《Fundamentals of Physics精品教学-华南理工》23 Gauss Law.pptVIP

Fundamentals of Physics 23 Gauss’ Law 23-1 A New Look at Coulomb’s Law The advantages of symmetry. Coulomb’s law is the governing law in electrostatics, but it is complicated. Gauss’ law is the equivalent of Coulomb’ s law, it takes advantage of symmetry. Central to Gauss’ law is a hypothetical closed surface called a Gaussian surface. 23-2 Flux (water, air and light) Air flux: air volume flowing through an area per unit time Flux of velocity field through a loop a vector field Fundamentals of Physics 23 Gauss’ Law 23-3 Flux of an Electric field Fundamentals of Physics 23 Gauss’ Law Flux of velocity field through a loop a vector field 23-3 Flux of an Electric field Scalar N.m2/C Fundamentals of Physics 23 Gauss’ Law A Gaussian surface in the form of cylinder of radius R immersed in a uniform electric field E, with the cylinder axis parallel to the field. What is the flux of the electric field through this closed surface? Fundamentals of Physics Sample Problem Fundamentals of Physics Sample Problem A nonuniform electric field given by E=3.0xi+4.0j pierces the Gaussian cube shown in the figure. (E is in Newton per coulomb and x is in meters.) What is the electric flux through the right face, the left face, and the top face? Fundamentals of Physics Sample Problem x Fundamentals of Physics Sample Problem x 23-4 Gauss’ Law The physical meaning of Gauss’s law Holds only in a vacuum or in air Algebraic sum of enclosed charges Fundamentals of Physics 23 Gauss’ Law Net flux is outward (+) or inward (-) The role of charges outside Gaussian surface Fundamentals of Physics 23 Gauss’ Law 23-4 Gauss’ Law The figure shows five charged lumps, an electrically neutral coin, and the cross section of a Gaussian surface S. What is net electric flux through the surface if q1=q4=+3.1 nC, q2=q5=-5.9 nC, q3=-3.1 nC? Fundamentals of Physics Sample Problem What is the net charge en