What is Gauss law: Definition and 181 Discussions

In physics and electromagnetism , Gauss's law, also known as Gauss's flux theorem, (or sometimes simply called Gauss's theorem) is a law relating to the distribution of electric charge to the resulting electric field. In its integral form, it states that the flux of the electric field out of an arbitrary closed surface is proportional to the electric charge enclosed by the surface, irrespective of how that charge is distributed. Even though the law alone is insufficient to determine the electric field across a surface enclosing any charge distribution, this may be possible in cases where symmetry mandates uniformity of the field. Where no such symmetry exists, Gauss's law can be used in its differential form, which states that the divergence of the electric field is proportional to the local density of charge.
The law was first formulated by Joseph-Louis Lagrange in 1773, followed by Carl Friedrich Gauss in 1813, both in the context of the attraction of ellipsoids. It is one of Maxwell's four equations, which forms the basis of classical electrodynamics. Gauss's law can be used to derive Coulomb's law, and vice versa.

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  1. Const@ntine

    Gauss' Law: Charged Rod & Sphere (Electric Flux)

    Homework Statement A charged, straight line/rod of infinite length has a Discrete uniform distribution of charge, has a linear density of λ and is at a distance d from a sphere with a radius of R. Find the entirety of the Electrical Flux that is caused by this charged rod, which passes...
  2. Pushoam

    Elec. flux through the top side of a cube with q at a corner

    Homework Statement Find the electrix flux through the top side of a cube. The cube's corner is on the origin, and is 'a' units on length. The charge 'q' is located at the origin, with the corner of the cube. Homework Equations Gauss's law and symmetry The Attempt at a Solution I take 8 cubes...
  3. E

    Gauss' Law for electromagnetic radiation?

    For the proof I've read that verifies transverse electromagnetic waves are consistent with Gauss' Law, there seems to be the suggestion that the magnetic and electric field at a given small length c(dt), along which the waves travel, propagate infinitely backwards and forwards in their...
  4. D

    Electric potential related to electric field question

    Homework Statement (i) Consider a non-conducting sphere of radius R with non-homogeneous charge density ρ = ρ(r) = r, where r is the radial co-ordinate. (a) Find the electric field inside and outside of the sphere(b) Find and plot the electric potential inside and outside of the sphere...
  5. F

    Electric potential of charged concentric spheres

    Homework Statement Two conducting concentric spheres of negligible thickness. The radii of the spheres are R_1 and R_2, respectively, with R_2>R_1. A charge q_2 is placed on the external sphere. A charge q_1 is placed on the internal sphere. Assume that the electric potential is zero...
  6. A

    Capacitance capacitor parallel plate with dielectric (Gauss)

    Homework Statement I have an elementary doubt with the calculation of the capacitance of a capacitor of parallel plates that has a dielectric in the middle. https://ibb.co/b0W4BQ Homework Equations ∫D⋅ds=Q D=E+γP C=Q/V The Attempt at a Solution Suppose the top plate has a positive charge...
  7. G

    Gauss' Law - Electric Field for a Charged Metal Plate

    Homework Statement An infinite metal plate has a surface density of charge σL=-6μC/m² , Left side and a surface density Of load σR=+4μC/m² , in the right side. A Gaussian surface In the form of a circular cylinder, with area A 12 cm², is Located with the left side inside the plaque and a thin...
  8. Arman777

    Cylinder rod charge density (Gauss Law)

    Homework Statement Theres a cylinder rod inner radius a outer raidus b.we want to find electric field between a and b,like point r (or radius r) a<r<b. Homework Equations Gauss Law The Attempt at a Solution [/B]I am trying to find Q enclosed but something make me confused.I am...
  9. Arman777

    Uniform Slab-Finding Electric Field Using Gauss Law

    Homework Statement Uniform Slab: Consider an infinite slab of charge with thickness 2a. We choose the origin inside the slab at an equal distance from both faces (so that the faces of the slab are at z = +a and z = −a). The charge density ρ inside the slab is uniform (i.e., ρ =const). Consider a...
  10. R

    Capacitor with uniform space charge between them

    Homework Statement 2 large plates are separated by a distance d and a space charge of uniform charge density p is placed between them and a potential difference V is applied across the plates. Find the electric field stength at a distance x fromt the positive plate The answer is -V/d...
  11. A

    Electric field of a washer (hollow disk)

    Homework Statement A washer made of nonconducting material lies in the x − y plane, with the center at the coordinate origin. The washer has an inner radius a and an outer radius b (so it looks like a disk of radius b with a concentric circular cut-out of radius a). The surface of the washer is...
  12. Toby_phys

    Understanding Cylindrical Capacitors: Charged vs. Disconnected

    Homework Statement Normally this style of question wouldn't be too bad, however the 2 different parts confused me. Surely once set to a potential V, it would stay at that potential - it doesn't need to stay connected How are the 2 parts any different from each other?
  13. RoboNerd

    Resistor made from two materials

    Hi everyone, I am having problems figuring out how to solve a particular problem. Because I was not able to access PhysicsForums recently, I typed everything about my issues into a pdf file that I have attached below. I am grateful for your help in advance, and make it a great day...
  14. haseeb

    Solving potential of electron inside the nucleus

    Homework Statement I want to derive the following equation. It is the potential energy of an electron inside a nucleus assumed to be a uniformly charged sphere of R.Homework Equations V'(r) =( -Ze2/4∏ε0R)(3/2 - (1/2)(r/R)^2) The Attempt at a Solution I get E = Ze2r/(4∏ε0R3) But I am having...
  15. G

    Faraday cage from Gauss' law alone?

    Hi. Is it possible to derive the properties of a Faraday cage from Gauss' law alone? I found some "derivations" which I find rather unconvincing since they somehow conclude from a vanishing flux that the E field must vanish as well. Some slightly more elaborate derivations use a combination of...
  16. LAByrinthAC

    Can Gauss's Law Derive the Electric Field Around a Uniformly Charged Ring?

    Hey guys can we derive the formula of Electric Field Intensity around a uniformly charged ring if yes please share the derivation thanks
  17. math4everyone

    Proving Gauss Law using a "bad" Gaussian surface

    Homework Statement What I basically want to do is to prove Gauss Law with a cylinder perpendicular to an infinite charged wire (I know I can do this simple, but I want to do it this way) This is what I have done so far: Homework Equations $$\Phi=\int \frac{dq}{4\pi \varepsilon_0 r^2} \hat{r}...
  18. Blockade

    What are the different kinds of charge density?

    At this point I was given rho, sigma and landa to hold value of these three different kinds of density ρ = Charge/Volume -------------- Volume Density σ = Charge/Area ----------------- Area Density λ = Charge/Length ---------------- Length Density How do I know which type of density to use over...
  19. Magnetic Boy

    Electric field calculated by gauss law

    Which one is correct?? 1) electric field calculated by gauss law is the field due to charges inside the closed surface. 2) the flux of the electric field through a closed surface due to all charges is equal to the flux due to charges enclosed by the surface
  20. K

    Spherical Shell using Gauss' Law

    Homework Statement An insulator is in the shape of a spherical shell. The insulator is defined by an inner radius a = 4 cm and an outer radius b = 6 cm and carries a total charge of Q = + 9 C (1 C = 10-6 C). You may assume that the charge is distributed uniformly throughout the volume of the...
  21. P

    What is Electrical Field in a Closed surface with no charge

    As per the Gauss Law , Net Flux Electric Field through a closed Surface (Gaussian Surface) is zero if no charge is enclosed. As per the definition of the Electrical Flux = Electrical Field Intensity dot product Area Vector i.e. Closed Integral of E.S If Electrical Flux is zero then as per the...
  22. Ian Baughman

    Electric Fields (Uniformly Charged Plates)

    Homework Statement In the figure two large, thin metal plates are parallel and close to each other. On their inner faces, the plates have excess surface charge densities of opposite signs and magnitude 7.76 × 10-22 C/m2. What is the magnitude of the electric field at points (a) to the left of...
  23. RoboNerd

    Question about problem solving approach to Gauss' Law

    Homework Statement Hi, I am studying gauss's law via this book below.[/B] http://faculty.polytechnic.org/cfletcher/Phys%20With%20Calc_Vol_2_web_pdfs_2010/i-Ch14-PCALC--GAUSS'S%20LAW.pdf On page 8, and 9, the book describes the shell method of finding the volume of the sphere and then using...
  24. F

    Gauss' Law between infinite plates

    Homework Statement The volume between two infinite plates located at x=L and x=-L respectively is filled with a uniform charge density ##\rho##. Calculate the electric field in the regions above, between and below the plates. Calculate the potential difference between the points x=-L and x=L...
  25. 1

    What does divergence of electric field = 0 mean?

    Homework Statement I just want to focus on the divergence outside the cylinder (r >R) Homework Equations The Attempt at a Solution For r > R, I said ∇ * E = p/ε But that's wrong. The answer is ∇ * E = 0 I'm confused because there is definitely an electric field outside the cylinder (r...
  26. C

    I Divergence Theorem and Gauss Law

    Divergence theorem states that $\int \int\vec{E}\cdot\vec{ds}=\int\int\int div(\vec{E})dV$ And Gauss law states that $\int \int\vec{E}\cdot\vec{ds}=\int\int\int \rho(x,y,z)dV$ If $\vec{E}$ to be electric field vector then i could say that $div(\vec{E})=\rho(x,y,z)$ However i can't see any...
  27. L

    Gauss' Law & charge inside sphere

    1. Homework Statement I need to find the total charge inside the small metal sphere, inside the big metal sphere as well as outside the big metal sphere. Homework Equations What confuses me is the electric field vector. Since it's only poiting in one direction it can't originate from a...
  28. M

    MHB Gauss Law and field charge

    I need to prove that the field charge of 2 infinite, oppositely charged plates is 0 using Gauss' law. I know that the sum of E=4PiK(Sum of q) but I don't know how to prove the charge is 0.
  29. P

    This formula is applicable for a point charge distribution.

    1. The problem: A Geiger-Mueller tube is part of a Geiger counter, a device used to count the number of ionizing particles passing through it. It consists of a conducting outer cylinder held at zero electric potential with a thin central wire held at an electric potential of roughly 1000 volts...
  30. annoyingdude666

    Why infinite conducting rod - Gauss's Law , uses lambda?

    hi, i still don't understand why infinite thin-walled cylindrical shell or conducting rod use lambda rather than sigma ? lambda = C/m ,,, sigma = C/m^2 i mean when we look at conducting rod, the charges inside the conductor is zero, so the charges spread on the surface of conducting rod(have...
  31. engnrshyckh

    Surface Charge Density of Coaxial Cylinder with Canceling Electric Fields

    a long straight wire has fixed -ve charge density of 39nC/m. the wire is enclosed by thin wall non conducting coaxial cylinder of radius 1.7m. the shall has positive charge density and its Field is such as that it will cancel the field due to wire. what will be the surface charge density of...
  32. Titan97

    Finding flux from electric field

    Homework Statement If ##\vec{E}=k\frac{x\hat i +y\hat j}{x^2+y^2}##, find flux through a sphere of radius R centered at origin. Homework Equations ##\int E.da=\int(\nabla\cdot E)\cdot da## The Attempt at a Solution I was able to solve this problem without finding divergence of electric field...
  33. D

    Electric field inside and around a hollow sphere

    Hi everyone, I am wondering if anybody could help me out. For my study I got the following question but I got stuck in part C (see image below). I Found at A that due to symmetry all components which are not in Ar direction will get canceled out I found at B that there is only charge density at...
  34. SarahAlbert

    Gauss Law: Concentric Spheres

    Homework Statement Two concentric spheres have radii a and b with b>a. The region between them is filled with charge of constant density. The charge density is zero everywhere else. Find E at all points and express it in terms of the total charge Q. Do your results reduce to the correct values...
  35. X

    Determine charge at origin, based on charge density function

    Homework Statement a) and b) are no problem. I need help to solve c) and d) Homework Equations c) Delta dirac function Gauss' law d) Gauss' law ## \int_V {\rho \, d\tau} = Q_{enclosed} ## The Attempt at a Solution By taking laplace on the potential I get: ## \rho(\mathbf{r}) =...
  36. T

    Exploring the Limitations of Gauss's Law: A Case Study of a Line Charge in Air

    Homework Statement A line charge exists in air along the z-axis between z=0 and z=5 cm. It has a uniform charge density given by: ρl = 4(uC/m) Determine E at (0,10 cm, 0) Homework EquationsThe Attempt at a Solution [/B] I am using gauss law so I draw a cylinder around the wire Qenc = ρl *...
  37. P

    Electric Flux and Gauss's law

    Homework Statement 1) A large cube has its bottom face on the x-z plane and its back face on the x-y plane. The corners on the x-axis are at (3.39 m,0,0) and (12.3 m,0,0). The cube is immersed in an electric field pointing in the positive x-direction, and given by: E = (91.2x^2 - 2.9)i, x is...
  38. SquidgyGuff

    Distance independence of electric field strength

    I was just wondering why the strength of the electric fields of insulating surface charges like sheets and shells aren't dependent on the distance from the charge according to Gauss's Law?
  39. G

    Electrostatics: Find relative permitivitty

    Homework Statement Spherical capacitor with two linear and uniform dielectrics with relative permitivitty Ɛr1 and Ɛr2 is connected to constant voltage U. When second dielectric is removed, intensity of electric field by inner electrode is reduced by 1/3, and electric field by outer electrode...
  40. T

    Two touching neutral conductors in electric field separate?

    Homework Statement Given a situation like this: Where the two blocks are perfectly conducting materials and are touching, will they separate? If they do separate, will they have the net charge values you calculate in the initial setup using Gauss's Law? There are no numbers, it's just...
  41. K

    Dot product vs trigonometry in Gauss' law

    I'm currently writing my EP on various physical equations including Maxwell's equations, and I had to justify using the dot product of the normal unit vector and the electric field in the integral version. However, I can't think of a reason for not using trigonometry as opposed to the...
  42. G

    Electrostatics:Longitudinal charge density of conductors

    Homework Statement Three very long (theoretically infinite long) hollow cylindrical conductors, with radius a,b,c (c>b>a) are in vacuum. Inner and central conductor are charged, and outer conductor is grounded. Potentials of inner and central conductors with reference point relative to outer...
  43. U

    Charge inside and outside conducting shell

    A thin metallic spherical shell contains a charge Q over it. point charge +q is placed in side the shell at point T separated from the centre by a distance a. Another point charge q1 is placed outside the shell at a distance b from the centre find the electric field at the centre due to the...
  44. Alettix

    Potential of a Spherical Shell

    Hi! I have trouble with solving this problem and would be really thankful for some help. :) 1. Homework Statement Inside a thin, spherical metal-shell with a radius of 50 cm, a smaller homogenous metal-sphere with a radius of 20 cm is placed concentrically. The smal sphere is grounded through...
  45. H

    Gauss Law for finite line/plate

    Homework Statement I just noticed that whenever I'm doing a problem involving Gauss Law, it always involves an infinite line/plate. I can't seem to figure out why it must be infinite large/long. Here is an explanation I read, but don't quite understand...
  46. P

    Gauss Law in a plane sheet, and thick sheet (Infinite)

    We have learned the below formula for a plane sheet of charge with thickness. E=σ/ϵ and the one below for with no thickness (negligible) E=σ/2ϵ The problem, I am facing is digesting the derived equations. It is one thing for sure that these formulas must be right. But then the fact that E...
  47. ?

    Calculating Electric Flux and Net Force on Charged Particles | Homework Help

    Homework Statement The total electric flux from a cubical box 34.0 cm on a side is 1.29 x 103 N·m2/C. What charge is enclosed by the box? ----and---- Three charged particles are placed at the corners of an equilateral triangle of side d = 1.00 m (Fig. 16-53). The charges are Q1 = +4.0 µC, Q2...
  48. 1

    Electric Field and Potential Difference in a Coaxial Cable

    Homework Statement : [/B] Co-axial cable, relative permittivity, capacitance, internal energy A long straight co-axial cable of length 1 consists of an inner conductor of radius r1 and a thin outer conductor or radius r2. The dielectric between the conductors has a relative permittivity εr...
  49. M

    Flux Through a Non-Concentric Sphere

    Homework Statement Assume I want to calculate the electric flux through a spherical surface centred at point P with radius R which contains a point charge Q, that is not concentric with the spherical surface. Here, I can no longer assume that ∫∫sEdA = E.A, and I have to calculate the value of...
  50. P

    Electric field at point Gauss law

    Homework Statement We won't to find out the electric field at a point p due to a point charge q placed at o as shown in the figure [/B] Consider a sphere of radius r passing through the point p. Let the electric field at p be E then by Gauss law my problem is how we get the last step? I...
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