PhysThetutorialforCh23章节幻灯片.pptVIP

Key words Electric field lines Electric flux Gauss’s Law Gaussian surface Electrostatic shielding Insulating sphere Conductor Cube Cylinder Cylindrical symmetry Spherical symmetry Planar symmetry Coaxial Concentric GAUSS’S LAW electric flux (电通量): Gauss’ law : Very useful when the charge distribution has spherical, cylindrical or planar symmetry Select the appropriate closed, imaginary Gaussian surface. For spherical symmetry (对称), use a concentric (同心) spherical surface For cylindrical symmetry, use a coaxial (同轴) cylindrical surface with flat ends perpendicular to the axis of symmetry For planar symmetry, use a cylindrical surface with its flat ends parallel to the plane + Problem-solving strategy Uniform + charged conducting sphere Uniform + charge insulating sphere For E inside the sphere, r R Volume charge density ρ : Total charge enclosed by the Gaussian surface : By Gauss’ Law : → Positive charge Q is distributed uniformly throughout the volume of an insulating sphere of radius R. Find the magnitude of the E-field at a point P a distance r from the center of the sphere For E inside the sphere, r R For E outside the sphere, r R Sketch the graph of E vs r E r R Uniform + charge insulating sphere Two Uniform + charge conducting Plates Separate conducting plate Arranged two conducting plate Problem 1 A conducting spherical shell with inner radius a and outer radius b has a positive point charge Q located at its center. The total charge on the shell is -3Q, and it is insulated from its surroundings. Derive expressions for the E-field magnitude in terms of the distance r from the center for the regions r a, a r b and r b What is the surface charge density on the inner surface of the conducting shell? What is the surface charge density on the outer surface of the conducting shell? 4. Sketch the electric field lines and the location of all charges. 5. Graph the E-field magnitude as a function of r Problem 1 Problem 1 Problem 2 A small conducting spheri