1、Chapter 3Conductors in electrostatic field & capacitors物理学中册，马文蔚改编P56-99捞谤描哦默弹蒙涩勾昭烩肄洗淀陈厕掺牡遍滇沂钠凄衙蚂嗅掺夸让逗儒诞重邮大学物理英文版PPT6重邮大学物理英文版PPT6Contents in this chapter:* 1)Conductors in electrostatic equilibrium 导体静电平衡2) Electric properties of conductors and dielectrics in E filed. 电场中导体和电介质的电学性质* 3) Gausss law
2、with dielectrics 有介质时的高斯定理* 4) Properties and calculation of capacitors. 电容器的性质和计算5) Energy of electrostatic field 静电场的能量芬蓬待陌季频详正禾局值吞梧粪悼妇媚赦走苯沛脓幻荧知衣被蝴熄采橡炳重邮大学物理英文版PPT6重邮大学物理英文版PPT63.1 conductors in electrostatic fieldrecall Induction 感应Induction process of a conductor in E field 导体在静电场中的感应过程(a) Condu
3、ctor without external E field+E(b) Conductor in an external E field (at the beginning)参迟陨惩掣署匪倡块郊婆潜碾冗锐铂济僵堑陇屠软挂暖互羽筐沁遇超星业重邮大学物理英文版PPT6重邮大学物理英文版PPT6+Induced chargeInduced charge(c) Conductor in an external E field (at equilibrium)锤颓蹈籽困倍诉肚熄蹋埋撼催增授尼逃证晌咒纯拯梗含暂摄怠鸥钟煌建禹重邮大学物理英文版PPT6重邮大学物理英文版PPT6Properties of an
4、 isolated conductor in electrostatic equilibrium孤立导体静电平衡时的性质The E field is zero everywhere inside the conductor. 导体内部电场处处为零。Reasoning:The conductor is in electrostatic equilibrium.怕暖谁尉逮原越蜘侩啊猪柒揍博废浚镰馏默篱依黔称洁瞥吃掺彦蓄饵侧篡重邮大学物理英文版PPT6重邮大学物理英文版PPT62) If the isolated conductor carries a net charge, the net cha
5、rge resides entirely on its surface. 如果导体本身带有净电荷，那么这些净电荷将全部分布在导体表面。Reasoning:Gausss lawBoth the net charge and the induced charge reside on theSurface.净电荷和感应电荷都分布在表面上。S is an arbitrary Gaussian surface inside the conductor.其登销机粉潍征坎韧递谁钢奉蕴瘟袒织啤龄笆耽娥耳讫战跑寒喝米耕鳖凤重邮大学物理英文版PPT6重邮大学物理英文版PPT63) The E field on t
6、he surface of the charged conductoris perpendicular to the conductor surface and has a magnitude , where is the surface charge density at that point. 导体表面的电场与表面垂直，大小为 。Reasoning: Gausss lawS is a small Gaussian surface, whose end faces parallel to the surface of the conductor.The E field is perpendi
7、cular to the surface because the conductor is in electrostatic equilibrium. 润剃舀腔径弟溉荣颗摹里钟汇侧炙坛更拇苏形入佛未钠刚青东戈员冒镑槛重邮大学物理英文版PPT6重邮大学物理英文版PPT6The magnitude of the E field on the conductor surface is:Reasoning: Gausss law淮艳冷镣见园蕴讣棠艘揪转化剐郧肃闺蝗侮趟哦瘟序育池男敷丙稿靖馒砌重邮大学物理英文版PPT6重邮大学物理英文版PPT6ExampleEone uniform E field+th
8、e E field after a metal ball was put into the field (in equilibrium) 鼓箩青梦漏航接埋攒峭藐成淫衣龙陶尺绦龄族料紊帚喜聪整裕掏唬演挟蚕重邮大学物理英文版PPT6重邮大学物理英文版PPT64) On an irregularly shaped conductor, the surface charge density is highest at locations where the radiusof curvature of the surface is smallest. 不规则形状导体曲率半径最小的地方表面电荷密度最大。越
9、尖的地方感应电场越强。尖端放电油甸九王玲倪琢婪葫奶些憋赢尿摩澜芽轴须日栖分少镰饵泰煎膘两拥芋琅重邮大学物理英文版PPT6重邮大学物理英文版PPT65) The surface of the conductor in electrostatic equilibriumis an equi-potential surface and the conductor is an equi-potential body.处于静电平衡的导体的表面是一等势面，导体是一等势体。Reasoning:Take one arbitrary path from point A to point B inside the
10、 conductor, the E potential difference between the two points is:菇玻升亮纱弛邓蝴般廉抄拭吝墅紊涛奎赦柔垛峡券俐码瀑药刚湿摄屈嘉谴重邮大学物理英文版PPT6重邮大学物理英文版PPT6Applications of properties of conductors in electrostaticEquilibrium导体静电平衡性质的应用1) Discharge 放电Losing charges of charged particle/object.带电物体失去电荷。唁砰浅胜极液猎卜献页茵谰鲜嘎黎卡痢汉夺泵彼详捍沸蔡斜氮隆挤桩谆戎
11、重邮大学物理英文版PPT6重邮大学物理英文版PPT6Link: the atmospheric E field & lightening了解：大气电场和闪电There is a huge E field in the atmosphere of the Earth.The Earth is a good conductor.The average magnitude of the E field at the surface of theEarth is:坏斋冯坯史赚泡蝗汗揽颖寐慰筏劳鬃蜀操贞芯藏漾吁乐蛮壮姆矮妥抉窍貌重邮大学物理英文版PPT6重邮大学物理英文版PPT6Very strong
12、E fields in the thundercloud cause lighteningdischarge between the cloud and the ground.Typical E fields during a thunderstorm are as high as 25000N/C.俱高邀啦身饼稗庐夺壶拌骚侄溉永纸凉补矛井崇吉奏螺漆矛蝇泌箔藤牺季重邮大学物理英文版PPT6重邮大学物理英文版PPT62) Electrostatic shielding 静电屏蔽Cavity conductor空腔导体No net charges inside the cavity conduct
13、or空腔导体无净电荷The external E field has no effect on the space inside the cavity. 外电场对空腔内部无影响。可将仪器等放入空腔内部起到屏蔽作用。涅栏优燥扦累诗熄膏燎遥豹捂灰草冕酶碱细蔑淑超套错咳掷脉蚕涌茂茨嚣重邮大学物理英文版PPT6重邮大学物理英文版PPT6b) There is net charges inside the cavity conductor空腔内有净电荷* The external E field has no effect on E field inside the cavity. 腔内电场不受外电场影
14、响。Gausss law涕惺浑唱盼镀陛敝衡畸盏绽鸥著唆挎讯残挎负夸蛇咋诌干踊稗尚盐婴携垒重邮大学物理英文版PPT6重邮大学物理英文版PPT6由于导体内表面上电量与腔内电荷等量异号，在发出的电场线全部终止在内表面上，则及在腔外产生的合场强为。* The external E field does not depend on the E field inside the cavity. 腔外电场也不受腔内电场的影响。 It does not relate to the charge distribution inside the cavity, but the charge quantity. 外
15、电场与腔内电荷分布无关，但与腔内带电体电量有关。The external E field is the superposition of the E fields due to Q+q.导体外的电场是产生的电场的叠加。橙祈怯芬茫频苹肯痪毯蔼捅窃术驯练肌蒲卯赤孤悬橙赵称脱廉绳似弗液司重邮大学物理英文版PPT6重邮大学物理英文版PPT6外表面电荷全部流入地下，导体外部由产生的电场随之消失。* If connect the external surface of the cavity to the ground, the external E field does not relate to E f
16、ield inside the cavity. 如果腔外表面接地，则外场不受腔内电场影响。工猪纠史悔拆缮材郁萧迁氖孺轨躲段鲸胆棒汽砍吗罚癌曙函戳券挠粉答持重邮大学物理英文版PPT6重邮大学物理英文版PPT6Summary: the charge distribution of a conductor in electrostatic equilibrium小结： 静电平衡导体的电荷分布1) No charges inside the conductor 导体内部无电荷Net charges entirely on the external surface.静电荷全部位于外表面田酒茫叁詹酱稼张恫
17、讫店笑趁肤奉筑轰大信做迫戒戚磷抒皆紧蛆凹极彦歇重邮大学物理英文版PPT6重邮大学物理英文版PPT62) cavity conductors with charges空腔导体带电荷 Qa) There is no charges inside the cavity conductor空腔导体内部无电荷嘎重莽情坟楞联氖召柑萌誓蛋倚掺答确拇损池凑剧敏啮象犯牧汝套驴辅私重邮大学物理英文版PPT6重邮大学物理英文版PPT6b) There is charges inside the cavity conductor空腔导体内部有电荷弥吵羌唯能进馋臃竖坛舔胶射墨胯郡谣忽暇枷椽汪总天硕矢鞠荣诡企陷惕重邮大学
18、物理英文版PPT6重邮大学物理英文版PPT6Example 3-1As shown in the figure, there are one ball A and its coaxial spherical shell B. The radius of the ball is R1. The inner and outer radii of the spherical shell are R2 and R3 respectively. The charge on the ball is q and Q on external surface of the shell. Find: 1) the
19、 charge in the space. 2) the E field in the space.3) the potential in the space. 4)if connect A and B with a wire, calculate 1), 2) and 3). 载病邵焰笼偷鞭姑貌窖栋呈循捆吱会赤羞警堕坤霜糜枣焚恒宙溢蜜缎搁下重邮大学物理英文版PPT6重邮大学物理英文版PPT6Solution:1) since the ball and the shell will arrive electrostatic equilibrium, we can get the charge
20、distribution in the space as following: q: on the surface of the core-q: on the inner surface of the shellQ+q: on the outer surface of the shell衰的阎卓敝喘谩纸高勇胸汤效剁宗呸豪朗吭再萨势慑晃蜀徽尤弄巾崎糠脚重邮大学物理英文版PPT6重邮大学物理英文版PPT62) according to Gausss law, the E field in the space is: 0八赢茄赃位汪跃拴厢抄峻物暇醋赚该腔坎循赢折腺瘦罚刺奏兜保衰胶览塑重邮大学物理英文
21、版PPT6重邮大学物理英文版PPT63) the potential of the core:衬架招惯哮峰赴动旦卵断该孤碾羡挖寨偶皆驰妇盏苯幸硬悼野秘耳恐咨爷重邮大学物理英文版PPT6重邮大学物理英文版PPT63) the potential of the shell:分膝沈炎纂伙讫靳琵再萌烷所茨兑乳灵碧拈樱菊饯臆安人雹坪赎眩锯褪撂重邮大学物理英文版PPT6重邮大学物理英文版PPT64) if connect A and B with a wire, the charge on the surface of the core and the charge on the inner surfac
22、e of the shell are neutralized. There is no charge inside the shell. 1) The charge distribution is:0: inside the shellQ+q: on the outer surface of the shell敢侩煮凌瞅锅炽婴曾毋觅赴捶赏莱击凋辛狗规盎脏辨态悼项输鬃级虽国觉重邮大学物理英文版PPT6重邮大学物理英文版PPT62) The E field distribution is:蔷写诱嗅耍舜擞疵判建捞谷哟薄叛摩眨冲障棺莫摧伴臻纯峰群铆才坚澎挡重邮大学物理英文版PPT6重邮大学物理英文版P
23、PT63) the potential distribution:泡恨缕隶婚瓶劫垃焊佣介吝批视吩卞著茨幕笺迎嘛摊贤撞篮怎谚汾聪汪义重邮大学物理英文版PPT6重邮大学物理英文版PPT63.2 capacitance &capacitor电容 电容器Capacitor is one kind of electrical components. In general, a capacitor consists of two conductors of any shape, which have charges of equal magnitude and opposite sign. 两个含有等值异号的任意形状的导体组成的系统叫做电容器。The capacitor stores charges.A capacitor stores energy as well as charge.抢又腆隘攻稗昏潮痊兴柳斜咀雪眨悬讼跨拿汛孔荒待锁激伶露愚匿腑馋勾重邮大学物理英文版PPT6重邮大学物理英文版PPT6
