23. Electrostatic Energy amp; Capacitors静电能和电容器课件.ppt

23. Electrostatic Energy Capacitors 靜電能和電容器 Electrostatic Energy 靜電能 Capacitors 電容器 Using Capacitors 使用電容器 Energy in the Electric Field 電場中的能 精品文档 The lifesaving jolt of a defibrillator requires a large amount of energy delivered in a short time. 除纖顫器救命的電擊需要在短時間內送出大批能量。 Where does that energy come from? 這些能量從何而來？ Capacitor 電容器 精品文档 23.1. Electrostatic Energy 靜電能 Electrostatic Energy = work done to assemble the charge configuration of a system. 靜電能 = 裝組系統的電荷配置所需做的功。 Reference 參考 ( 0 energy 能): when all component charges are widely separated. 當所有的組分電荷都相隔甚遠時。 Bringing q1 in place takes no work. 把 q1 歸位不需做功 Bringing in q2 takes 把 q2 歸位需功 Bringing in q3 takes 把 q3 歸位需功 Total electrostatic energy 總靜電能 精品文档 23.2. Capacitors 電容器 Capacitor: pair of conductors carrying equal but opposite charges. 電容器：帶著等量異性電荷的一對導體。 Usage: store electrical energy 用途：存儲電能 Parallel-Plate Capacitor 平行板電容器: 2 conducting plates of area A separated by a small distance d . 兩塊相隔短距離 d ，面積為 A 的導體板。 Plates are initially neutral. 開始時兩塊板都是中性。 They’re charged by connecting to a battery. 接上電瓶後起電。 Charge transfer ? plates are equal but oppositely charged. 電荷轉移 ? 兩塊板的電荷量等而性異。 Large A, small d ? E ? 0 outside. 大 A ，小 d ? 器外的 E ? 0 。 Far from the edges 離邊遠處 精品文档 Capacitance 電容量 Parallel-plate capacitor: 平行板電容器： ? C = Q / V = capacitance 電容量 Parallel-plate capacitor 平行板電容器 See Probs 參閱習題 41 42 Practical capacitor ~ ?F ( 10?6 F) or pF ( 10?12 F ) 實用電容器 Charging / Discharging 充 / 放電 精品文档 Energy Stored in Capacitors 存在電容器內的電能 When potential difference between capacitor plates is V, 電容器兩板之間的電位差為 V 時， work required to move charge dQ from ? to + plate is 把電荷 dQ 從 ? 移至 + 板需作功 Work required to charge the capacitor from 0 to V is 把電容器從 0 充電至 V 需作功 = U = energy stored in capacitor 存在電容器內的電能 Note 注意: In a “charged” capacitor, Q is the charge on the + plate. 在一個”帶電”的電容器內，Q 是 + 板上的電荷。 The total charge of the capacitor is always zero. 電容器的總電荷永遠為