What is Charges: Definition and 1000 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. kartikwat

    Tension in a Circular Loop: Calculations and Free Body Diagram

    The circular loop carrying current experience a tension in external magnetic field.how can this tension be calculated and why doesn't it make a circular motion.
  2. J

    Finding the charge when three charges are in equilibrium

    q1___________Q___________q2 10cm 10cm In the figure above the charge in the middle is Q=-3.1nC. For what charge q1 will charge q2 be in static equilibrium? Relevant equations I think that F=kq1q2/r^2 is relevant my attempt at a solution Since the ions are...
  3. S

    Force of attraction between induced charges

    Homework Statement After induction, the cola can has +ve charges on one end and the -ve charges on the other end. Now when we touch cola can with our hand, why does electrons start flowing through it and get grounded. Doesn't the +ve charges on the one end of the can attract the -ve...
  4. aditya ver.2.0

    How Do Like Charges Exert Force Without Using Energy?

    We all know that energy is required for exerting a pull or push on anything. The amount of energy exerted is proportional to the amount of force exerted and the time period. So if we place 2 like charges near each other, then what energy do they utilize to exert repulsion force on each other.
  5. P

    Electric Field caused by two charges problem

    Homework Statement Two identical point charges, q1 = +2.5 x 10-6 C and q2 = +2.5 x 10-6 C, are placed as shown in the diagram below. Point P is a distance 0.05 m from q1 and 0.12 m from q2, such that the angle at P is 90 degrees. Calculate the magnitude of the Electric field E at point P...
  6. ELB27

    How Fast Do Point Charges Move After Being Released?

    Homework Statement Two positive point charges, ##q_A## and ##q_B## (masses ##m_A## and ##m_B##) are at rest, held together by a massless string of length ##a##. Now the string is cut, and the particles fly off in opposite directions. How fast is each one going, when they are far apart? [from...
  7. ELB27

    Discrepancy in potential of two opposite charges

    Homework Statement Suppose that we changed the right-hand charge in the image attached to -q (instead of +q); what then is the potential at P? What field does that suggest? Compare your answer to Prob. 2.2 [answer written below] and explain carefully any discrepancy. Homework Equations...
  8. A

    Moving Charges and Magnetism Problem

    Homework Statement Two particles A and B having equal charges +6C, after being accelerated through the same potential difference enter a region of uniform magnetic field and describe circular path of radii 2 and 3cm repectively. The ratio of mass of A and B is ______ Homework Equations Force...
  9. schrodingerscat11

    Charge distribution of point charges in spherical coordinates

    Homework Statement Hi! This is not really a problem. I'm just confused on how to express the charge distribution of a set of point charges in spherical coordinates. From our discussion, ρ(\vec{r})=\sum\limits_{i=1}^N q_i δ(\vec{r}-\vec{r}') where \vec{r} is the position of the point where...
  10. N

    An electric dipole consists of a pair of equal but opposite charges

    Homework Statement An electric dipole consists of a pair of equal but opposite charges, +Q and -Q separated by a distance d. What is the electric potential at the point that's midway between these source charges? Through using the formula electric potential = kQ/r, I found the electric...
  11. N

    Why do negative charges spontaneously accelerate when they move to?

    Homework Statement Why do negative charges spontaneously accelerate? The book I am studying from asked me to verify this statement: Negative charges spontaneously accelerate and increase in kinetic energy when they move toward a point of higher potential. I don't understand why...
  12. A

    2 charges and the speed of light

    Consider two equal and opposite charges moving in the same direction and velocity v0, and are separated a distance R. There will always be an attractive electromagnetic force Fel=q2/(4πεR2), but when they are moving, they will produce a magnetic field B=μqv/(4πR2), and thus a repulsive magnetic...
  13. M

    Electric Fields -- Charges at corners of equilateral triangle

    Consider an equilateral triangle of side 15.6 cm. A charge of +2.0uc is placed at one vertex and charges of -4.0C uc each are placed at the other two, as shown in the diagram to the right. Determine the electric field at the centre of the triangle ANgle= 60 sides--> d1= d2=d3=0.156m...
  14. A

    Can Accumulating Charges Be Increased by Placing Machines Underwater?

    I was reading about high voltages machines that accumulate charges and i found out that we can't accumulate much , because eventually the voltage will break down the air near the surface of the sphere ( corona discharge) , what if we put it at the bottom of the sea , where water ( with bigger...
  15. R

    Coulomb interaction not affected by presence of other charges

    One of the observation noted in connection with coulomb interaction is that, it is not affected by the presence of other charges. Why? Thanks.
  16. johann1301

    Can accelerated charges explain the light from a fire?

    I have heard that when charged particles are accelerated, they emit radiation. Combining this with the knowledge that atoms within a fire, are colliding at more then roughly the order of 1021 collisions per second. Is this why fire emits light? Is it the constant high acceleration from the...
  17. A

    Interaction between 2 charges moving at the same velocity

    How does a moving point charge affect another point charge moving at the same velocity and separated by some distance in one direction relative to an observer whom the charge are moving? What formula describes that interaction?
  18. A

    Charges & Insulators: Answers to Questions

    First question i have is about the common glass rod-cloth experiment where the one gets plus charged and the other minus charged.The plus charged item how does it get back the electrons that it missed?If we touch it again with the other one or even through the air?And the minus charged how does...
  19. N

    Charge Batteries with Solar Panel - Questions Answered

    I know it sounds like a really stupid question but i am a bit confused as to what to connect and just want to make sure i do it right. I have a solar panel to charge a set of batteries, i connect the positive wire of the batterie holder to the negative or positive wire for the solar panel, i...
  20. D

    Why don't charges fly off a conductor?

    To be concrete, consider two parallel conducting plates, one positively charged and the other negatively charged. Why doesn't the electric field between the two plates pull the charges off the surface of the two plates?
  21. M

    The energy needed to keep charges in place

    How much energy is needed to place four positive charges, each of magnitude + 5.0mC, at the vertices of a square of side 2.5cm ? I am not entirely sure where to start here. Am I looking for W=? like the work it takes to place it ??
  22. K

    Electric Field with three negative point charges in a line

    Homework Statement Find the magnitude of the electric field this comination of charges produces at point P, which lies 6.00cm from the -2.00μC charge measured perpendicular to the line connecting the three charges. Homework Equations E=k\frac{Q}{r^{2}} F=k\frac{q_{1}q_{2}}{r^{2}}...
  23. M

    How Is the Total Number of Charge Carriers in a Conductor Calculated?

    Homework Statement Let L be the length of the conductor having uniform cross-section area A and density, let I be the current passing through the conductor. How the total number of positive charge carriers in the conductor of length L is (nAL)?
  24. S

    Force from two point charges on a third one

    Homework Statement We have three point charges Q_1, Q_2, Q_3 , forming together an isosceles triangle. Two sides are of equal length r . The point charge Q_1 is located at (0,0), the point charge Q_2 is located at (x_2,0) and The point charge Q_3 is located at (\frac{x_2}{2},\sqrt{r^2 -...
  25. tristanm

    Electric Field from Point Charges

    Homework Statement Two point charges (q1 = -2.6uC and q2 = 8.6uC) are fixed along the x-axis, separated by a distance d = 9.7cm. Point P is located at (x,y) = (d,d) 1. What is Ex(P), the x-component of the electric field produced by q1 and q2 at point P? 2. What is Ey(P), the value of the...
  26. K

    Uniqueness given specified surface charges and voltages

    Suppose we have a collection of conductors for which the voltage is specified on some conductors and the surface charge is specified on others. Is there a coherent way to specify this as a boundary value problem for the voltage (satisfying Laplace's, or in the presence of charge density...
  27. J

    Do Frame Dependent Charges Radiate?

    Let's say there's an electric current in a neutral loop of wire. Then we change to a frame where the loop is moving. That makes the loop an electric dipole, for us. Then somebody shakes one side of the loop, the positive side for example. Do we observe EM-waves? Here's a picture of the loop...
  28. C

    Find the Distance for Net Zero Force: Two Charges at Origin and x=L

    1.)Two charges are fixed in location: charge q1= +8e is located at the origin and charge q2= -2e is located on the x-axis at x=L. At what point can a proton be placed so that it has net zero force acting on it? 2.)F=kq1q2/r^2 3.)I tried to do F=0 K = 8.988 X 10^9 (constant) q1 = (8...
  29. U

    Bound volume and surface charges in dielectric

    Homework Statement Find surface and volume charge densities. Deduce electric field. Homework Equations The Attempt at a Solution Volume charge density: \epsilon_0 \epsilon_r \nabla . \vec E = \rho_f Using ##\vec P = \chi \epsilon_0 \vec E = (\epsilon_r -1)\epsilon_0 \vec E##...
  30. N

    Behaviours of charges inside a conductor(slightly complex scenario?)

    A SPHERICAL conductor in electrostatic equilibrium has no further motion of charges within it. From this, it must imply that there is no net electric field in a conductor and this must necesssarily imply that qenclosed is zero. This is fairly easy to see from Gauss's law: (closed)∫E.dA =...
  31. B

    Calculating Force between Reduced Charges using Coulomb's Law

    Homework Statement What will be the force between two charges if the magnitude of the charges and the distance between them are reduced by 50% Homework Equations F= [(k)(Q1)(Q2)]/(r^2) The Attempt at a Solution Is it that the charge would be 1/2C then 1/2d, then solve for F
  32. Dethrone

    Finding electric field of charges in a rectangle

    Homework Statement Find the electric field of a charge at a corner if there are 4 equal charges at the corner of a rectangle with sides 40 cm and 20 cm. The charges are 2.5 x 10^3 C. Homework Equations E = (kq)/r^2 The Attempt at a Solution I labelled the top left charge q1, the...
  33. H

    Electric potential due to multiple charges

    Hello! For Single Charge: I studied the formula for electric potential for a point charge (V=kq/r). It was derived when the test charge approached the source charge from infinity "head-on". In this case the electric field due to source charge and displacement of test charge were vectors in...
  34. KiNGGeexD

    Two point charges connected by a massless rope

    Question: Two positive charges q(a) and q(b) and masses m(a) and m(b) are at rest, held together by a massless string of length d. Now the string is cut, and the particles fly off in opposite directions. How fast are each going when they are far apart.My attempt: From this the first thing I...
  35. P

    Coulomb's Forces triangle of charges

    Homework Statement Consider the triangle of charges diagrammed below, for which d = 5 cm, q = 2 nC, and the +x-axis points to the right. What is the force Fvec on the 1 nC charge? Give your answer as a magnitude and a direction.Homework Equations F=K(q)(Q)/r^2 The Attempt at a Solution I...
  36. L

    Zero Potential and Electric Intensity in a 2D Plane with 3 Point Charges

    Homework Statement Let us have a square ABCD (D is in the topleft corner) of size 1 m. Let us have 3 point charges situated in points B, C and D. The charges are following QB=2C, QC=-1C and QD=5C. The task is to find (a) the points/plane where the electric potential is zero and (b) two points...
  37. W

    Electric Potential between two charges of equal magnitude

    Homework Statement Two charges of equal magnitude Q are held a distance d apart. Consider only points on the line passing through both charges. If the two charges have the same sign, find the location of all points (if there are any) at which the potential (relative to infinity) is zero. a)...
  38. W

    Conserved Charges of Stress Energy Tensor

    Hello, Hi There I am trying to obtain the relations of the conserved charges of the stress tensor, it has 4, one is the hamiltonian and the other three are the momentum components. \vec{P}=-\int d^3y \sum_i{(-\pi_i(y) \nabla \phi_i(y))} And i have to prove the conmutators...
  39. K

    Effect of dielectric on charges

    What happens To the force between 2 charges if a metal sheet or a dielectric sheet is kept in between the two charges ..(the charges are in vacuum)
  40. S

    What is the electric field at q due to 4 charges in a square configuration?

    http://puu.sh/7MuKv.jpg I'm not sure what equation to apply in this situation. I'm lead to believe Ke((|q1||q2|) / a) Is what I should be applying.The Attempt at a Solution No idea thus far.
  41. L

    Electrical force between charges

    edit: I see that my title is incorrect. This isn't between charges, it is between a charge and a point, sorry about that. The problem: Find the magnitude of the electrostatic force that works on a point 3 meters from q1. q1=3μC My attempts: Feq1=1/(4πε0)*(q1/r) r=3m 1/(4πε0)=8.988x109...
  42. L

    Electric potential halfway between two equal but opposite charges

    I'm having a hard time understanding why the electric potential halfway between two equal but opposite charges is 0. If I put a positive charge halfway between a 5 mC charge and a -5 mC charge, it will accelerate toward the negative charge, but how can it do this if it starts with no potential...
  43. N

    Electric Field strength between 3 charges and directions

    Homework Statement Three point charges lie along a straight line as shown in the figure below, where q1 = 6.36 µC, q2 = 1.57 µC and q3 = −1.82 µC. The separation distances are d1 = 3.00 cm and d2 = 2.00 cm. Calculate the magnitude and direction of the net electric force on each of the...
  44. N

    Electric field strength of 4 charges positioned in a square shape

    Homework Statement Four charged particles are at the corners of a square of side a as shown in the figure below. (Let A = 3, B = 5 and C = 6.) (a) Determine the electric field at the location of charge q. (Use the following as necessary: q, a, and ke.) (b) Determine the total...
  45. E

    How Does Charge Distribution Affect Electric Field and Potential at Point P?

    Homework Statement Two charges of opposite sign and equal magnitude Q = 0.82 C are held 2.0 m apart as shown in the figure. Picture: http://gyazo.com/a78a049ce0a24ad464fd7bb99dffd665 A) Determine the magnitude of the electric field at the point P. B) Determine the electric potential...
  46. applestrudle

    Confused about negative charges in potential field of a pos charge?

    do negative charges in electric fields of positive charges have negative electrostatic potential energy? am I write in thinking they can't be at negative potential (V) because potential is a property of the field and has nothing to do with the charge in the field (like potential energy does)...
  47. L

    Electric field and force between charges at varying distances

    Find the Force and Electric field strength experienced by a 25µC charge particle a distance r away from another 8µC charge particle in air for the following distances. I have this table below would anyone be able to help me out would be much appreciated!
  48. B

    Coulomb's Law (3 charges in equilateral triangle)

    Three charged particles are placed at the corners of an equilateral triangle of side L = 1.74 m. The charges are q1 = 3.63 µC, q2 = −8.05 µC, and q3 = −6.31 µC. Calculate the magnitude and direction (counterclockwise from the positive x axis) of the net force on q1 due to the other two...
  49. ShayanJ

    Point charges and multipole expansion

    Consider the following charge distribution:A positive charge of magnitude Q is at the origin and there is a charge -Q on each of the x,y and z axes a distance d from the origin. I want to expand the potential of this charge distribution using spherical coordinates.Here's how I did it...
  50. Saitama

    Breaking the chain of charges

    Homework Statement Homework Equations The Attempt at a Solution I am not sure how to proceed with the given problem. I can write down the net force on any of the charges but what should be the condition that the chain breaks? :confused: Any help is appreciated. Thanks!
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