2.1 Conductor, photoconductor, semiconductor, superconductor and insulator(dielectrics 2.1.1 The definitions Conductor is the material inside which charges can flow freely(metals) Insulator is the material that does not readily transport charges (Ceramics Semiconductor is the material with conductivity in the between (Si, Ge Photoconductor is a poor conductor in dark but good conductor with light (selenium) Superconductor is material with infinitive conductivity below critical 2.1.2. The characters of conductor at stationary field 1)Equal-potential surface: E=0, therefore, V=Const 2)Zero charge density inside the conductor E=0, from Gauss theorem, therefore, p=0 3 Charge of conductor only distribute on the surface from gauss theorem e=o/8 4 E must be normal (relationship between the curvature and density) 2.1.3 Applications of the above characters ) Use the conductor to design the desired electric field Of course you may use the charges distribution to do the same but that is not easy in most situations
2.1 Conductor, photoconductor, semiconductor, superconductor and insulator（dielectrics) Conductor is the material inside which charges can flow freely. (metals) Insulator is the material that does not readily transport charges. (Ceramics) Semiconductor is the material with conductivity in the between. (Si, Ge) Photoconductor is a poor conductor in dark but good conductor with light (selenium) Superconductor is material with infinitive conductivity below critical T . 2.1.1 The definitions 2.1.2. The characters of conductor at stationary field 1) Equal-potential surface: E=0, therefore, V=Const. 2) Zero charge density inside the conductor: E=0, from Gauss theorem, therefore, ρ=0 3) Charge of conductor only distribute on the surface, from gauss theorem , 0 E = / 2.1.3 Applications of the above characters 1) Use the conductor to design the desired electric field Of course you may use the charges’ distribution to do the same, but that is not easy in most situations. 4） E must be normal (relationship between the curvature and density)
Electrostatic lens 2)Van de Graaff generator 3)Electrostatic shielding 4)Thunder-lighting arrestor Belt
Electrostatic lens 2) Van de Graaff generator 3) Electrostatic shielding 4) Thunder-lighting arrestor
2.1.4 Superconductor(aluminum, tin, lead, Zinc, indium etc. R(9) TABLE 27.3 Critical 0.15 Temperatures for Various Superconductors 0.125 Material T(K) 0.10 NbaGe 23.2 Nb.Sn 18.05 0.075 Nb 9.46 Pb 7.18 0.05 Hg 4.15 Sn 3.72 0.025 Al 1.19 0.88 YB 92 4.04.1424.344 Bi-Sr-Ca-Cu-O 105 T(K) Tl-Ba-Ca-Cu-O 125
2.1.4 Superconductor (aluminum, tin, lead, zinc, indium etc.)
2.1.5 Photoconductor The principle of copy machine(Xerography) 硒? + +++ ++ ++ (b) selenium +
2.1.5 Photoconductor The principle of copy machine (Xerography) 硒？ selenium
2.1.6 Semi-conductor(to be studied) 2.1.7 Insulator(dielectrics 2.2 Capacitance 2.2.1 Defination C=Q/V 1)Capacitance is the capacity of a body to keep electric charge 2)It is always positive 2.2.2 The unit Faraday, 1F=1Co/1V 2.2. 3 The capacitance of an isolated spherical conductor C==4兀ER 2. 2. 4 Parallel plate capacitor Ilustration: A parallel-plated capacitor consists of two parallel plates with a separation much smaller than the area. the plates carry equal and opposite charges Edge effect can be neglected
2.1.6 Semi-conductor (to be studied) 2.1.7 Insulator (dielectrics) 2.2 Capacitance 2.2.1 Defination: C=Q/V 1) Capacitance is the capacity of a body to keep electric charge 2) It is always positive 2.2.2 The unit : Faraday , 1F=1Co/1V 2.2.3 The capacitance of an isolated spherical conductor R V Q C = = 4 0 2.2.4 Parallel plate capacitor Illustration: A parallel-plated capacitor consists of two parallel plates with a separation much smaller than the area. The plates carry equal and opposite charges. Edge effect can be neglected :