Gauss' law Definition and 341 Threads

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. P

    Gauss' Law (Why the opposite sign?)

    Homework Statement 4. In Fig. 23-28, a butterfly net is in a uniform electric field of magnitude {E = 3.0} mN/C. The rim, a circle of radius a = 11 cm, is aligned perpendicular to the field. The net contains no net charge. Find the electric flux through the netting...
  2. B

    Use Gauss' Law to find the magnitude of E in a sphere

    Problem Problem 27.56 A sphere of radius R_0 has total charge Q. The volume charge density (C\m^3) within the sphere is \rho(r) = C/(r^2), where C is a constant to be determined. Part A The charge within a small volume dV is dq = \rhodV. The integral of \rhodV over the entire volume of...
  3. E

    Solve Gauss' Law: Volume Charge Density in Region r > a

    Homework Statement An electric field in the region r > a is given by E,r = 2*A*cos(theda)/r^3 E,theda = A*sin(theda)/r^3 E,phi = 0 A = constant Find the volume charge density in this region. E,r and E,theda and E,phi are the components of E in the r, theda, and phi directions...
  4. F

    Solving Gauss' Law for a VDG Dome: Electric Field at 25cm

    Homework Statement Use Gauss' law to find the charge density on a Van Der Graff dome (r=40cm) if it is charged to 100kV. What is the electric field strength at r=25cm? I understand gauss's law and I know that I need to use it to find the total charge enclosed on the dome. I can then work out...
  5. D

    Gauss' law to calculate electric potential

    I would appreciate hints on how one can calculate the dependence of the electric potential as a function of distance r from an isolated charge Q in 5-dimensions
  6. S

    Solving "If the Photon Had Mass m" Problem with Gauss' Law

    hi I have this question, I need your help: If the photon had mass "m" , show that the Gauss' law would no longer be true. Note that the electric poential for a point charge would then have a form V(r) = e/r exp ( -mc/h * r ) Thank you
  7. S

    .Showing Gauss' Law is False with Photon Mass "m"

    hi I have this question, I need your help: If the photon had mass "m" , show that the Gauss' law would no longer be true. Note that the electric poential for a point charge would then have a form V(r) = e/r exp ( -mc/h * r ) Thank you
  8. S

    Solving Gauss' Law: E Field & Volume Charge Density

    Homework Statement 1.)Two large metal plates of area 1.0m^2 face each other. They are 5 cm apart and have equal but opposite charges on their inner surfaces. If the magnitude E of the electric field between the plates is 55N/C, what is the magnitude of the charge on each plate?Neglect edge...
  9. R

    Electric dipole and Gauss' Law

    We have an electric dipole. Now, let us draw a Gaussian surface around our electric dipole. Now, the total charge enclosed by our Gaussian surface is zero, so according the Gauss' Law the flux through the Gaussian surface is zero, and so is the electric field intensity due the electric dipole...
  10. Y

    Gauss' Law - Planar Symmetry HELP

    Homework Statement A square plate of edge length 9.0 cm and negligible thickness has a total charge of 6.3 x 10-6 C. (a) Estimate the magnitude E of the electric field just off the center of the plate (at, say, a distance of 0.50 mm) by assuming that the charge is spread uniformly over the...
  11. S

    Cylindrical Shells and Gauss' Law

    Homework Statement An infinitely long cylindrical shell of radius 6.0 cm carries a uniform surface charge density sigma = 12 nC/m^2. The electric field at r = 5.9 cm is approximately a.0.81 kN/C b.zero. c.1.3 kN/C. d.12 kN/C. e.0.56 kN/C...
  12. S

    Spheres, Plates, and Gauss' Law

    Homework Statement A sphere of radius 8.0 cm carries a uniform volume charge density rho = 500*10^-9 C/m^3. What is the electric field at r = 3.0 cm? a.36.0 N/C b.230 N/C c.140 N/C d.565 N/C e.450 N/C Homework Equations E = (k*Q*r)/(R^3), where...
  13. S

    Spherical Shells and Gauss' Law

    Homework Statement A small, insulating, spherical shell with inner radius a and outer radius b is concentric with a larger insulating spherical shell with inner radius c and outer radius d. The inner shell has total charge q distributed uniformly over its volume, and the outer shell has...
  14. R

    Solve Gauss' Law Problem: Electric Flux Hemisphere

    Hello, everyone. I hope that you can help me get started on one of the problems I have due this week. Homework Statement Find the electric flux through the hemisphere z = (square root of a^2 - x^2 - y^2). - The Attempt at a Solution I'm fairly certain I need Gauss' law to help...
  15. J

    How Does Gauss' Law Apply to Non-Zero Electric Flux in a Rectangular Box?

    Homework Statement A charge Q is located inside a rectangular box. The electric flux through each of the six surfaces of the box is: Φ1=+1500 Φ2=+2200 Φ3=+4600 Φ4=-1800 Φ5=-3500 Φ6=-5400. (unit: N x m^2/C) What is Q?Homework Equations ΦE =Q/ε The Attempt at a Solution Add up all the Φ's to...
  16. S

    Easy gauss' law question that I wanna make sure I didn't make too easy

    A sphere of radius a has its center at the origin, and has charge density p=Ar^2 another sphere of radius = 2a is concentric with the first. Find the flux SE*da through the larger sphere, where that's the surface integral of E dot da, like usual. It'd just be Qin/e where e is that constant...
  17. S

    Gauss' Law and a uniform surface charge

    Use Gauss' Law to find the field inside and outside a long hollow cylindrical tube which carries a uniform surface charge sigma. It has been a few months since i did this so i may be a bit rusty As i can recall if there is a point inside a holow cylindrical tube there is no enclosed charge...
  18. D

    Solving Gauss' Law: Find Flux of 443C Ball with 7.97cm Radius

    How would you solve this: A small charge of 443 C is at the center of a 7.97 cm radius ball. How much flux passes through the ball's surface? The answer is 4.922 E-8 N.m2/C I don't know how to get this answer. Please explain. Thank you!
  19. M

    Understanding Gauss' Law: Electric Field of an Infinite Slab of Charge

    For this problem I am giving the following: An infinite slab of charge parallel to the yz plane whose density is given by: p(x)= t, -b<x<b; 0, |x|>b; Where t and b are constants. And I am to find the electric field. I am pretty confused on how to do this problem. I know that the...
  20. P

    Gauss' Law: Discrete vs Continuous Charges

    why is it that a gaussian surface cannot pass through discrete charges ... but can pass through a continuous charge distribution??
  21. B

    The Electric Flux through a Cube with a Uniform Electric Field

    I got a cube withe edge length 1.4m and has a uniform electric field, i have to find the electric flux throught the right face for the following fields. A) 2.00i B)-3.00j answer for a) is 0, i think because its uniform and all the inward and outward contribuitions cancel but then why...
  22. K

    Electrostatic equilibrium and Gauss' law

    A conducting spherical shell of ineer radius a and outer radius b carries a net charge Q. A point charge q is placed at the center of this shell. Determine the surface charge densit on (a) the ineer surface of the shell and (b) the outer surface of the shell. I'm not sure of my reasoning...
  23. P

    How Does Gauss' Law Apply to Spherical Charge Distributions?

    A charge of 2pC is uniformly distributed throughout the volume between concentric spherical surfaces having radii of 1.3 cm and 3.3 cm. What is the magnitude of the electric field 1.8 cm from the center of these surfaces? Answer in units of N/C. I used the equation \Phi = E*4\pi r^2 and...
  24. M

    Calculating Electric Field for Infinite Plane Slab with Uniform Charge Density

    Problem: An infinite plane slab, of thickness 2d carries a uniform charge density rho. Find the electric field as a function of y, where y=0 at the center. Plot E versus y calling E positive when it point in the +y direction and negative when it points in the -y direction. Okay, so I worked...
  25. G

    Why Does Gauss' Law for Magnetism Apply to Current-Carrying Wires and Squares?

    I am trying to answer all the odd problems at the end of the chapter and I can't seem to get one of them. A long, current-carrying wire is oriented vertically; next to it is drawn a square whoe area lies in the same plane as the wire. Using the distances indicated, find the magnetic flux...
  26. D

    Gauss' Law and magnitude of the electric field

    A long, nonconducting, solid cylinder of radius 4.5 cm has a nonuniform volume charge density that is a function of the radial distance r from the axis of the cylinder, as given by \rho = A r^2, with A = 3.0 \mbox{ }\mu C/\mbox{m}^5. (a) What is the magnitude of the electric field at a...
  27. U

    What are the Electric Field Lines and Flux in Coaxial Cables?

    I don't really understand Gauss' law - any help with this question would be appreciated? Coaxial cables are made of a copper wire in the center and a concentric cylindrical shell of copper outside, with insulating material in between and outside the shell. The charge per unit length of the...
  28. M

    Solving E-Fields using Gauss' Law: Choosing Surfaces

    I wonder if i could compute resultant E-fields using Gauss' law and finding the field from the flux. I have a few difficulties, the first is of course, finding the E-field from the flux and the second is regarding the closed surface. how should i choose what surface to use, especially if the...
  29. J

    Proof of Coulomb's Law using Gauss' Law

    I'm trying to derive the vector field \vec{E} = \frac{1}{4\pi\epsilon_0}\frac{q\vec{r}}{r^3} surrounding a point charge, starting with \oint_S \vec{E} \cdot \mathrm{d}\vec{A}. My uneducated guess would be to get the magnitude of the electric field from gauss' law, then integrate to get the...
  30. M

    Applying gauss' law to planar symmetry, finding E question

    I'm looking at how you find E in a Nonconducting sheet. It all makes sense until the last part. Visualize a thin, infinite, nonconducting heet with a uniform positive surface charge density \delta . A sheet of thin plastic wrap, uniformily charged on one side, can serve as a simple model...
  31. T

    Is Gauss' Law Wrong? Evidence & Explanation

    undefinedundefinedundefinedSuppose there is a charged HOLLOW CONDUCTOR in an Electric-field-free region. Since there is no electric field acting on that conductor, thus all the electric charges will distribute themselves on the surface, as predicted by Gauss’ law. Gauss’ law can be interpreted...
  32. H

    Gauss' Law & 2 Charged Cylinders

    Hi, could someone offer some advice on the following problem: ===== Q. Using Gauss' law, obtain expressions for the electric field and potential in the space between two thin, hollow, concentric conducting cylinders, of radii a and b, with the outer cylinder connected to earth ===== I...
  33. R

    Solving for Electric Field with Gauss' Law

    I have to find the electric field everywhere using Gauss’ law in differential form. Charge density is \rho = \rho_{0}r^{3} for a<r<b and 0 otherwise in spherical symmetry and then in cylindrical coordinates \nabla \cdot D=\rho I have look for D and then just get E = D/epsilon. D is where...
  34. J

    Gauss' Law in Dielectrics Part II

    OK I just want to start from the beginning and try to get the first part of this problem so I can get what is going on in my head and understand it. Here's the problem: A point charge q is imbedded in a solid material of dielectric constant K. A) Use Gauss's law as stated in equation...
  35. J

    How Does Gauss's Law Apply to Dielectrics with Embedded Point Charges?

    This problem is also giving me a lots and lots of trouble, and I don't even know where to begin. A point charge q is imbedded in a solid material of dielectric constant K. A) Use Gauss's law as stated in equation \oint{K \vec{E} \cdot \vec{A}} \;=\; \frac{Q_{free}}{\epsilon_{0}} to find...
  36. A

    How Do I Solve These Gauss' Law Problems for a Cylindrical Shell?

    I'm stuck on two problems. I hope someone can help me. Here they are... 1) For 1a I thought Q would be Q=\rho \pi L (b^2-a^2) but since \rho=\frac{k}{r} so Q=\frac {k \pi L (b^2-a^2)}{r}. After being stumped on 1a I'm not sure how to go about 1b. 2) I've derived about 4 equations for this...
  37. S

    Calculating Electric Flux Through a Square: Is Gauss' Law the Only Method?

    This is SUPPOSED to be easy but i seemingly find find it hard... A poin charge of +Q is places a distance d/2 above the centre of a square surface of side d. Find the electric flux through the square. so i know that E dA = EA (because the flux through the square is all at 90 degree...
  38. Cyrus

    Charge Distribution on a Sphere: Exploring Gauss' Law

    Hello, Question again. If we have a conductor, then according to Gauss, all the charged particles will migrate to the surface where they are furthest away from each other. This seems to make logical sense. But what if I have a charged sphere and now every particle on the surface of the...
  39. K

    What Is the Electric Field Near Charged Objects?

    I need some guidance if anyone can help me! 1. A small cube of volume 8.0 cm^3 is .30 cm from a metal sphere that has charge 2.00uC. If the cube is empty, what is the total flux through it? I tried finding the flux of the sphere as if it was a point charge but I don't know where to go...
  40. J

    Quick question regarding gauss' law

    A long coaxial cable consists of an inner cylindrical conductor with radius a and an outer cylindrical shell of inner radius b and outer radius c. The cylindrical shell is mounted on insulating supports and has no net charge. The inner cylinder has a uniform positive charge per unit length...
  41. D

    Solving Gauss' Law Problem with J.J. Thomson Model of Hydrogen Atom

    I'm having trouble with the following problem: An early (incorrect) model of the hydrogen atom, suggested by J.J. Thomson, proposed that a positive cloud of charge +e was uniformly distributed throughout the volume of a sphere of radius R, with the electron an equal-magnitude negative point...
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