What is Electric charge: Definition and 274 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. K

    Calculating electric charge from graph (capacitor)

    Apparently, we need to integrate the functions from 0 to the time when it is fully charged. However, I integrated in terms of t so the soultion (according to a graph programme) should be around 236 Vs but I don’t see how this could help me.
  2. C

    Why Does Positive Charge Exert Elec. Field Beyond Neg. Charge?

    I wonder how it is possible that a positive charge can exert el. field beyond negative charge? Shouldn't they "connect" and therefore positive charge should stop to have el. field beyond neg. charge? I mean, I am obviously wrong about that, but can someone please explain why/how el. field from...
  3. rwh2100

    B Gravitational acceleration and sub-atomic electric charge

    Wak a ball with a bat and the ball accelerates. Now under gravity, hold the ball out horizontally, let go and the ball accelerates ... without a wak. Given that gravity arises from curved space-time, I suggest further that the acceleration of the ball arises when sub-atomic particles (in the...
  4. A

    I Calculating Total Electric Charge with a Capacitor and Battery

    With a capacitor with a dielectric with the battery on, ##E_{total} = E_0 + E_i## ##\frac{Q_t}{dC_t} = \frac{Q_0}{dC_0} + \frac{Q_i}{dC_i}## thus, ##\frac{Q_t}{C_t} = \frac{Q_0}{C_0} + \frac{Q_i}{C_i}## since in a battery ##V_t = V_0, V_i = 0##, so either ##Q_i = 0## or ##C_i = infinite## but...
  5. V

    Understanding Fundamentals of Electronics: Solving an Electric Charge Problem

    It's not a homework. I came up with this problem myself. Trying to understand fundamentals of electronics. Do you know how to solve it? Is voltage somehow related to electron energy levels? What knowledge should I gain to be able to solve problems like that? Thank you! If we ground the cathode...
  6. A

    Finding the value of the electric charge

    Hello! I am susposed to find the force of q3.The problem is given as in the picture ; Now we are given a hint,and it says the following: "First calculate the forces of the individual charges on q3. The superposition principle says that you can then simply add these forces vectorially to get...
  7. jackiepollock

    B Problems regarding electrostatic forces in everyday levitation

    Hello! I'm reading this part of the A-level physics book and finding a few places that I couldn't wrap my head around. They are underlined. 1) When saying oxygen, is it saying that oxygen is the most abundant element in the shoe atoms? 2)I am not too sure why the force per atom is shared...
  8. jackiepollock

    I Why are field lines parallel in a uniform field?

    For a uniform field like this, I imagine the two plates that creates it are made of multiple atoms with charges, which are points sources that create radial fields. We know that radial fields don't have parallel fields lines, so how are parallel fields lines form when the field is made of...
  9. P

    I Moving charges in electrostatics

    According to a popular book on electrodynamics a special case of electrostatics is- ''source charges are stationary (though the test charge may be moving)''. My question is- now that the test charge is moving, how is it a special case of electrostatics anymore? Also many times we deal with...
  10. H

    B Distribution of energy in the electric field surrounding an electron

    I am thinking about how an electric field has energy associated with it. If a single electron exists alone in a remote vaccuum, I believe it has it's own electric field surrounding it, and that this field has an energy content associated with it. My question is; does this electric field store...
  11. J

    A Electric charge amplitude mode superconductivity

    Hello, I have a question about the Higgs mode in superconductivity. In this doc, it is said, page 12, that the Higgs mode has no electric charge. But it couples nonlinearly with the photon (in the Ginzburg-Landau theory there is a term A²h with A the vector potential and h the Higgs mode). So...
  12. S

    Electric Charge is basic property of matter or subatomic particles ?

    In some textbooks it is given that - Electric charge is the characteristic property of matter that causes it to experience a force when placed in an electromagnetic field. and In other textbooks it is given that - Electric Charge is the property of subatomic particles that causes it to...
  13. J

    I Equivalence principle: an electric charge and a coil

    The near-range magnetic field ##\vec{B}## of a point charge ##q## at distance ##\vec{r}##, moving at a non-relativistic velocity ##\vec{v}##, is given by $$\vec{B}=\frac{q}{4\pi\epsilon_0c^2}\frac{\vec{v}\times\hat{r}}{r^2}.$$ Faraday's law of induction for the induced EMF ##V_c## in a coil...
  14. F

    Reducing the charge Q on an isolated charged conducting sphere to Q/8

    It seems to me that one can obtain the required result by using just one neutral sphere and one ground wire. Let A be the charged sphere and B be the neutral one. Initially ##Q_A=Q## and ##Q_B=0##. put A and B in contact. As a result ##Q_A=Q/2## and ##Q_B=Q/2##. ground B, so that ##Q_B=0##...
  15. C

    Electrical potential of a thin wire in an E field

    Assume that an infinite metallic plate A lies in the xy-plane, and another infinite metallic plate B is parallel to A and at height z = h. The potential of plate A is 0, and the potential of plate B is constant and equal to V. So, there is a uniform electrostatic field E between plates A and B...
  16. C

    Small doubt regarding electric charge

    Good morning I'm no expert in classical physics, so I have one doubt. If I have a body with mass M, and I charge it electrically with x C (Coulombs), will its mass remain the same, or will it change (in which amount)? Can you help me in the case of a ball, let's say, with 1.5 Kg charged with...
  17. Z

    B Why are there only two types of electric charge?

    Why are there only two types of electric charge? I'm asking as a total layman in science. I've started to wonder about this the more I watch popular science videos about the Standard Model of particles physics and about matter and antimatter. In particular, the various types of subatomic...
  18. T

    Capacitance and induced charge of a spherical Capacitor + dielectric

    I) For the first part I used: ##V = - \int E ds = \int_a^c \frac{1}{4\pi\epsilon_0} Q /r^2 dr+ \int_c^{c+d} \frac{1}{k} \frac{1}{4\pi\epsilon_0} Q /r^2 dr + \int_{c+d}^b \frac{1}{4\pi\epsilon_0} Q /r^2 dr ## And by using ##C = Q/V## We get an answer which is somehow large for writing here...
  19. Mutatis

    Find the electric field at an arbitrary point

    Homework Statement A distribution of charge with spherical symmetry has volumetric density given by: $$ \rho(r) = \rho_0 e^{ \frac {-r} {a} }, \left( 0 \leq r < \infty \right); $$ where ##\rho_0## and ##a## is constant. a) Find the total charge b) Find ##\vec E## in an arbitrary point...
  20. C

    Floating potential of a conductor in an electrical field

    I'm interested in the following general question: Assume x,y,z is an axes system, and that the y-z plane is occupied by a conductive plate at a known potential V with respect to the earth. Now, a conductive material M of neutral global electrical charge is placed at some distance of the plate...
  21. C

    Exploring Electrostatics with Gauss Theorem

    Having come experimentally to an interesting electrostatic effect, I have returned, aged 47, to my old books in physics. It turns out that my books delight in using Gauss theorem etc. in rather ideal geometrical surface charge distribution, but never gave me the tools to answer to this simple...
  22. S

    How spacecrafts discharge static electric charge

    I was wondering how spacecraft s discharge when encountering van allen belts (for example the juno spacecraft around jupiter) since obviously there is no earthing and is it possible to remove excess charge to power something on the craft?
  23. L

    Derivation of the Potential Energy of an Electric Charge System

    Hi, I learned about how PE = U=kq1q2/r is the electrical potential energy for the system. It is found by taking the integral of electrical force and dr from infinity to the point of location we are interested in. So that is the intregral(F*dr) from r=inf to r=ro. My question is that do I...
  24. nashikin58

    How to avoid a clash of magnetic charge and electric charge

    Hi, now I'm working on a project which involves a dc motor and high voltage. I'm developing a machine consists of a motor to rotate a platform disc and high voltage will be applied during the rotation. The problem is when I supply a positive high voltage at motor shaft during rotation, the motor...
  25. S

    What is the electric charge on the charged polystyrene ball?

    Homework Statement A charged polystyrene ball of mass 0.14g is suspended by a nylon thread from a fine glass spring. In the absence of any electric field the spring extends by 30mm. The polystyrene ball is then placed in an electric field that acts vertically upwards, of strength 200kV m^-1...
  26. Islam Hassan

    I Electron/Proton Electric Charge Equality Expected?

    Do the SM and Lambda-CDM lepton-era models predict that the electron’s isolated electric charge be equal in magnitude (to 12 significant figures) to that of the proton which is a composite particle? What makes that this identity in electric charge magnitude is so exquisitely ‘fine-tuned’? What...
  27. J

    What is the minimum charge needed for a ball to jump in an electric field?

    I don't really know how to fit what i want to this template, but i'll try. The thing is that i wonder if anyone can explain to me step-by-step what happened in this solution, because i don't really understand it. Homework Statement There are two balls. Upper one(mass m, charge Q) hung on a...
  28. J

    Electric Field Lines for Two Objects on a Frictionless Table

    Homework Statement In the diagram, two small objects, each with a charge of -4.0nC, are held together by a 0.020 m length of insulating string. The objects are initially at rest on a horizontal, non conducting frictionless table & the effects of gravity on each other are negligible. (b)...
  29. Prof Sabi

    Does electric charge bend anything?

    If mass is considered to bend space time fabric.. does electric charge bends anything?
  30. B

    Electric field inside/outside (uniformly charged sphere)

    A sphere of radius a carries a total charge q which is uniformly distributed over the volume of the sphere. I'm trying to find the electric field distribution both inside and outside the sphere using Gauss Law. We know that on the closed gaussian surface with spherically symmetric charge...
  31. M

    Elementary Charge: Explaining the Integer Multiple of e

    My textbook states: "The magnitude of charge of the electron or proton is a natural unit of charge." and then has an explanation that follows. It states, "...The charge on any macroscopic body is always either zero or an integer multiple (negative or positive) of the electron charge." Here is...
  32. Manolisjam

    Non-conductve sphere with cavity -- find Electric field

    I have a non conducting sphere with a charge ρ=A/r per uni vollume A is constant. suppose there is a cavity in the centre and within a particle of charge q. i want to find the E inside the sphere in respect with r. Homework EquationsThe Attempt at a Solution for radius equal of the cavity i get...
  33. H

    If r=0 then will the electric charge of two points=infinity?

    I found that the electric field at r=0 equals infinity. What if two negative charges were put infinitely close together so the electric field was infinite, then would the charge of those two points be -infinity as well?
  34. M

    Dimension of the electric charge in CGS and in SI?

    The Bohr magneton is (see e.g. Wikipedia) in SI units: $$\mu_B=\frac{e\hbar}{2m_e}$$ and in CGS units: $$\mu_B=\frac{e\hbar}{2m_ec}$$ So the dimension of the electric charge in SI, ##[q_{SI}]##, is related to the dimension of the electric charge in CGS, ##[q_{CGS}]##, by...
  35. Physics Dad

    Find the total electric charge in a spherical shell

    Homework Statement Find the total electric charge in a spherical shell between radii a and 3a when the charge density is: ρ(r)=D(4a-r) Where D is a constant and r is the modulus of the position vector r measured from the centre of the sphere Homework Equations Q=ρV Volume of a sphere =...
  36. Const@ntine

    Chemistry Measuring the Mass & Electric Charge of Molecules

    Homework Statement Hi! So I stumbled upon this simple "plug n' play" exercise in my Physics textbook. Basically it gives you certain molecules/atoms, and tells you to measure the Electric Charge, and its Mass. Pretty simple, but I hit upon some hickups. Anyway, let's get to it: Find the...
  37. Z

    Coulomb's force - magnitude of the electric force

    Homework Statement Show that the magnitude of the electric force on each ball is given by Fe = mgtanθ/ (cosα+ sinαtanθ) where θ = arcsin(x2/L) α = arcsin((y2-y1)/r) r = √((x2-x1)^2+(y2-y1)^2) This is a question from my coulomb's law lab, where 2 styrofoam balls where charged, one was hung on a...
  38. Tania Velarca

    Field lines of a electric charge immersed in two dielectrics

    Homework Statement Hi guys, I hope you can help me with this problem, because I do not have any idea and I could not find anything that could help me, thank you in advance! Draw the electric field lines due to a punctual charge Q immersed in a dielectric medium with constant K1. Q is separated...
  39. Go Nucelar

    B Adding a huge electric charge to a black hole?

    I wonder, what would happen if you started dropping lots of electrons into an existing black hole which otherwise doesn't accrete any new matter? The charge of the black hole would build up much faster than the mass. Wouldn't its charge become so high at one point that further electrons would...
  40. T

    Did i calculate the V/A/R of a plasma arc properly?

    Hello there! So i am currently sitting in my EME class and have nothing to do, so i decided to try spit-balling the V/A/R of the plasma arc my Tesla Lighter produces. note that i did not physically take it apart, and my goal was just to get a rough estimate for the arc itself or at least get a...
  41. H

    A Exploring the Relativistic Origin of Charge-to-Mass Ratio in Electrons

    Hello, Does anyone have informations about a relativistic origin of the charge-to-mass ratio ?
  42. S

    A Electric charge as ##Q = T_{3} + Y##

    My question is about the formula ##Q = T_{3} + Y##. Let us say that there is some complex scalar field that transforms as a triplet of ##SU_{L}(2)##; i.e. ##\psi = \begin{pmatrix} \psi_{1}\\ \psi_{2} \\ \psi_{3} \end{pmatrix}## and ##\delta_{2}\psi = i\omega_{2}^{a}t_{a}\psi## with ##t_{1}...
  43. F

    An electric charge feels its own self electric field

    Hello, In classical electromagnetism, we learn that an electric charge generates and electric field which other charges can feel through a force. But the source charge does not feel its own generated electric field. In reality, a charge feels its own field. Why are we able to ignore this...
  44. RoboNerd

    Question about work on an electric charge

    Homework Statement If the electric field does positive work on a negative charge as the charge undergoes a displacement from point A to point B within an electric field, then the electric potential energy is a) negative b) positive c) increases d) decreases e) electric fields can not do work...
  45. killershek


    In case of wire(having uniform linear charge density), without assuming the wire infinite long, why we can't take electric field perpendicular to the curved part of the cylindrical Gaussian surface?
  46. F

    Question about electrical potential energy

    Homework Statement Two charged plate hold a charge of 3 coulombs with the upper plate being positively charged and the lower plate being negatively charged. They have a pd of 6 volts. There is a spacing of 20 cm between them. A positive charge q with a charge 0.4 coulomb is located at midpoint...
  47. Cimino54

    Square Electric Charge Problem

    Homework Statement Four charges, q1 = +145 µC, q2 = +55 µC, q3 = −150 µC, and q4 = +27 µC, are fixed at the corners of a 4 m by 5 m rectangle, as illustrated in the figure below. What are the magnitude (in N) and the direction (in degrees counterclockwise from the +x-axis) of the net force...
  48. C

    Calculating Tension Forces on Charged Balls Suspended by Strings

    Homework Statement Two identical balls (B and C) with a mass of .5 g are suspended from two strings as shown above. The balls carry equal charges +10nC each and are separated by a distance of 4 cm. A. Draw the free-body diagram and show all forces applied to ball C. B. Find the tension force in...
  49. C

    Electric Charge and Force free body diagrams

    Homework Statement A positive charge Q1 = 7.4 μC is located at a point X1 = -2 m, a negative charge Q2 = -9.7 μC is located at a point X2 = 3 m and a positive charge Q3 = 2.1 μC is located at a point X3 = 9 m. Draw free body diagrams for the electric force acting on Q1, Q2 and Q3. Find the...
  50. UseAsDirected

    B Why are two cellophane tapes attracted when ripped apart?

    Hello, I put two strips of cellophane tape adjacent to each other adhered onto a table. When I pull them both apart, they repel each other, both insulators ripped electrons from the wood. When I stack two strips of tape on top of each other on a table, rip the combined bundle off the table...