Electric charges Definition and 86 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

    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...
  2. 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...
  3. 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!
  4. S

    Electric Charges Homework: Potential Difference & Capacitance

    Homework Statement Two parallel conducting plates, separated by a distance d, are connected to a battery of emf \epsilon. Which of the following is correct if the plate separation is doubled while the battery remains connected? a. The electric charge on the plates is doubled. b. The electric...
  5. J

    Electric Charges: Calculating Charge q for Ink Drops

    Homework Statement In an inkjet printer, letters and images are created by squirting drops of ink horizontally at a sheet of paper from a rapidly moving nozzle. The pattern on the paper is controlled by an electrostatic valve that determines at each nozzle position whether ink is squirted...
  6. I

    Question about distribution of electric charges on two parallel plates

    Here is a problem I made up, in order to try to understand electrostatics of conductors better. Suppose two large square parallel conducting plates, are in space. One has a charge of Q, and another has a charge of -q. They are put close together, from a separation of L, to a separation of l...
  7. S

    Final Net Charge for +23.62µC & 12.82 x 10^{14} Electrons

    Homework Statement An item starts with a net positive charge of +23.62µC. A total of 12.82 x 10^{14} electrons are transferred to the object. What is the final net charge? a. +228.7µC b. -181.5µC c. -25.67µC d. +181.5µC Homework Equations q=neThe Attempt at a Solution I'm...
  8. K

    Another Electric Charges Q about Leaves

    Homework Statement set up:(they three are all connected) l (referred to as top) /\ (the bottom two called "leaves") - two leaves are separated when negatively charged rod touches the top of the (vertical thing that connects the two leaves at the bottom) - when rod is taken...
  9. S

    Electric Charges: Balancing Electrostatic & Gravitational Forces

    Homework Statement An electron is in a vacuum near the surface of the Earth. Where should a second electron be placed so that the electrostatic force it exerts on the first electron balances the gravitational force on the first electron due to Earth ? Homework Equations The Attempt...
  10. R

    Electric Shock During Sleep: Is It Possible to Be Zapped by Your Own Body?

    hey everybody! i have an inquiry!...Why? and How?? people get "charged" and get self electrically shock or electroshock somebody else?... let me explain myself better...for example...my mom has like 2 weeks that she gets "charged" electrically...everytime she touches something she gets...
  11. K

    How Do You Determine the Magnitude of Electric Charges on the X-axis?

    Given three charges fixed along the x-axis and their length from the origin, how do I find their magnitude in C's?
  12. S

    Finding a point midway between two electric charges

    Homework Statement Two point charges of magnitude 2nC and -4nC are separated by 35 cm. The Coulomb constant is 8.98755e9 Newtons (Meters squared/ Coulombs squared). What is the potential difference between a point infinitely far away and a point midway between the charges? R= .175Homework...
  13. K

    Electric charges and large bodies

    According to my book the electric charge of large bodies like the Earth and the moon is pretty close to zero. But the Earth has poles and a magnetic field, which suggests that it isn't uniformly distributed at all. These two things SEEM contradictory to me, what is it that I am not getting? k
  14. S

    Where are the points?Where are the points?

    Homework Statement A 10.0 nC charge is located at position (x, y) = (1.0 cm, 2.0 cm). At what (x, y) position(s) is the electric field a. -225,000i N/C b. (161,000i + 80,500j) N/C c. (28,800i + 21,600j) N/C Homework Equations E = (1/4\pi\epsilon)(q/r^2) F = Kq_1q_2/r^2 The...
  15. Y

    Electric Charges: Forces on A and C Explained

    Homework Statement Two equally charged identical conducting spheres, A and B, repel each other with a force of 2.0 x 10^5 Newton. Another identical uncharged sphere, C, is touched to A and then moved over right next to B. What is the electric force on A now? What is the electric force on C...
  16. R

    Electric Field of Two Point Charges on the x-axis

    Two point charges, q1 = 4.0×10-6 C and q2 = -1.0×10-6 C, are located on the x-axis at x1 = -1.0 cm and x2 = 3.0 cm. (a) Determine the electric field at the origin. (b) Determine the x coordinate of a point on the positive x-axis where the electric field is zero; i.e., a test charge...
  17. J

    Can a Grounded Person's Brain Still Generate Electric Charges?

    As far as I know, the brain generates electric pulses to communicate. If a human being is electrically grounded, how could the charge flow or get created in his brain? A grounded man shold be brain dead :), right?
  18. F

    Electric Charges (Quick Question)

    Can some one please explain to me why charged particles attract neutral ones, yet if you place the numbers into the equation Ep=-kQq/r, it will show you that there is no potential energy between a charged particle and a neutral one, because one of the Q's will be 0. How does this make sense...
  19. F

    Electric Charges Homework: Find Where Electric Field & Potential Equal 0

    Homework Statement A +10mC charge is placed 0.20 m from a -2.0mC charge. Where on the line joining the 2 charges is the a) electric field equal to zero? b) electric potential equal to zero? Homework Equations The Attempt at a Solution I am not sure, but I think that the answer to...
  20. H

    Electric charges moving and magnetic field

    I know that a current creates a magnetic field and so do moving electric charges. My question is how fast a single charge moves so that it will create a magnetic field. Should its velocity be around c to make that? Thks
  21. K

    Calculate Electric Field Magnitude at x=0.5, y=0.5

    Two electric charges, q1 = +22.8 nC and q2 = +10.1 nC, are located on the x−axis at x = 0 m and x = 1.00 m, respectively. What is the magnitude of the electric field at the point x = 0.50 m, y = 0.50 m? I used the equation E= ((k)(q))/r^2 for each q1 and q2. I don't know what to...
  22. S

    Electric Charges: Opposite Attract, Same Repel

    Why do electric charges of opposite sign attract each other but charges of the same sign repel each other?
  23. J

    Electric Force: Find Point of Zero Charge on X-Axis

    can someone help me on this? thanks in advance: A positive charge +2q lies on the x-axis at x=-a and a charge -q at x=+a. Find a point where the electric force on the third charge Q would be zero. should i continue on using Coulomb's Law, and just use arbitrary variables or is there...
  24. V

    Electric charges and force (tricky test question)

    On my physics test yesterday, one of the questions was the following: At a particular point in space, a charge Q experiences no force. It follows that A. if charges are nearby, the total positive charge must equal the total negative charge. B. there is not enough information to...
  25. P

    Massless Charged Particles: Fact or Fiction?

    I've been studying the Yang-Mills theory, which predicted the existence of massless charged particles. That theory was later proven to be wrong, but it made me wonder nevertheless - can there ever be massless charged particles? And if such particle exists, how will it behave? How will it...
  26. D

    How Many Electrons Are Needed to Levitate a Person?

    A small metal plate is bolted to the ceiling, and an "electron pump" is connected between the metal plate and yourself (mass of 60 kg). The pump starts pumping electrons from the metal plate to you. How many electrons must be moved from the metal plate to you in order for you to hang suspended...
  27. S

    Proving SHM in a System of Electric Charges

    Two postitive charges +Q are held at fixed distance d from each other. A particle of charge -q is placed at the mid point between them and given a small displacement y, on the line perpendicular to the line joining them and released. Show that hte particle described SHM of period...
  28. zoobyshoe

    Electric Charges Scatter Light

    Reading about the double slit experiment in Six Easy Pieces I came across something I had questions about, which is how they detect whether an electron has gone through one slit or the other: "To our electron apparatus we add a very strong light source, placed behind the wall and between the...
  29. N

    REally confused Need Help on electric charges and Coulomb's Law

    Electric Charges and Coulomb’s Law Guys, help me solve these problems. I'm really in big trouble.. thanks guys! a)Two charges of equal magnitude exert an attractive force of 4.0x10-4 N on each other. If the magnitude of each charge is 2.0μC, how far apart are the charge? b)Three equal...
  30. X

    How to Calculate Potential and Speed of a Proton Near a Barium Nucleus?

    A barium nucleus has a charge of q = +56e (where e is the proton charge). a. find the potential V at a radius of 10-12 m from the Nucleus. If a Proton is released from this point, how fast will it be moving when it is 1 m from the nucleus? Note: Assume V (infinity=0) Any help?
  31. P

    Coulombs Law and Electric Charges

    Likewise, this similar problem also has me stumped A charge of 7.00 mC is placed at each corner of a square 0.80 m on a side. Determine the magnitude of the force on each charge. Any help would be greatly appreciated!
  32. S

    Deriving V-E Relation for Uniformly Charged Rod at Radial Distance r > a"

    Could someone help me out on this problem? Derive a relation between the potential V and the magnitude of the Field E at a radial distance r from the axis of a very long uniformly charged rod of radius a ( r > a ).
  33. S

    Electric Charges: Solving a Half Sphere Problem

    Hello, I need some guidance. This is the problem: Imagine that we have a half sphere (hemishpere) that is hollow with a charge of +q distributed evenly across the inside of the "bowl". What is the electric field due to this charge at point P? I have attached an image to help visualize this...
  34. M

    Clueless about electric charges questions;

    Oh boy, for some reason I'm just not getting this. I must be fouling up some really simple part. He just dives into problems without explaining the derivations and uses of the problems. Forgive my lack of knowledge on use of units. My questions: "A uniform line charge extends from x =...
  35. M

    Electric Field at Point C: A to B & B to C

    Charge A is +2.5*10^-5C Charge B is -3.7*10^-7C. A is 25cm away from B. Point C is 10cm away from point B. What is the electric field at C? All points are in a line A--B-C.
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