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. psy

    Electrostatic Force and Field between two charges

    Two positive point charges with a charge of 10nC each are 10cm apart. What is the electric field strength at point A? How is it directed? Which force acts on a charge of 100nC at point A? F = k * q1 * q2 / r^2 E = F/q r^2 = (l1/2)^2 + (l2)^2 => r = 0,707m Electric field strength : E1 = E2 =...
  2. A

    Finding the New Acceleration Given Point Charges

    Homework Statement A point charge q1=15.00μC is held fixed in space. From a horizontal distance of 8.00 cm , a small sphere with mass 4.00×10−3kg and charge q2=+2.00μC is fired toward the fixed charge with an initial speed of 40.0 m/s . Gravity can be neglected. What is the acceleration of the...
  3. N

    Velocity of a charged particle as it approaches infinity

    Homework Statement Homework Equations F = k(q1q1/r^2) K = (mv^2)/2 The Attempt at a Solution I got number 18 easy enough, number 19 seems simple but I'm not getting the right answer. I'm calculating Force exerted by each charge on the new charge using F = k(q1q1/r^2) for the three charges...
  4. J

    How can I plot the electric field vs position for two charges?

    Homework Statement :- electric field vs position how to plot it[/B]Homework Equations :- force per unit charge[/B]The Attempt at a Solution :- i know option 1 and 2 can never be an answer to this question but still i am confused between 3 and 4 option and help me solve with proper equation[/B]
  5. J

    What is the initial charge of the second object in Coulombs?

    Homework Statement Suppose an object has a charge of 1 C and gains #9.38 ✕ 10^18# electrons. When another object is brought in contact with the first object (after it gains the electrons), the resulting charge on the the second object is 0.9 C. What was the initial charge (in Coulombs)...
  6. J

    How do the electroscope leaves behave after grounding?

    Homework Statement A positively charged rod is brought near the knob of an uncharged electroscope and the leaves of the electroscope diverge. As the positively charged rod is held near the knob, the electroscope is grounded with a wire. Then the grounding wire and the positively charged rod...
  7. C

    What does electrical PE turn into when charges attract?

    for instance. Let's say we have a positive charge and a negative charge. and i do 30 joules of work to pull the negative charge away from the positive charge. now it has 30 joules of electrical PE. I release it. All the turns into KE as it flies back towards the positive charge. once it...
  8. A

    Point where the electric field is zero

    Homework Statement Charges q1= +3 nC and q2=+8 nC have a separation distance of d= 12 cm. Find the point where the electric field is zero. Homework Equations E=kq/r2 The Attempt at a Solution I approached this problem as follows: 1) I assume the point where it happens is between charges, on...
  9. radiant_june

    Electric field strength at a point between charges

    Find the electric field strength at point B between two charges shown below: Given/Known Values q1 = 4.0×10-6 C r1 = 40 cm = 0.4 m (Distance from q1 to point B) q2 = -1.0×10-6 C r2 = 30 cm = 0.3 m (Distance from q2 to point B) k = 9.0×109 Nm2/C2 Equations Electric Force: FE = (k⋅q1⋅q2)/r2...
  10. ?

    EM fields of two opposite moving point charges

    I wrote and solved this problem but am having serious doubts about the answer I obtained. Homework Statement Two point charges \pm q move along the z-axis with velocity \pm v. If they are at the origin when t=0, what is the electric field magnitude a distance r from the z-axis? Homework...
  11. F

    Gauss’ law and Enclosed Charges

    What exactly does the electric field as solved for by Gauss’s law tell us? If you use a Gaussian surface that encloses no charge you find that the electric field is equal to 0. But if there is a charge outside of that Gaussian surface, it is not true that the electric field is 0 on the Gaussian...
  12. K

    Charges of ions in a mass spectrometer

    Homework Statement In a mass spectrometer, a few 126C ions are deflected with a radius of 12.9 cm. The ions have a speed of 5.67*10^4 m/s when they enter the field. The magnetic field has a strength of 3.2*10^-2 T. The charge of these ions must be ... SOLUTION: We use the formula: i F=qvB =...
  13. K

    What charges generate EM waves in free space?

    as we know light travel in vacuum because of oscillation of electric and magnetic field and both are perpendicular to each other. But i don understand how these electric and magnetic fields get generated in vacuum. as electric filed can vary by oscillating charge and that generate varying...
  14. E

    Charges pushed to the ends of a pole -- Faraday's law

    Homework Statement We put a pole with a length of 0.2m in a magnetic field equals to 0.4T and move it with a velocity of 4m/s. What is the value of the charges that accumulate in the ends of the pole? Homework Equations E=Bv ε=El The Attempt at a Solution I know that E=1.6V/M and ε=0.32V (Book...
  15. Hydrous Caperilla

    Find Charges on Capacitor w/ Floating Plates

    Homework Statement Ignore those darkened black lines as they are just consequences of my editing and there's a SWITCH" between A and C2 which is opened initially So here's the question I was working with. The switch is closed at t=O,find the charges on the capacitor.The batteries are both 2OV...
  16. A

    Three charges constrained to a ring

    Homework Statement Three non-equal positive point charges, q1, q2, and q3, are constrained to a ring of radius r. Find their relative positions in equilibrium using force balances. Homework Equations I know that this problem could be approached in two ways: using force balances or minimizing...
  17. T

    What force holds together like charges in a capacitor, or a battery

    I was wondering what force hold together like charges in capacitor, battery... we have a capacitor having two oppositely -charged plates so my question is what holds the electrons with electrons in one plate and what holds protons with protons in other plate since like charges repel each other...
  18. G

    Gauss's Law and Parallel Line Charges

    Homework Statement Find an equation for the net electric field at a point, above and between, two infinite line charges, one with line charge density λ and the second with line charge density -λ. The point is a distance R from both line charges, a distance y above the midpoint between charges...
  19. Ignitia

    Position of two point charges

    Homework Statement "Can you arrange the two point charges q1 =−2.0×10−6 C and q2 =4.0×10−6 C along the x-axis so that E =0 at the origin?"Homework Equations E = K (|q|/r2) K = Coloumb Constant The Attempt at a Solution Since one particle is negatively charged and the other is positively...
  20. lawsonfurther

    Why can't excess charges leave the surface of a conductor?

    My question is basically similar to a thread that was posted 12 years ago: https://www.physicsforums.com/threads/electrons-flying-off-a-conductor.119269/ I was glad to see that there was already a thread which asked my question in the forum. But when I read through all of the discussion, I don't...
  21. A

    Confusion regarding Electric Potential Energy and Work

    Hi everyone. I've been doing a lot of reading regarding electric potential and electric potential energy. Unfortunately, I have a lot of confusion regarding this topic, as I keep receiving different information. My main confusion is regarding the signs, positive or negative, of work and it's...
  22. S

    Find the electric field at the point 20cm above the centre

    Homework Statement Hi guys, I was hoping I could get some help on this question! The question: "Find the electric field at the point 20 cm above the center of the square made of 4 charged rods of L = 20cm and Q=1mc each. Homework Equations I believe E = (KQ)/r^2 is the only equation needed...
  23. Hiero

    Does the superposition of electric fields not hold for moving charges?

    If a single point charge is moving, then the component of the electric field normal to the motion is larger (by the gamma factor) than if the charge were stationary. Now consider an infinite line of charges (with a small separation, the same between each charge). If the whole line is moving...
  24. P

    Dielectric problem -- two line charges inside a dielectric cylinder

    Homework Statement Consider a cylindrical hole of radius a and infinite length cut into a dielectric medium with relative electric permittivity ε (the interior can be treated as a vacuum). Inside the hole there are two line charges of infinite length with line charge densities λ and −λ...
  25. C

    Can an axisymmetric electric field be created without charges?

    That is, a field that accelerates charges in opposite directions on each side of an axis. I was thinking about interference of similarly polarized waves traveling in opposite directions (so that electric field peaks and valleys overlap but magnetic field adds constructively) - would there be an...
  26. T

    How charges can flow in circuit wires at the same potential

    I have this simple circuit I know that if a consider the wire from the + of the battery until the + extreme of the resistor, in this portion the wire has the same potential. The same thing regarding the portion of the wire beetween the - of the battery until the - of the resistor. If this...
  27. S

    Individual Charges and voltage

    Homework Statement the capacitance of each capacitors and the cell voltage Homework EquationsThe Attempt at a Solution I got the total capacitance = 8028/5333 uF total voltage = 36v total charge=289008/5333 uC
  28. allison west

    Semi-infinite slab of charges -- find E and charge density

    Homework Statement A semi-infinite (infinite in y and z, bounded in x) slab of charges carries a charge per unit volume ##\rho##. Electric potential due to this slab is a function of horizontal distance, x from the center of the slab. It is linear for ## x \lt -1m## & ## x \gt 1m##, and is...
  29. M

    What Is the Escape Speed of an Electron from a Charged Glass Sphere?

    Homework Statement What is the escape speed of an electron launched from the surface of a 1.0-cm-diameter glass sphere that has been charged to 10nC? Homework Equations Given: d= 1.0cm r= 0.05cm= 0.0005m q1 = 10nC = 10 x 10-9 (sphere) q2 = -1.6 x 10-19 (electron) Equation: U = (kq1q2)/r KE=...
  30. M

    Determining speed of electron in a parallel plate capacitor

    Homework Statement A proton is released from rest at the positive plate of a parallel plate capacitor. It crosses the capacitor and reaches the negative plate with a speed of 50,000 m/s. What will be the final speed of an electron released from rest at the negative plate? Homework Equations...
  31. A

    Accelerated Electron and its Potential Energy

    Homework Statement An electron acquires 3.16*10^-16 J of kinetic energy when it is accelerated by an electric field from plate A to plate B. What is the potential difference between the plates, and which plate is at the higher potential. Homework Equations w =Δv * q The Attempt at a Solution...
  32. A

    Finding the final speed of a Positive and Negative Charge

    Homework Statement This is an example problem I found on khan academy and it didn't have an official problem statement... So I am going to have to make up my own problem statement from what was given. I can link the video if any of you want to see it. A positive charge 4uC and a negative...
  33. I

    Electromagnetic waves/radiation properties?

    As I understand it, light is an electromagnetic wave consisting of an oscillating electric and magnetic fields perpendicular to each other. Are there experiments that will demonstrate (a) there is an electric field present? Stark effect? (b) a magnetic field, (c) that they are perpendicular to...
  34. M

    How to calculate the force of a charge through its kinetic Energy?

    Good Afternoon Is it correct to calculate the force of a point charge by relating the force to the kinetic energy and this with its derivative? I have the graphic V/r (Velocity Vs Space), want to calculate force, relate work with force in this way: W=ΔEk, in my case the kinetic energy initial is...
  35. Y

    Why do charges outside surface create no net flux?

    Why do charges outside the surface contribute 0 net flux? The book I'm reading says it's because the flux entering the surface cancels out with the flux exiting the surface. But that means E dot Area must be exactly the same magnitude when entering and exiting to cancel out. But we know E-field...
  36. R

    Conservation of energy -- Two charges separated by a spring

    1. Two identical charged particles which are point masses are fastened to the two ends of a spring of spring constant 100 N/m and the natural length 10cm.The system rests on a smooth horizontal table.The charge of each particle is 2*10^(-8)C.the extension of spring if the extension is small as...
  37. W

    I Positive Charge Magnetic Fields: Real World Examples

    As a SP phenomena I thought this may be the best sub to post this. We understand how current creates a magnetic field, and almost all forms of current are really electron flow. My question is - are there any known (real world) examples of positive particle flow, creating a magnetic field...
  38. Y

    E-field from uniformly distributed charges on sphere?

    So if I have a sphere of uniform charge distribution, the electric field at one point away from the circle would be affected by ALL individual charges distributed across the circle, right? From the picture I drew, there would only be a net effect of E-field in the X direction because there...
  39. mark!

    How many different charges are there in nature and why?

    Protons are +1 charged, electrons -1, so that's makes two charges, but how does antimatter charge relate to normal matter charge?
  40. P

    Emitting one or two opposite charges along the x-axis

    Let's consider that I have an emitter that can emit both negative and positive electric charges. Here let's consider only scenarios with two particles (one negative and one positive) that start initially at the tip of some electrode, where one or both the charges will separate from at the same...
  41. S

    Coulomb's Law, Three Charges, X Y Components, Angle

    Homework Statement This is finding net force on Q3. I was taught by my Physics teacher to always get angle from the Positive side of x-axis (+X-Axis). For example in the above situation, if the angle is -30deg from the +x-axis (assuming the Q3 is the origin), Why is F31 x-component = 140...
  42. S

    Correction to the field energy due to the existence of discrete charges

    In the classical electromagnetic field theory, the field density of energy is given by: $$u = (\epsilon/2)E^2 + (\mu/2)H^2$$ One of the differences between the classical electromagnetic theory and the real world is that in classical EM all charge and current density, (ρ(r), J(r)), is...
  43. Epoch

    Electricity: electric field in a point Between Two Charges

    Homework Statement I've seen many books writing the cosine rule like this: a^2 = b^2 + c^2 - 2bc cos A My electricity textbook for an electric field in a point between two charges says this: E resultant = root[E1^2 + E2^2 + 2*E1*E2*cos(angle between E1 and E2)] In the first equation it is -2...
  44. M

    Finding electric potential given two point charges

    Homework Statement Find the potential at points P1, P2, P3, and P4 in the diagram due to the two given charges. Homework Equations VP =k∑qi/ri p = q ⋅ d The Attempt at a Solution I'm not sure how to approach the problem. I thought about using that given equation four times and adding it all...
  45. B

    Force on a 3rd point charge due to 2 other point charges

    Homework Statement Two positive charges q1 = q2 = 2.0 μC are located at x = 0, y = 0.30 m and x = 0, y = -0.30 m, respectively. Third point charge Q = 4.0 μC is located at x = 0.40 m, y = 0. What is the net force ((a)magnitude and (b)direction) on charge q1 exerted by the other two charges...
  46. Eclair_de_XII

    Force on a test charge due to two point charges?

    Homework Statement "Let there be two point charges ##q_1=3.5μC## and ##q_2=-3.5μC## located at ##(0,0.3 m)## and ##(0,-0.3 m)## respectively. What force do these two charges exert on a test charge ##Q=4.5μC## at ##(0.4 m,0)##?" *title should read "due to two point charges"* <Moderator's note...
  47. M

    Forces of 3 charges in an equilateral triangle?

    1. The problem statement: in the first photo all variables and given/known data, Homework EquationsThe Attempt at a Solution : i wrote it all down in the second photo [/B]
  48. C

    Field pattern -- Which can be produced by 2 point charges?

    Homework Statement Homework EquationsThe Attempt at a Solution why not B?
  49. J

    How come accelerating charges produce EMR, but others don't?

    I am a high school teacher preparing to teach grade 12 physics for the first time in the fall. I can't quite understand this and it is really bothering me... In the textbook my school uses, it says that accelerating charges produce electromagnetic radiation, while charges moving at a constant...
  50. J

    A sphere radiating charges isotropically

    An interesting problem posed to me by a friend: A small sphere, initially neutral, of radius ##a## emits ##n## charges ##q## of mass ##m## per unit time isotropically from its surface at a radial velocity of constant norm ##v##. Determine the spatial distribution of charges and currents at...
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