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. D

    Electric potential between two point charges

    Homework Statement Two point charges are separated by a distance r. If the separation is reduced by a factor of 3/2, by what factor does the electric potential between them change? A. 3/2 B. 2/3 C. 9/4 D. 4/9 E. Sqrt(3/2) Homework Equations The Attempt at a Solution Honestly I...
  2. A

    Coulomb's Law with 3 Point Charges

    Homework Statement The questions asks to consider the following comment about a situation where there are three point charges held fixed along a linear line. "There will be zero net electric force on the charge in the middle due to the other charges. Using Coulomb's law, the force due to...
  3. Roodles01

    Forces on symmetrical electrostatic charges

    Homework Statement 3 point charges L(-b, b) M(b, b) & N(0, 0) have charges Q, -3Q & Q. I need to find the force on the charge at the origin. Homework Equations Coulomb's Law important, here. F = 1/4∏0 q^2/r^2 r(hat) z-component no existent (from coordinates given) x- & y-components to...
  4. S

    What is the electric potential midway between the two charges?

    Homework Statement Consider two equal positive charges (q=+2.0 µC) a distance of 3.0 cm apart. What is the electric potential midway between the two charges? What is the E field at this point? I got the work and everything all solved out, i just don't know where some of the numbers came...
  5. R

    Does Coulomb's Law apply to more than point charges?

    I read an article on Coulomb's law which read, ''Coulomb's law only applies to point charges'' (or something along those lines). Am I wrong, or is there an equivalent that can work for magnets/big electric charges?
  6. O

    Any components to determine the charges?

    I would like to make an electronic electroscopes based on following concept, but its design cannot determine whether the charges are positive or negative. Does anyone have any suggestions what kind of components I can add into this device to determine the charges? Thanks in advance for any...
  7. T

    How do we arrive at Q = -1 from T3 and Y?

    Im reading Peskin&Schroeder, chapter 20, the one that describes the Standard Model. I got the general idea, symmetry breakings and so on, but I am getting quite confused when starting to go to the first mathematical details. My doubts are when, in eq 20.69 defines Q=T3+Y and then forces that...
  8. B

    Electric Fields and point charges

    Homework Statement A point charge −3 pC is concentric with two spherical conducting thick shells, as show in the figure below. The smaller spherical conducting shell has a net charge of 22 pC and the larger spherical conducting shell has a net charge of 18 pC. 1-4)Answer in units of...
  9. S

    Electric field and potential of 2 point charges

    Homework Statement A -2 μC charge and a 10μC charge are separated by 15.0cm. At what point is the electric field zero? At what point is the electric potential zero? Homework Equations E=(kq1/r1^2)+(kq2/r2^2) V=kq1/r1 + kq2/r2 The Attempt at a Solution My main problem is with...
  10. G

    Force (potential, I think) to Kinetic Energy - Two charges

    Two particles each have a mass of 7.7 x 10-5 kg. One has a charge of +5.9 x 10-6 C, and the other has a charge of -5.9 x 10-6 C. They are initially held at rest at a distance of 0.91 m apart. Both are then released and accelerate toward each other. How fast is each particle moving when the...
  11. C

    How Do You Calculate Equilibrium Position Between Charges Using Coulomb's Law?

    Coloumbs Law & Charges. Please help! :( Homework Statement A charge of +2.0 nC and a charge of +8.0 nC are separated by 36.0 cm. Find the equilibrium position for a −2.0 nC charge as a distance from the first charge. Answer in units of cmHomework Equations q/r^2 The Attempt at a Solution I...
  12. B

    Electric field of two point charges

    Homework Statement Two point charges Q and -Q are separated by a distance d. The point p forms an equilateral triangle with the two charges of side length d. Find the magnitude and direction of the electric field at point p. What is the electric potential at P? Then, a charge of 2Q is placed...
  13. M

    Calculating Flow Around Elliptical Cylinder w/ Point Charges

    Hey all, I am using the Joukowski transform to calculate the electrostatic potential and streamlines around an elliptical cylinder. The flow is caused by two point charges (one positive, one negative). My idea was, of course, to first solve the problem for a circular cylinder, and then...
  14. J

    What Is the Ratio of Charges q2 to q1 Based on Their Electric Field Angles?

    Homework Statement The drawing shows two positive charges q1 and q2 fixed to a circle. At the center of the circle they produce a net electric field that makes an angle 28.6° with the vertical axis, measured counterclockwise. Determine the ratio q2/q1. [the drawing shows a circle with two...
  15. tom.stoer

    Radiation of free falling charges and charges at rest in a static gravitational field

    The question is rather old but I am not sure if we have a final conclusive answer (I was not able to figure it out for myself, nor have I found consensus in the literature) 1) do free-falling charges in a static gravitational field radiate? 2) do charges at rest in a static gravitational...
  16. A

    Electric Potential Energy: Work Required to Move 3 Charges Out to Infinity

    Homework Statement Three charges are distributed as follows: http://tinypic.com/r/1fviq0/5 How much work must an external force do to move them infinitely far from each other? Homework Equations W = -\DeltaU = (kq_{1}q_{2})/r The Attempt at a Solution So what I did was find...
  17. B

    Find all the points along the line passing through both charges

    Homework Statement For each of the following arrangements of two point charges, find all the points along the line passing through both charges for which the electric potential V is zero (take V = 0 infinitely far from the charges) and for which the electric field E is zero. (Use the...
  18. O

    What kind of charges is within the smoke from cigarette?

    Positive or negative charges? Does anyone have any suggestions? Thanks in advance for any suggestions
  19. D

    Speed at which two charges collide

    Homework Statement Point charge A of mass m for which q=-Q is held in place as point charge B of mass m for which q=+Q is released from rest at a distance x. What is the speed of charge B as it collides with charge a? (This isn't an actual problem we have, just something that I was wondering...
  20. G

    Electromagnetism : work done in assembling free charges to a distribution of charges

    Homework Statement Consider a system of “free” charges {qi } and “bound” charges {Qi }. Both types of charges feel the Coulomb force due to all other charges (free and bound). However, the bound charges feel additional “mechanical” forces due to the other bound charges. Let the mechanical...
  21. Gliese123

    Balancing Charges & Electrons in Cr3++CIO3-+H2O → Cr2O72-+Cl-+H+

    Homework Statement Hi. :) I'm supposed to balance the formula and write the values. Cr3++CIO3-+H2O → Cr2O72-+Cl-+H+ Specify:Amount of electrons and: Charges The Attempt at a Solution I don't really got any clue. Please help! Cr3+ have +3 The oxygen have -2 and then? Cr3++CIO3-+H2O →...
  22. G

    Electric Force Calculation with Two Point Charges on Axis - Step by Step Guide

    HELP I don't understand at all Homework Statement Two positive point charges on the y-axis, each of which has a charge of 5.0 10-9 C, are located at y = +0.60 m and y = -0.60 m. Find the magnitude and direction of the resultant electric force acting on a charge of 7.6 10-9 C located at x =...
  23. G

    Electric field stregth between charges

    1. What is the magnitude and direction of the electric field strength midway between a +60uC charge and a -30uC charge, if the charges are 2.0m apart? 2.E=kQ/r^2 3. E1=Kx-30u/1 E2=-2.75x10^5 E2=kx60u/1 E2=5.4x10^5 Etotal=E1 + E2 ----> 2.7x10^5 N/C towards the - charge (my book says i have...
  24. K

    Three negative point charges lie along a line

    Three negative point charges lie along a line as shown in the figure. figure: http://tinyurl.com/7xppvc8 Find the magnitude and direction of the electric field this combination of charges produces at point , which lies 6.00 from the charge measured perpendicular to the line connecting the...
  25. J

    What Is the Electric Potential at the Origin Given Four Point Charges?

    Homework Statement 4 charges, distributed as follows 12*10^{-6} C @ (-4,4) 12*10^{-6} C @ (4,4) -6*10^{-6} C @ (-4,-4) -3*10^{-6} C @ (4,-4) Calculate the potential at the origin if the potential at infinity is zero. Homework Equations V= U/q = -W/q = ∫E*dl = k*q/r...
  26. phosgene

    Work done moving two charges together

    Homework Statement Two point charges of magnitude +10 μC each are placed 0.2 m away from each other. a) How much work is done in placing the second charge? b) Is there any point at which the electric field and electric potential are both 0? Homework Equations Work = (charge of first...
  27. M

    Where an electric field is equal due to two charges?

    Hey there! I don't understand how this really works. With each region, how is it that the charges carry over...? The answer is the fourth region. I'm just totally lost, please explain to me. :)
  28. N

    Solving for Electric Force: Two Point Charges

    Homework Statement Two point charges, 3q and q lie along x-axes. 3q is at 0.00 m and q is at 3.0m. Find the point between the 2 charges at which the net force on charge q is zero. Homework Equations F=kq1q2/r^2 The Attempt at a Solution Really can't figure this one out. Missed the...
  29. R

    Two charges are placed at the corners of a square

    Electric Potential ! Homework Statement Two charges are placed at the corners of a square. One charge, 4.0μC, is fixed to one corner and another, -6.0μC, is fixed to the opposite corner. What charge would need to be placed at the intersection of the diagonals of the square in order to make...
  30. G

    Electrostatics problem: solve for where E=0 given a configuration of charges

    Hey everyone, thanks for taking a look at this. I was hoping you could look over this to make sure I solved this correctly. Thanks for you time. Homework Statement ---- "+" ---- "+" ---- "-" ---- Given this configuration of charges where the plus and minus indicate the magnitude of...
  31. D

    Problem With Repulsive Charges

    Homework Statement Two 3.0g spheres on 1.0m-long threads repel each other after being equally charged, as shown in the figure. Homework Equations F = k*q1*q2/r2 The Attempt at a Solution sin 70° = Ty/T T = (m*g)/sin 70° T = 0.003*9.81/sin 70° T = 0.03132 N Tx = T*cos 70° Tx =...
  32. M

    Finding Charges: Electric Force & Polystyrene Foam

    Homework Statement Two balls of polystyrene foam are about 4 cm from each other and repel with an electric force of 0.2 N. Find the values of the two charges knowing that one of the balls has a charge that is twice the other.Homework Equations F= (kq1q2)/r2The Attempt at a Solution F=...
  33. M

    Using 5 point charges, finding the charge of q1 and q2 using given force

    Homework Statement The figure shows five point charges placed on a line, at intervals of 1 cm. For what values of q1 and q2resultant electrical force exerted on each of the three charges is zero? Homework Equations I imagine the law of coulomb is used here, however, I'm not sure how I'm...
  34. P

    Electric Force of Two Charges on Third Charge

    Homework Statement 1. Charge q1= 1.00*10^-9C is located +0.01 m from the origin along the x-axis. Charge q2= 2.00*10^-9C is located +0.03 m from the origin. What is the electric force exerted by these two charges on a third charge, q3= 1.5*10^-9C, located at the origin? a. 1.65*10^-4N...
  35. K

    Placing charges with coulomb's law problem

    Problem: a charge +Q is located at the origin and a second charge, +4Q is at a distance d on the x-axis. where should a third charge, q, be placed, and what should be its sign and magnitude, so that all three charges will be in equilibrium. attempt: I don't know how to solve it fully, but...
  36. T

    Velocity of two equal charges placed by one another

    Homework Statement Two identical 8.5 point charges are initially 4.5 from each other. If they are released at the same instant from rest, how fast will each be moving when they are very far away from each other? Assume they have identical masses of 2.0 . Homework Equations...
  37. S

    Find Net Force Neutral Point b/w Q1 & Q2 Charges

    Homework Statement A charge, Q2 = -7.00x10^-6 C, is 8.00 cm to the right of charge Q1 = 6.00x10^-6 C. Where can a third charge be placed, along the line connecting Q1 and Q2, such that it experiences no net force? Give distances relative to Q1 and use a plus sign if the third charge is to the...
  38. K

    Relativistic corrections to E-fields of charges bounded inside a Gaussian surface

    If I have a spread of electrical charges contained inside a Gaussian surface, and if I cause those electrical charges to move at relativistic speeds, the electric fields of those charges should be subject to relativistic contraction. What happens then to electric flux that cuts through that...
  39. G

    Net Charge Calculation Help

    Homework Statement Calculate the net charge on a substance consisting of a combination of 5.4 1013 protons and 4.2 1013 electrons. Homework Equations I subtracted the two but i still had the wrong answer The Attempt at a Solution 9.6E13 1.2E13
  40. G

    Electric Force Between +2.8 µC & -4.8 µC: Calculate Now

    Homework Statement What is the electric force between a glass ball that has +2.8 µC of charge and a rubber ball that has -4.8 µC of charge when they are separated by a distance of 4.5 cm? Homework Equations F=k*Q1*Q2/r^2 The Attempt at a Solution -59.6507 -8.8888888.889 4.4380e12
  41. G

    Finding the electric field at 3 points due to 2 identical charges.

    3 points (a,b and c) and two identical positive charges. How do you find MAGNITUDE of the electric field at the 3 points? I just need to rank them, don't need numbers. all points are on the x-axis: A (x=0); charge +Q(x=1); B (x=3); c(x=4); charge+Q(x=5) (Picture attached in the 3rd post)...
  42. C

    Electric Field of Three Point Charges

    Homework Statement Three point charges lie along a circle of radius r at angles of 30°, 150°, and 270° as shown in the figure below. Find a symbolic expression for the resultant electric field at the center of the circle. Homework Equations \vec{E}=\frac{k_{e}q}{r^{2}} The Attempt at a...
  43. O

    Charges, Electric Fields, and Work?

    Homework Statement a +70µC charge is placed 50 cm from a -50µC charge. How much work would be required to move a -.5µC test charge from a point 10 cm from the +70µC charge to a point 20 cm from the -50µC charge? Homework Equations F=k(q_{1}q_{2}/r^{2}) PE=Fd ...that's all I could get...
  44. D

    Static equilibrium for three point charges

    The result I got seemed sort of messy and I'm not sure I've gotten the basic idea correctly, so I thought I'd make it sure. I think this was the easiest problem we had to solve for charge distributions and point charges and whatnot, so I know for sure I'll have to practice more if I made any big...
  45. J

    Coulomb's law point charges distance for 0 net force

    Homework Statement One charge of (+5µC) is placed in the air at exactly x = 0, and a second charge (+7µC) at x = 100cm. where can the third charge be placed so as to experience zero net force due to the other charges? Homework Equations F=KQ1Q2 / D^2 The Attempt at a Solution Q1 =...
  46. P

    Two Charges - Electric Potential Question

    Homework Statement Two charges q = 4.0μ C are fixed in space a distance d = 4.0 cm apart, as shown in the figure. With V = 0 at infinity, what is the electric potential at point C? You bring a third charge q = 4.0μC from infinity to C. How much work must you do? What is the potential...
  47. J

    Generating Noether charges for Dirac Lagrangian

    I have been calculating the currents and associated Noether charges for Lorentz transformations of the Dirac Lagrangian. Up to some spacetime signature dependent overall signs I get for the currents expressions in agreement with Eq. (5.74) in http://staff.science.uva.nl/~jsmit/qft07.pdf . What...
  48. E

    Question about the motion charges moving within an electric field

    I've almost certain that I have read/ seen from MIT's OCW that the motion of a charge within an electric field does not follow the field lines. Today my physics teacher said the opposite, that the path of motion of a charge within a field will follow a field line. Who is right? And why? EDIT...
  49. H

    Magnetic Forces on Conductors and charges- the motor principle

    Magnetic Forces on Conductors and charges-- the motor principle An electron moving through an electric field of 475 V/m and a magnetic field of 0.1T experiences no force. if the electron's direction and the directions of the electric and magnetic fields are all mutually perpendicular, what is...
  50. L

    Electric field in stored charges

    Okay, say we have one positive point charge, and one negative point charge. Their charge values are exactly opposite (q and -q). And say we place them a certain distance apart and hold them there, maybe creating something like a point-charge capacitor. These point charges can hold and transfer...
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