Electric charge Definition and 274 Threads

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

    Determining Electric Charge of a Bullet in Earth's Magnetic Field

    1. Homework Statement In a certain region, the Earth's magnetic field has a magnitude of 5.30e-5 T and is directed north at an angle of 57° below the horizontal. An electrically charged bullet is fired north and 11° above the horizontal, with a speed of 681 m/s. The magnetic force on the...
  2. X

    Electric field - find earths electric charge

    Homework Statement Measurments indicate that there is a weak electric field of 150 N/C surrounding the Earth that points towards the center of the earth. Determine the absolute value of the electric charge of earth. Homework Equations F|e| = ma |E| = |Fe| / |qt| |E| = k|qs| / r^2...
  3. D

    Single positive electric charge in a closed universe

    Say, all objects in a closed Universe are neutral, and there is only 1 (unbalanced) positive charge. Lines of an electric field started on a positive charge can end only on the negative charge or they go into infinity. But in a closed universe there are no negative charges nor they can go...
  4. N

    Electric charge and spontaneous symmetry breaking

    Hi, If I have a Lagrangian of complex scalar field (just U(1) local invariance). And I know that phi^star describes field with -e electric charge and phi describes field with e electric charge. How do I apply "charge issue" when I write Lagrnangian after spontaneous symmetry breaking in...
  5. R

    How Does the Electric Potential Vary with Distance from a Uniformly Charged Rod?

    Electric charge is distributed uniformly along a thin rod of length a, with total charge Q. Take the potential to be zero at infinity. Find the potential at the following points: P is distance x from (0,0) which is the right side of the rod. Find the potential at the point P, a distance to...
  6. B

    Electric Potential: Electric charge surrounded by two spherical shells

    Homework Statement A point charge q = -8 μC is surrounded by two thick, conducting spherical shells of inner and outer radii a1 = 0.3 m, a2 = 0.4 m, a3 = 0.7 m, and a4 = 0.8 m respectively. The inner shell is uncharged; the outer shell has a net charge Q = -10 μC. At this point in the...
  7. I

    Generating electricity from electric charge?

    If I have a really big charged object, is it possible to direct the charges to an object/the same place and generate current/electricity from it? It was just something I thought of, totally random, but I'd like to know the reasoning behind it C:
  8. 1

    How Does Electron Transfer Affect Human Net Charge?

    Homework Statement Human tissue contains about 3·10^27 electrons per kg of material. Suppose two humans each have a mass of 50 kg. We now transfer 0.0005 % of the electrons from the male human to the female. What are the net charges of the two humans afterwards? Homework Equations 1...
  9. P

    How to Determine Charge Density on a Plane from a Point Charge?

    Homework Statement hello, the problem is that i have charge q which lies in d distance from a plane and I need to find function \sigma which describes density of this charge The Attempt at a Solution I wrote this situation in cylindrical coordinate system where q lies in point A=(0,0,h) and...
  10. G

    Electric charge and electric feild prblem

    Homework Statement A charge of 6.00 mC is placed at each corner of a square 0.100 m on a side. Determine the magnitude abd direction of the force on each charge. Homework Equations The Attempt at a Solution
  11. C

    Law of conservation - electric charge, brain death

    Hey there, So I'm a bit of a newbie on this, and I'm just kind of wondering on this subject... But could someone give a brief description of how conservation laws apply to electric charge? And more specifically, I'm thinking in terms of how it applies to synapses and such in the brain...
  12. W

    Some questions about ELECTRIC CHARGE ADN ELECTRIC FIELD

    1.If you charge a pocket comb by rubbing it with a silk scarf, how can you determine if the comb is positively or negatively charged? 6.Contrast the net charge on a conductor to the "free charges" in the conductor. 7.A charged rod placed near an unchanged metal object can attract(or repel)...
  13. V

    Total electric charge on the earth,

    Homework Statement The Earth can be regarded as a sphere of radius R, the volume density of charge distributed as \rho = \frac{\rho_s r}{R} where the density is 0 at thcce centre and rises linearly with radius until it reaches ps at the Earth's surface i) prove that the total charge on...
  14. J

    Earth as a giant sphere of electric charge

    I'm not a science student. So, I humbly request you to limit yourself to the basics, please do not indulge in infighting. If you ignore the request, you would be investing your efforts at the wrong place and perhaps it would be considered a pretentious show of knowledge. If a gold leaf...
  15. PrincePhoenix

    What Does Fractional Electric Charge Mean in Quarks?

    According to the third paragraph over here, http://www.particleadventure.org/quarks.html "Quarks have the unusual characteristic of having a fractional electric charge, unlike the proton and electron, which have integer charges of +1 and -1 respectively." What does the fractional...
  16. S

    Potential ground and electric charge

    In electronics it is customary to define the potential of ground (thinking of the Earth as a large conductor) as zero. Is this consistent with the fact that the Earth has a net electric charge that is not zero?
  17. L

    Compare the distribution of electric charge on the two rods

    Two rods, one brass and the other plastic, have been charged by contact at one end by an ebonite rod rubbed with fur while being supported by an insulator. Compare the distribution of electric charge on the two rods.
  18. Z

    Identifying Electric Charge on Objects

    Homework Statement which quantity of excess electric charge could be found on an object 1) 6.25 x 10 exponenet -19 c 2) 4.80 x 10 exponent -19 c 3) 6.25 elementary charges 4) 1.60 elementary charges Homework Equations i know that 1.60 x 10 exponenet - 19 c is one element charge...
  19. A

    Electric Charge Image Theory - Half-Infinite Planes

    Homework Statement A point charge Q lies along the axis of symmetry between two half-infinite grounded conducting plates which form an angle theta (less than or equal to 90 degrees). a. What are the magnitudes and locations of the image charges? b. What is the total charge on the...
  20. O

    Electric charge on hollow spherical conducting shells Gauss's Law(?)

    There are two spherical hollow conducting shells, one inside the other. The outer shell has a radius 4 times that of the inner shell. There is a switch connecting the two shells, which is for the moment, open. Both shells have a positive charge (inner shell = +20nC and outer shell = +60nC...
  21. M

    Electric charge equally distributed in rice grains

    Homework Statement How many rice grains are needed for an electric charge of a certain strength (I don't remember the value now but is it really relevant?) to be equally distributed amongst them? Homework Equations I hope you can answer that :) The Attempt at a Solution I can...
  22. M

    Electric Field Above a Small Hole in a Charged Spherical Shell?

    Hey. I am trying to solve the following problem: Given a spherical shell with radius a and charge density sigma. If a very small patch of this surface were removed, leaving a small hole, what is the electric field just above and just below this hole? For the electric field below the hole, I...
  23. L

    Electric Charge and Spring Force Problem

    Homework Statement A small sphere with a charge of 2.36 microCulombs is attached to a relaxed horizontal spring whose force constant is 88.6 N/m. The spring extends along the x axis, and the sphere rests on a frictionless surface with its center at the origin. A point charge Q = - 8.55...
  24. M

    Finding q1,q2,q3; Electric charge problem

    Homework Statement Referring to the figure, suppose q_2 is not known. Instead, it is given that q_1+q_2=-1.0. The figure is q1 q2 q3 all lined up in a row with q2 being negative and q1 and q3 being positive as the electric field lines from both q1 and q3 point towards the negatively charged...
  25. R

    What is the Optimal Distance d for Maximum x-Component Force on Charge q?

    Homework Statement Charge Q is on the y-axis a distance a from the origin and charge q is on the x-axis a distance d from the origin. What is the value of d for which the x component of the force on q is the greatest? Homework Equations The Attempt at a Solution
  26. E

    Moving Electric Charge Creating a Magnetic Field

    Does a moving charge create a magnetic field? At first the answer was obvious to me, since I = Q/t then if a charge is moved it is simillar to an electric current, and electric currents create magnetic fields. However in a conductor, an electric current consists of electrons moving past...
  27. N

    How to Calculate Force Between Moving Charged Particles?

    Homework Statement In a frame S, two identical particles with electric charge q move abreast along lines parallel to the x-axis, a distance r apart and with velocity v. Determine the force in S that each exerts on the other, by use of the force law for a uniformly moving charge. I would...
  28. L

    What is the net force on a test charge at the centre of a tridecagon?

    Homework Statement 13 equal charges, q, are situated at the corners of a regular tridecagon. What is the net force on a test charge, Q, situated at the centre. Homework Equations F=k(qQ/r^2) r^ (r^=r vector/r) The Attempt at a Solution The net force will be zero due to the...
  29. D

    Calculating Negative Electric Charge of Oxygen Gas at STP

    Homework Statement Find the negative electric charge of all the electrons in a 56 liter sample of oxygen gas at STP. Assume the oxygen gas is diatomic. Homework Equations The Attempt at a Solution I have no idea. Please help
  30. D

    A question about Electric Charge

    We know that the negative charge on the electron and the positive charge on the proton are equal. Suppose, however, that these magnitudes differ from each other by 0.00007%. With what force would two copper pennies, placed 1.2 m apart, repel each other? Assume that each coin contains 3...
  31. C

    What are some household items capable of gaining an electric charge?

    Hey. I'm just doing a lab an electrostatics and my coursebook suggests a number of materials to use, however, I'm not really getting clear reactions with them. The purpose of the lab is to create an electrostatic series. I first have to establish a reference material; I chose cellophane or...
  32. L

    Question: Does the nuetron have a tiny electric charge?

    I was going through wikipedia and other online 'resource' sites trying to to find an answer to this question, and the answers I came across were difficult for me to interpret. Obviously in general terms the Neutron has a charge of 0 but I remember once reading a few years ago that it might have...
  33. humanino

    Is There a Total Electric Charge for the Universe?

    Dear cosmologists, how do we know the total electric charge of the Universe ? For instance the matter-antimatter asymmetry was a part in (say) 10 billions. But gravity is 40 order of magnitude less intense than electromagnetism, so I need an asymmetry 30 orders of magnitude less for electrical...
  34. G

    Solve "Zero Electric Charge" Homework: x = 51.641 or -3.643

    Homework Statement A charge Q1 = 0.0306 μC is located a distance d = 4.17 cm to the left of another charge Q2 = - 0.0206 μC. a. At what point along the line joining the charges is the electric field zero? Give your answer as the distance x from the charge Q2, positive if the point lies to the...
  35. N

    Electrostatics - Compute the electric charge

    Homework Statement three point charges q1,q2&q3 are place at the vertices of triangle as shown in the diagram charge q1 has been given 4.5 X 10^13 extra electrons, charge q2 given 9.0 X10^13 extra electrons and q3 has had 9.0 X 10^13 electrons taken from it. Calculate the electric charge of...
  36. K

    Line integral ad electric charge

    Homework Statement The force exerted by an electric charge at the origin on a charged particle at point (x,y,z) with position vector r = <x,y,z> is F(r) = Kr / |r|^3 where K is a constant. Find the work done as the particle moves along a straight line from (2,0,0) to (2,1,5). Homework...
  37. N

    Light and electric charge constant?

    Peter Bergmann (a student of Einsteins) in THE RIDDLE OF GRAVITATION, PAGE 60 notes And here I had been thinking only about the speed of light as invarient. Is the above coincidence?? I can't tell... and the space time interval, is also invarient, right?? Are there other entities...
  38. F

    What is the Electric Field of a Uniformly Charged Disk at Different Z Positions?

    Homework Statement A nonconducting disk of radius a lies in the z = 0 plane with its center at the origin. The disk is uniformly charged and has a total charge Q. Find Ez on the z axis at the following positions. (Assume that these distances are exact.) Z = a [__________]Q / (a2εo) - This...
  39. N

    What Is the Final Charge on Sphere C?

    Homework Statement Consider three identical metal spheres, A, B, and C. Sphere A carries a charge of +5q. Sphere B carries a charge of -q. Sphere C carries no net charge. Spheres A and B are touched together and then separated. Sphere C is then touched to Sphere A and then separated from...
  40. L

    Problem in physic of electric charge

    consider a circular clock face of radius= 50cm.a charge of 3nC is placed at the 3 o'clockpoint (a distane of 50cm from the center of the face). a charge of 6nC is placed at the 6 o'clockpoint.9nC is placed at the 9 o'clockpoint and 12nC is placed at the 12 o'clockpoint. what is the electric...
  41. H

    Electric Charge of Water droplet falling

    Homework Statement A charged water droplet of radius 0.02 mm remains stationary in air. If the electric field of the Earth is 100 N/C downward,what is the charge on the water droplet? By comparison with its neutral state, how many electrons must the water droplet have gained or lost? [...
  42. F

    Ponctual electric charge problem

    Hello everyone, my answer on the following problem is wrong and I don't see why. I am translating the question from another language, I am sorry if the english is not clear. Let q1 = 27C localised at x=0, and another charge q2=3C localised at x=1 meters. a)Besides infinity, find a point...
  43. A

    Equilibrium of Charged Particles on an Axis

    Homework Statement The figure below shows charged particle are fixed in place on an axis. In which situation is there a point to the left of the particles where an electron will be in equilibrium? Homework Equations F=\frac{KQ_1Q_2}{r^2}? The Attempt at a Solution The solution says...
  44. C

    Potential for Electric Charge over Spherical Shell using Legendre Functions

    Homework Statement Electric Charge is distributed over a thin spherical shell with a density which varies in proportion to the value of a single function P_l(cos \theta) at any point on the shell. Show, by using the expansions (2.26) and (2.27) and the orthongonality relations for the...
  45. K

    Electric Charge on spheres suspended from an angle

    There is a picture for this question so I will try to describe it to my best ability. Two small spheres, each with mass m=3g and charge q, are suspended from a point by threads of length L=.22m. What is the charge on each sphere if the threads make an angle of 15 degrees with the vertical...
  46. J

    Calculating Net Charge of a Gas with Lost Electrons

    A container holds a gas consisting of 1.75 moles of oxygen molecules. One in a million of these molecules has lost a single electron. What is the net charge of the gas. 1.6 x 10^-19(C/e^-) x n(e^-) So I'm looking for the number of electrons (n) which I think is 1.05625 x 10^19 and...
  47. L

    Electric Charge and Electric Field Problem

    Homework Statement Two small spheres, each of mass 8.00 g , are suspended by light strings 15.0 cm in length (see figure). A uniform electric field is applied in the x direction. The spheres have charges equal to -6*10^-8 and 6*10^-8 Determine the electric field that enables the spheres to...
  48. C

    Deriving Electric Charge: Line, Ring, Cylinder, Cone, Sphere & Shell

    Hi all. I need some help. Without using Gauss's Law, I have to derive the formula for the electric charge for different cases. -I already did few cases such as: 1. Infinite line of charge 2. Semi - infinite line of charge 3. Ring of charge 4. Semi - Ring of charge or any arc of charge 5...
  49. C

    Electrostatics and electric charge and field

    Homework Statement A charged sphere is suspended by a nonconductive string in a uniform horizontal electric field. The electric field exerts a force on the sphere such that its equilibrium position is diplaced at an angle  = 30° relative to the vertical, as shown in the diagram below. The...
  50. P

    How Can A Be Calculated for Uniform Electric Field in a Spherical Shell?

    Homework Statement (Note: Don't worry about significant digits. I just want to be able to do the question and will worry about significant digits on the exam.) In the figure below, a non-conducting spherical shell of inner radius a=2.00cm and outer radius b=2.40cm has (within its...
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