What is Gauss's law: Definition and 380 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. T

    Calculating Gravitational Potential Using Gauss's Law for a Thin Rod

    Homework Statement Calculate the gravitational potential due to a thin rod of length l and mass M at a distance R from the center of the rod and in a direction perp. to the rod. Homework Equations integral form of Gauss's law wrt gravitation The Attempt at a Solution Can I use...
  2. JimiJams

    Gauss's Law conductor Problem

    Homework Statement An initially neutral conductor contains a hollow cavity in which there is a +100nC point charge. A charged rod transfers -50nC to the conductor. Afterward, what is the charge (a) on the inner wall of the cavity wall, and (b) on the exterior surface of the conductor...
  3. F

    What is my book trying to say? Is it contradicting itself with Gauss's Law and Flux?

    Homework Statement My book says Now here is the thing I have two situations (1) Consider a hollow conducting sphere with a net charge +Q and a conducting solid sphere with a net charge -Q. The solid one is inside the hollow conducting sphere. If I were to construct a Gaussian...
  4. B

    Advanced Gauss's Law Question

    A solid sphere of radius R has a non-uniform volume charge density \rho(r) and a constant surface charge density \sigma. If the field inside the sphere is uniform and radially atuned, and the field a distance 2R away from the center is zero, find \rho and \sigma in terms of R, r (distance from...
  5. M

    Understanding Gauss's Law: Solving with Correct Sign and Direction

    I know what formula you need to solve this problem (the attachment), but I'm having trouble with understanding the signs and direction of points A,B, and C. I know that the lines go towards the negative and away from the positive, but I'm still not seeing the correct signs. For instance I...
  6. B

    Solve Gauss's Law: 8.0 & -4.9 Charges in Uncharged Sphere

    Homework Statement A 8.0 charge and a -4.9 charge are inside an uncharged sphere. What is the electric flux through the sphere? Homework Equations It says in the book that Electric flux = E(4piR^2) although I do not know the radius and yet still don't believe that's the way to go to...
  7. A

    Gauss's Law with NONuniform E field

    Homework Statement A closed surface with dimensions a = b = 0.400 m and c = 0.800 m is located as shown in the figure below. The left edge of the closed surface is located at position x = a. The electric field throughout the region is nonuniform and given by E = (2.70 + 2.20 x2)i N/C, where x...
  8. A

    How Does Charge Q Affect Electric Flux Through a Hemisphere?

    Homework Statement A particle with charge Q is located immediately above the center of the flat face of a hemisphere of radius R as shown in the figure below. https://www.webassign.net/serpop/p19-33.gif (a) What is the electric flux through the curved surface? (Use any variable or...
  9. P

    Calculating Electric Field at Lead-199 Nucleus with Gauss's Law

    Homework Statement Determine the magnitude of the electric field at the surface of a lead-199 nucleus, which contains 82 protons and 117 neutrons. Assume the lead nucleus has a volume 199 times that of one proton and consider a proton to be a sphere of radius 1.20 10-15 m. Homework...
  10. Vyse007

    Gauss's Law with electric flux density

    I am taking a course in Electromagnetic Wave Theory, and the prescribed book for us is Engineering Electromagnetics by William Hayt. The book if excellent, till I reached the part about Gauss's Law. I will be describing my queries here, kindly help me out with them. 1) The book first states...
  11. I

    A question regarding the Gauss's Law

    Hi I have some questions about the Gauss's law for electric field. Wikipedia definition says Now how did Mr Gauss arrive at this conclusion regarding any closed surface ? That is a very general statement. And during his time, were there instruments which could have lead to the formulation of...
  12. R

    Gauss's Law - A hollow sphere with inner and outer radius

    Gauss's Law - A hollow sphere with inner and outer radius! Homework Statement A spherical shell of inner radius R1 and outer R2 carries a charge Q that is uniformly distributed throughout its volume. No other charges present. a)calculate E inside the sphere b)within the volume c)outside...
  13. R

    Gauss's Law - Cube with point charge at centre

    Homework Statement a)A charge Q=10nC is placed at the origin, which is the centre of a cube with side lengths a=1cm whose faces are perpendicular to the x,y and z axis. What is the total flux through the box and what is the average of the perpendicular component of the electric field on the...
  14. A

    Net Flux through a sphere (Gauss's Law)

    Homework Statement Find the net electric flux through the spherical closed surface shown in the figure below. The two charges on the right are inside the spherical surface. (Take q1 = +1.96 nC, q2 = +1.03 nC, and q3 = -3.09 nC.) https://www.webassign.net/serpse8/24-p-006-alt.gif The...
  15. F

    Gauss's Law and a hollow metal cylinder

    Homework Statement A long, straight wire is surrounded by a hollow metal cylinder whose axis coincides with that of the wire. The wire has a charge per unit length of lambda, and the cylinder has a net charge per unit length of 2lambda. From this information, use Gauss's law to find (a) the...
  16. R

    Gauss's Law and electric flux

    Can someone please help me work through this problem I've spent over an hour on this trying to figure out what to do.. here's the question A nonuniform electric field is given by the expression E = ay^i + bz^j + cx^k, where a, b, and c are constants. Determine the electric flux through a...
  17. F

    Why is this 0? Help Gauss's law

    Homework Statement A long straight metal rod has a radius of 5.00cm and a charge per unit length of 30.0nC/m. Find the electric field a) 3.00cmThe Attempt at a Solution It says a) = 0 I did some math and I got 2k\frac{\lambda}{r} The rod is solid, so should a E-field be radially outward...
  18. L

    Using Gauss's Law to determine an electric field

    Homework Statement Homework Equations {\phi} = \int E dA = \frac{QL}{\epsilon_0} The Attempt at a Solution I'm aware of the definition of Gauss's law of electrostatics (however evidently I'm not very good at applying it), but I can't seem to fully answer the rest of the question...
  19. Z

    Solve Gauss's Law Problems: q, E, ΦE

    Homework Statement 1) A point charge is placed at the centre of a spherical Gaussian surface. Is ΦE changed, a) if the surface is replaced by a cube of the same volume? b) if the charge is moved off centre in the original sphere, still remaining inside? 2) A point charge q is placed at the...
  20. A

    Why is the flux on top and bottom of a cylinder ignored in Gauss's law?

    Homework Statement (first of all, let me know if I am wrong in any parts) gauss's law can be used on cylinder. Why is it that flux on top and flux on bottom of the cylinder, with area pi*r^2 ignored? (aka, equal to 0) such that Flux= Integral(E*da)=E2(pi)rl=q/(Eo) where (Eo) is permitivity...
  21. I

    Solv Gauss's Law Questions | Zack's Search

    I was searching the forums and I found someone asking the same question a while back, but i am totally confused, I thought I was understanding this stuff up to this point. http://answers.yahoo.com/question/index?qid=20100928212107AAwXTlT&r=w I posted and wrote up the whole problem on...
  22. W

    Is Zero Electric Field on a Closed Surface Indicative of No Net Charge?

    QUESTIONS 5.The electric field E is zero at all points on a closed surface; is there necessarily no net charge within the surface? If a surface encloses zero net charge, is the electric field necessarily zero at all points on the surface? 6.Define gravitational flux in analogy to electric...
  23. P

    Electric fields and Gauss's Law

    Negative charge - Q is distributed uniformly around a quarter-circle of radius a that lies in the first quadrant, with the center of curvature at the origin. Find the x-component of the net electric field at the origin. Find the y-component of the net electric field at the origin.
  24. S

    Electric Field from Charge Densities: Gauss's Law

    There are basically three types of charge densities; linear \lambda (over a thin ring or rod), surface \sigma over a thin flat surface, and over a volume \rho The problem is how these densities produce an electric field: applying Coulomb's law for the electrostatic force using appropriate...
  25. T

    Doubt about differential Gauss's law

    We know that the Gauss's law expressed in the differential form is: \mathbf{\nabla}\cdot\mathbf{E} = \frac{\rho}{\epsilon_0}, right? I read at wikipedia that \rho is: the total charge density including dipole charges bound in a material. I don't understand... The left side of...
  26. M

    What is the significance of the charge density in Gauss's law?

    So I'm reading Div, Grad, Curl and All That which is my only exposure to Maxwell's equations. The author started with the integral form of Gauss's law (which I get), where the surface integral of the electric field = the enclosed charge (q) divided by epsilon nought. But in deriving the...
  27. A

    Coulomb's vs Gauss's Law: What's the Difference?

    What is the difference between coulomb's law and gauss's law ? because both are giving same results while calculating electric fields ? what is the basic difference. are they same?
  28. Y

    Gauss's Law and a long thin wire

    Homework Statement A long thin wire, hundreds of meters long, carries a uniformly distributed charge of -7.2 microCoulombs per meter of length. Estimate the magnitude and direction of the electric field at points (a) 5.0 m and (b) 1.5m perpendicular from the center of the wire. Homework...
  29. I

    When should the integral be used for Gauss's law?

    I have difficulty when trying to decide which form of Gauss's law I should use for a problem. Please, tell me when I should use the integral form: \int E \cdot dA = \frac{Q_{in}}{\epsilon_{0}} and when it's appropriate to use the other form: E \cdot A = \frac{Q_{in}}{\epsilon_{0}}
  30. T

    Gauss's Law: Field of a line charge and cylinder

    1. Homework Statement A long, thin straight wire with linear charge density \lambda runs down the center of a thin, hollow metal cylinder of radius R. The cylinder has a net linear charge density 2(\lambda). Assume \lambda is positive. Find expressions for the magnitude of the electric...
  31. G

    Gauss's Law and Superposition of Fields

    Gauss's Law and Superposition of Fields (edited again, something else wrong) Homework Statement Right. The shape itself has charge Q, so it has charge density \frac{Q}{\frac{4}{3} \pi R^3 - \frac{4}{3} \pi (\frac{R}{2})^3} = \frac{6Q}{7\pi R^3} Let's call this \rho. If it were filled in...
  32. S

    Finding the Value of b in Gauss's Law Charge Problem

    Homework Statement The box-like Gaussian surface of the attached figure encloses a net charge of +24.0 \epsilon_0 \mu C and lies in an electric field given by \vec E = [(10.0 + 2.00x) \hat i - 2.00 \hat j + bz\hat k]N/C with x and z in meters and b a constant. The bottom face is in...
  33. K

    Electrostatics (Gauss's Law)

    Homework Statement A thin metallic spherical shell contains a charge Q on it. A point charge q is placed at the centre of the shell and another charge q1 is placed outside it. All the three charges are positive. Find (a) the direction of the force on the charge at the centre, and (b) the...
  34. F

    When to Use Gauss's Law and Coulomb's Law for Calculating Electric Field?

    When should I use one and when should I use the other? For example, suppose I have a rod of length 2L, with an edge on the point -L on the X axis and another on L. The rod is uniformly charged, with total charge Q>0. having that said, if i wanted to calculate the electric field in an arbitrary...
  35. C

    Using Gauss's law to determine elctric fields (Calculus based problem)

    Homework Statement A sphere of radius R has a total charge +Q, uniformly distributed throughout its volume. It is surrounded by a thick spherical shell of inner radius R and outer radius 2R carrying a total charge -Q, also uniformly distributed throughout its volume. Using Gauss's law...
  36. O

    Electric charge on hollow spherical conducting shells Gauss's Law(?)

    There are two spherical hollow conducting shells, one inside the other. The outer shell has a radius 4 times that of the inner shell. There is a switch connecting the two shells, which is for the moment, open. Both shells have a positive charge (inner shell = +20nC and outer shell = +60nC...
  37. D

    Proof of Gauss's law using coulomb's law

    so my book has a point charge q inside an arbitrary surface S and at a point P on the surface S, the electric field is E = q/4(π)(ε0)(r2). so the flux through S is then dΦ = E * dS = q/4(π)(ε0)(r2) * dS = q/4(π)(ε0) * dScosθ /(r2) = q/4(π)(ε0) * dΩ. then my book takes the integral of both sides...
  38. C

    Gauss's Law - electric flux through a spherical shell

    Homework Statement A spherical shell of radius 4 m is placed in a uniform electric field with magnitude 7020 N/C. Determine the total electric flux through the shell. Answer in units of N · m^2/C. Homework Equations Gauss's Law The Attempt at a Solution I thought this would be as simple as...
  39. M

    Gauss's Law and Finding the electric field

    [b]1. Two long charged, concentric cylinders have radii of 3.0 and 6.0 cm. The charge per unit length is 5.0 x 10-6 C/m on the inner cylinder and -7.0 x 10-6 on the outer cylinder. Find the electric field at (a) r = 3.0 cm and (b) r = 8.0 cm, where r is the radial distance from the common...
  40. K

    Experimental evidence of Gauss's law in electrodynamics?

    In electrostatic case, Gauss's law can be derived from Columb's law, so we can regard experimental evidence for Columb's law as evidence of Gauss's law. But what about non-static case? In this case we know columb's law is no longer valid, so we need experimental evidence to justify Gauss's law...
  41. L

    Gauss's law, cylinder of length L

    http://img404.imageshack.us/img404/4148/gauss3j.png (infinitly long) \Phi=\Phi_{0}(1-{r \over R}) {C \over m^2} What's the charge of the cylinder of length L? Again, almost everything was wrong...
  42. S

    Calculating Electric Field: Gauss's Law with Uniformly Distributed Charge

    Homework Statement A charge of 9 pC is uniformly distributed throughout the volume between concentric spherical surfaces having radii of 1.8 cm and 3.8 cm. Let: Ke = 8.98755 × 109 N · m2/C2 . What is the magnitude of...
  43. L

    Proving Gauss's Law for Magnetism

    As you probably know, there is a formal proof of Gauss's Law for electric fields based on Coulomb's Law and the concept of solid angles. How can one prove Gauss's Law for magnetic fields? Is there a similar proof based on solid angles?
  44. S

    Net Electrostatic Force on Four Charges at the Corners of a Square

    Homework Statement There are four charges, each with a magnitude of 3.04C. Two are positive and two are negative. The charges are fixed to the corners of a 0.124-m square, one to a corner, in such a way that the net force on any charge is directed toward the center of the square. Find the...
  45. L

    Understanding Gauss's Law and Solving for E(P) and phi(P)

    http://www.twiddla.com/188165 R and Q are given E(P)=? phi(P)=? The Attempt at a Solution Homework Statement Homework Equations I have no idea. I managed to do phi=E*2pi*r*h
  46. K

    Electric Field Involving Gauss's Law Problem

    Homework Statement An atom that has Z protons, each with positive charge of magnitude e, reside in the nucleus at the center, surrounded by a uniformly distributed spherical cloud of radius R consisting of Z electrons, each with negative charge magnitude e, centered on the nucleus e. Use...
  47. K

    Gauss's Law, electric field of sphere

    Q: A nonconducting sphere of radius 10.00 cm carries a uniform volume charge density ρ = 410 nC/m3. (a) What is the total charge of the sphere? 1.717 nC Find the electric field at the following radii. (b) r = 2.10 cm _____N/C (c) r = 9.90 cm _____kN/C (d) r = 10.10 cm...
  48. N

    Find Earth's charge using Gauss's Law

    Homework Statement The electric field just above the surface of Earth has been measured to typically be 163 N/C pointing downward. What is the total charge on Earth's surface implied by this measurement? Homework Equations ∫EdA = Qinside/ɛo The Attempt at a Solution I...
  49. N

    What is Gauss's Law for a Concentric Cable?

    Homework Statement The figure below shows a portion of an infinitely long, concentric cable in cross section. The inner conductor has a linear charge density of λ = 6.10 nC/m and the outer conductor has no net charge. http://www.webassign.net/tipler/23-36alt.gif (a) Find the electric field...
  50. M

    Electric Field Strength of 10cm x 10cm Charged Copper Plate

    A thin, horizontal 10 cm x 10 cm copper plate is charged with 1.0 x 10^10 electrons. If the electrons are uniformly distributed on the surface, what is the strength of the electric field? I initially went to use the formula given in the text for a conductor where Electric field=n/Eo...
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