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.

View More On Wikipedia.org
  1. G

    How to calculate velocity from the attraction of two charges

    I need to calculate the acceleration of an proton to a metal plate with a charge of 16 Coulombs(negative charge), 1 meter away. Then I need to calculate the velocity at the moment it passes the plate. Starting Velocity is 0 m/s. What is the velocity and what is the acceleration? This is not...
  2. S

    Magnetic field of moving charges

    Hi! I wonder if there was any experimental measurement of magnetic field produced by mechanically moving charges. In principle the equation is well known. (1) But is there any experimental proof of this equation? I know it can be reformulated into this. (2) My question is "Is there any...
  3. moenste

    How many electron charges are there on the drop? (Millikan)

    Homework Statement In a measurement of the electron charge by Millikan's method, a potential difference of 1.5 kV can be applied between horizontal parallel metal plates 12 mm apart. With the field switched off, a drop of oil of mass 10-14 kg is observed to fall with constant velocity 400 μm...
  4. O

    Charges of three long charged cylinders centered on 1 axis

    The figure shows a section of three long charged cylinders centered on the same axis. Central cylinder A has a uniform charge qA= +3q0. What are the charges of qb and qc if E is 0 on point > a) 1 ( between A & B ) b) 2 ( between B & C ) c) 3 ( out side the cylinders ) My solutions were based on...
  5. P

    How can we talk about charges very close to zero?

    I was reading about the definition of electric field. It said that electric field at a point due to a source charge is the force exerted by it on another charge placed at that point divided by the magnitude of charge placed at that point. But, obviously, if we place any finite charge in electric...
  6. N

    Is it possible for opposite charges to repel each other?

    Homework Statement From rest, how fast would two particles be going at the instant they collide ( if they attract) or when they're infinitely far apart (if they repel)? Explain carefully. Particle A: 3nC Particle B: -4nC Each has a mass of 7 mg. They are .05 m apart. Homework Equations ΔK +...
  7. N

    Finding the velocity of two charges

    Homework Statement If two particles were allowed to move freely, how fast would they be going at the instant they collide or when they're infinitely far apart? Explain Carefully. There are no initial velocities given. The charges are -4 nC and 3 nC and each has a mass of 7 mg. Homework...
  8. thecourtholio

    Interaction Energy For Two Point Charges

    Homework Statement Find the interaction energy ( ##\epsilon_0 \int \vec{E_1}\cdot\vec{E_2}d\tau##) for two point charges, ##q_1## and ##q_2##, a distance ##a## apart. [Hint: put ##q_1## at the origin and ##q_2## on the z axis; use spherical coordinates, and do the ##r## integral first.]Homework...
  9. Blockade

    Is the total electric field of two opposite charges 0?

    Let's say you have two particles that are the same in magnitude but have opposite charges like the equation down below: E1 = -q*k/r^2 E2 = q*k/r^2 ETotal = q*k/r^2 + -q*k/r^2 = 0 Does this mean that the electric field of both these charges cancel out each other? Then what is the electric...
  10. A

    Coulombs law and particle charges

    Homework Statement An electron and another particle experience an attractive force of 0.0096 N when they are 0.001m apart. what is the charge of the other particle q1= -1.602E-19 F=-0.0096 r=0.001 2. Relevant equation how do you find q2 out to solve the equation The Attempt at a Solution
  11. I

    Find the distance between the q charges

    Homework Statement Two 3.2 g point charges on 1.0-m-long threads repel each other after being equally charged, as shown in the figure.(https://session.masteringphysics.com/problemAsset/1384363/9/25_P59_sf=2.jpg) [Moderator note: Added back the Problem Statement header and inserted the figure...
  12. akashpandey

    B From where electron and proton get there charges?

    I want to know what is the source of electron and proton get their charge ?
  13. AmKo3

    B Centre of Charges Coincide & Dipole Moment: Explained

    What does it mean when we say "centre of charges coincide"? What is the physical meaning of dipole moment?
  14. P

    Jackson 3.7 Three point charges (q,−2q,q) are located in ....

    Homework Statement Hi, The question is " Three point charges (q,−2q,q) are located in a straight line with separation a and with the middle charge (−2q) at the origin of a grounded conducting spherical shell of radius b ..." I have found a solution for this problem but there is one step that...
  15. H

    Two equal positive charges are held fixed and separated by d

    Homework Statement Two equal positive charges are held fixed and separated by distance D. Find the electric field vector along their perpendicular bisector. Then find the position relative to their center where the field is a maximum There was another thread with this question but the...
  16. N

    Modeling an electric circuit by tracking individual charges

    Hello, Given a simple electric circuit like the one below (taken from Wikipedia) If we were to start from tracking all the forces acting on each individual free electron in the circuit, would it be possible to eventually find all the currents and voltages acting in the circuit? Probably a...
  17. G

    Image Charges Purcell Discussion

    Hi everyone, I have a question (or three) regarding Purcell's discussion of image charges, in pg 137-139 of the third edition of his EM book. He goes over the classic image charge example: a plane held at zero potential, and a charge Q a distance h above it. I'm fine with everything he...
  18. J

    Find the unknown charges q1 and q2

    Homework Statement The geometrical positions of point-like charges and point A situated in the xy-plane in terms of the length parameter a. The vector of electric field E at point A is shown schematically and measured as E = Exi + Eyj (that is, both Ex and Ey are given). If possible, find the...
  19. B

    Introducing Local Charge to Conductors?

    Homework Statement Is it possible to introduce local charge on a conductor? Homework Equations - The Attempt at a Solution I know that electrons can move freely from atom to atom in the conductor, so if you introduce excess electrons to the conductor, they'll spread out and there won't be a...
  20. Behrouz

    What are the charges of quarks and leptons?

    Hello everyone, I'm sorry if it's a dumb question, I'm very new in self studying particle physics. May I ask when we associate a charge (i.e. positive or negative) to quark and lepton, is it only because of their attraction or repulsion toward each other? in other words, is it just to name one...
  21. Surya97

    I Electric and Magnetic Fields, Photons, Charges

    I know that magnetic fields create moving charges (an electric current) normal to the plane of the magnetic force lines. I also have heard that magnetic and electric fields create each other in a perpendicular direction to the other (badly worded). Electric currents are moving charges (usually...
  22. W

    Oscillating charges in an electric field

    I don't have a single problem, my teachers use this a lot. a few examples, are an uniformely charged circle and a point charge in the middle, where if you move the point charge a small distance perpendicular to the circle, it would begin to oscilate, and i need to find the frequency of...
  23. G

    I Discrepancy in Co-Moving Charges Magnetic Force?

    Consider two identical charges separated by some distance. Both are moving together with the same velocity, and the velocity vectors are perpendicular to a straight line drawn between the charges. Each charge has charge q, speed v and they are separated by a distance of r. In the rest frame of...
  24. SSGD

    Light Momentum Transfer between point charges

    Hi, I am trying to understand how light momentum transfers between point charges. I have a few questions if you could help me find some answers or direct me to some sources. Situation #1 Electron/Wire - There is an electron at rest light years away from a wire that has AC flowing thru it...
  25. P

    Constant Charge/Current Densities with Accelerating Charges

    In classical physics, when electric charges accelerate, they are expected to radiate. Electromagnetic waves, are by their nature the result of changing electric and magnetic fields. But is it possible to have acceleration of charges without having changing electric and magnetic fields? One...
  26. G

    Question about Electric Fields and Charges

    Homework Statement So I was given some questions as practice, and I can't seem to do them. Here is a link to the questions: http://i.imgur.com/ZmkqCAV.jpg (the answers are in square brackets) Ive only been able to calculate Q3 and Q2 so far. I would really especially like help with Q1. I've...
  27. S

    B Question about understanding conductors for EM course

    So in conductors, the electrons will distribute themselves to the surface via repulsion forces. But why do we say that the electric field inside is zero? If I put a positive charge inside, clearly it will move in some direction from the electric field of generated from the electrons. Also, are...
  28. C

    Electric field strength at a point between charges

    Homework Statement A +1.0 μC charge is placed at point X. A +4.0 μC charge is placed at point Y, 50 cm from X. How far from X, on the line XY, is the point where the electric field strength is zero? Homework Equations E = Q/4πε0r2 The Attempt at a Solution I know that the electric field is...
  29. G

    Coloumbs Law when have 3 charges at unknown distances

    Homework Statement I have a question that I can't figure out. Question is "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 (other than infinitely away) can a proton (a unit positive charge e) be...
  30. UMath1

    Kinetic Energy of two positive charges flying apart

    Usually when we calculate the kinetic energy acquired by a positive charge as it moves in the direction of the electric field produced by another positive charge, we assume that the source charge remains stationary and so the loss in potential energy for the moving charge is equal to its gain in...
  31. P

    Components of force of 2 moving charges

    Homework Statement A particle with charge ##e## and position vector ##\vec{r}## (relative to some frame, S) moves with constant velocity ##\vec{v}##. A second charge ##e'## is moving with the same velocity ##\vec{v}## through the field generated by ##e##. If ##\vec{d}## is a vector from ##e##...
  32. Kernul

    Electric Field in all of space from charges along the Z-axis

    Homework Statement A charge is distributed evenly along the ##z## axis with a density ##\lambda = 3 \frac{\mu C}{m}##. There is also a cylinder with radius ##r = 2## and on his side there is a superficial density charge of ##\sigma = -\left( \frac{1.5}{4 \pi} \right) \frac{\mu C}{m^2}##. Both...
  33. S

    Conserved Noether charges for Lorentz symmetry of the action

    Homework Statement Consider the infinitesimal form of the Lorentz tranformation: ##x^{\mu} \rightarrow x^{\mu}+{\omega^{\mu}}_{\nu}x^{\nu}##. Show that a scalar field transforms as ##\phi(x) \rightarrow \phi'(x) = \phi(x)-{\omega^{\mu}}_{\nu}x^{\nu}\partial_{\mu}\phi(x)## and hence show that...
  34. 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...
  35. 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...
  36. 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...
  37. U

    How Does Zero Gravity Affect the Tension in Strings of Charged Bodies?

    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...
  38. Shima97

    Electroreception, Electric field and charges

    Hi guys. This is my question. I just wondering what equation that I'm suppose to use. Homework Statement What is the maximum distance at which a shark can detect the electric signal emitted by the trout’s heart if the predator is at a point on an axis passing through the centre of the heart...
  39. H

    What Causes Charged Particles to Spiral in a Magnetic Field?

    Homework Statement Hi! How does a charged particle spiral around a magnetic field lines? Is it because the overal magnetic field interracts with the individual magnetic field of the particle? For example if a piece of metal is put inside magnetic field, the electrons will interract with the...
  40. MidgetDwarf

    Electric Potential Due to point charges

    Homework Statement Two particles each with a charge of +3.00 μC are located on the x axis, with one particle at x = -0.80 m, and the other particle at x = +0.80 m. a) Determine the electric potential on the y-axis at the point y = 0.60 m.b) What is the change in electric potential energy...
  41. D

    Electric Field between two Charges

    Homework Statement A positive charge of 3 microCouloumbs is at the origin. A negative charge with the same magnitude is 8 m away along the x direction. a) What are the magnitude and direction of the electric field at the points between the two charges, 2, and 4, and 6m from the positive charge...
  42. M

    Metal sphere drawn and then repelled by charged rod

    Homework Statement An uncharged metal sphere hangs from a nylon thread. When a positively charged, nonconducting glass rod is brought close to the metal sphere, the sphere is drawn toward the rod. But if the sphere touches the rod, the sphere suddenly flies away from the rod. Explain why the...
  43. Anthony Santelices

    Finding energy in a 4 object charge system

    Homework Statement An object with charge +2.0×10−5 C is moved from position C to position D in the figure (Figure 1) . q1 = q3 = +10.0×10−5 C and q2 = −20.0×10−5 C. All four charged objects are the system. Here's a picture to the problem Homework Equations $$ F = \frac {kq_1 q_2}{r^2} $$ $$...
  44. I

    Velocity of Three Charges Released from Equilateral Triangle

    Homework Statement Three equal charges with charge q and mass m are placed into an equilateral triangle of side length L. Find the speed of each when they are infinitely far from one another. Homework Equations -ΔU =ΔK (since the electric force is conservative), U= 1/4πε Σq1q2 /r The...
  45. heartshapedbox

    Newton's first law, forces, charges

    Homework Statement Two uniform masses of .260kg are fixed at points A and B. Find the magnitude and direction of the initial acceleration of a uniform sphere with mass 0.01kg released from rest at point P that is acted on the gravitational forces of attraction from spheres A and B. The diagram...
  46. 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...
  47. K

    Why moving charges create magnetic field?

    (Sorry my poor English) A changing electric field creates a magnetic field and vice-versa. I thought one field were created only when the another field were disturbed and it works finely for electromagnetic waves, and it agrees with Maxwell's equations. I was happy with my conclusion then I...
  48. neilson18

    What is the potential energy of this group of charges?

    Homework Statement Three electrons form an equilateral triangle 0.800 nm on each side. A proton is at the center of the triangle. Homework Equations U = k[(q_1*q_2)/r] The Attempt at a Solution I tried to use the following equation: k*[(3e^2)/(0.8*10^-9) - (3e^2)/(0.4*10^-9)] I plugged in...
  49. 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...
Back
Top