find how the electric field is with no charge at point A = 6.7 x 10^4...
  36. P

    Why field lines must begin or end on electric charges?

    Homework Statement Use Gauss' law to explain why field lines must begin or end on electric charges. Homework Equations Gauss' law: \epsilon_0 \phi_E=q The Attempt at a Solution I'm not sure whether this solution is incomplete or inconsistent. First, I take a gaussian surface...
  37. J

    Properties of electric charges - insulators and conductors

    Homework Statement I have some hypothetical questions. Question 1 There is a conductor with a single electron and proton inside of it. If we try to charge the conductor by induction, we might put a proton close to the conductor. The electron will go towards that proton while the proton in...
  38. F

    Physics Case: Electric Charges and Forces.

    Homework Statement Four punctual charges are located as shown in the figure below. A, B, and C are located at the vertices of an equilateral triangle. The values for these charges are A = +1.4microculombs, B = 4.5microculombs, C = -6.7microculombs and D = +7.1microculboms. THe length of the...
  39. E

    Velocity in relation to Electric charges.

    Homework Statement From a large distance away, a particle of mass m1 and positive charge q1 is fired at speed v in the positive x direction straight toward a second particle, originally stationary but free to move, with mass m2 and positive charge q2. Both particles are constrained to move...
  40. I

    Neutralizing Forces Between Electric Charges

    Homework Statement Consider a charge of +2.0 µC placed at the origin of an X-Y co-ordinate system and a charge of -4.0 µC placed 40.0 cm to the right. Where must a third charge be placed – between the charges, to the left of the origin, or beyond the second charge – to experience a net force of...
  41. A

    Coulombs Law & Electric Charges

    Homework Statement Two negative electric charges, (Charge A on the left, and Charge B on the right) each with a charge of 3.0 x 10-5 Coulombs are fixed at a distance of 2.9 meters from each other. Find the electric force of charge A on charge B. (Don't forget, if the force points to the left...
  42. H

    Electric Charges, Electric Forces and Electric Fields

    Homework Statement An object with a net charge of 24 x 10^-6 Coulombs is placed in a uniform electric field of 610 N/C, directed vertically. What is the mass of this object if it floats in this electric field? Homework Equations Felectric = kC (q*q/r^2) Electric Field= kC (q/r^2) E=...
  43. A

    Potential Energy of Electric Charges

    Hello all, my reason for posting is to clarify a topic of electrostatics that I recently covered in physics. I turned in an assignment and my teacher marked an answer wrong and gave a strange explanation of how to solve it. Here is my attempt at the solution. Homework Statement A charge of...
  44. G

    How to confine electric charges

    What sort of field do you need to confine electric charges? Is an electric field alone possible? Do the charges have to circle or can they be stationary? What parameters are important for this to work.
  45. P

    Resolving Vectors for Electric Charges

    Homework Statement Hi there, I am having a lot of trouble with this problem. Any help much appriciated. Thanks inadvance. Two point charges, each of 4x10-6C are placed 1m away at points A and B respectively. Calculate the electric field strength at a point P, which is a distance of 1m...
  46. L

    Electric Charges and Fields

    Homework Statement two charged spheres 4 cm apart attract each other with a force of 1.2x10^-9 . determin the magnitude of the charge on each if one has twice the charge (of the opposite sign) as the other.Homework Equations Fe = KQq/r^2 The Attempt at a Solution well you are only given Fe...
  47. C

    Why Does a Charged Ruler Attract a Current-Carrying Wire?

    I set up a simple experiment where a dc current carrying bare wire conductor runs parallel with a electrically charged plastic ruler. When no current flows in the wire and the ruler is charged with electrons (by rubbing it with a fur) the conductor will be attracted to the ruler. When dc current...
  48. D

    Electric Charges: Newton's Third Law & Tension

    Hi, I hve kind of a problem with this static electric question; There are two SIMILAR ping pong balls coated with aluminium paint and suspended using nylon string. Taking the imaginary line perpendicular to the wall, on which the balls are hanging from, to be the normal (although this is in...
  49. T

    Understanding the Components of Electric Charge Equation

    Homework Statement The question lies in the equation, I do not understand where the SQRT of 3Q or the 2L^2 is coming from? Can somebody help me with this? The professor kinda breezed by this but I cannot find a valid explanation anywhere! Thanks in advance!