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1、 摩擦起电两种电荷-初中物理教案学案摩擦起电两种电荷教案示例 (一)教学目的 1.知道什么叫物体带电和摩擦起电。 2.知道什么实验事实使人们认识到自然界有两种电荷；知道正、负电荷是如何规定的；知道电荷间的相互作用。 3.知道验电器的构造和原理，会用验电器判断物体是否带电。 4.知道电量及其单位。 (二)教具 玻璃棒两根，橡胶棒两根，丝绸一块，毛皮一块，支架两个，验电器一个，验电一个，碎纸屑若干。 (三)教学过程 1.复习 提问(1)：日常生活中，当空气干燥时用塑料梳子梳头发，会出现什么现象？ 答：头发会随梳子“飘”起来。 提问(2)：如果我们身上穿了几件化纤毛衣，在晚上脱衣时，有时会发出响声，
2、甚至出现火花。你有过这种体会吗？你知道上面提到的两种现象发生的原因吗？ 答：摩擦起电。 教师总结：同学们在小学自然课的学习中已经了解了一些关于摩擦起电的知识。摩擦起电的现象在日常生活中又是经常可以看到的。那么，带了电的物体具有哪些性质？头发为什么会随梳子飘起来？在这一节里，我们将继续进行学习和讨论。 2.进行新课 (1)物体带电与使物体带电的方法演示实验： 用毛皮摩擦橡胶棒，然后把棒靠近纸屑，验电羽等轻小物体，观察现象。 用丝绸摩擦玻璃棒，然后将棒靠近纸屑，验电羽等轻小物体，观察现象。 我们看到，被毛皮摩擦过的橡胶棒，被丝绸摩擦过的玻璃棒，都具有了吸引轻小物体的性质。 物体具有了吸引轻小物体的
3、性质，我们就说物体带了电，或说物体带了电荷。 习惯上把带了电的物体叫做带电体。 在空气干燥的时候，用塑料梳子梳头发，头发会随着梳子飘起来，就是因为梳子带了电，能吸引头发的缘故。 使物体带电的方法： 摩擦起电 用摩擦的方法使物体带电叫摩擦起电，这种方法简单、常见。 下面请同学们举出几个日常生活中常见的摩擦起电的例子。 接触带电 除摩擦外，用接触的方法也可以使物体带电。 演示用毛皮摩擦过的橡胶棒甲接触没有被摩擦过的橡胶棒乙，然后用乙去靠近纸屑、验电羽，观察橡胶棒乙能够吸引纸屑、验电羽等轻小物体，这说明橡胶棒乙通过接触橡胶棒甲而带了电。 (2)两种电荷 我们已经知道了什么叫带电现象，知道了被毛皮摩擦
4、过的橡胶棒和被丝绸摩擦过的玻璃棒都带上了电荷，那么它们带的电荷是否相同呢？ 演示实验： 将被毛皮摩擦过的橡胶棒悬挂在支架上，用另一根被毛皮摩擦过的橡胶棒去靠近它，结果它们互相排斥。将被丝绸摩擦过的玻璃棒悬挂在支架上，用另一根被丝绸摩擦过的玻璃棒去靠近它，结果它们也互相排斥。 将被毛皮摩擦过的橡胶棒悬挂在支架上，用被丝绸摩擦过的玻璃棒去靠近它，结果它们互相吸引。 思考：这两个实验现象说明什么？ 答：被毛皮摩擦过的橡胶棒和被丝绸摩擦过的玻璃棒所带的电荷不同。 教师总结： 人们通过大量的实验研究发现，用摩擦起电的方法可以使各种各样的物质带电。带电后的 物体凡是跟丝绸摩擦过的玻璃棒互相吸引的，必定跟毛
5、皮摩擦过的橡胶棒互相排斥；凡是跟毛皮摩擦过的橡胶棒互相吸引的，必定跟丝绸摩擦过的玻璃棒互相排斥。这些事实使人们认识到自然界中只有两种电荷。 正电荷和负电荷 正电荷：指被丝绸摩擦过的玻璃棒所带的电荷，可用“”表示。 负电荷：指被毛皮摩擦过的橡胶棒所带的电荷，可用“”表示。 电荷间的相互作用： 同种电荷互相排斥，异种电荷互相吸引。 (3)检验物体是否带电的方法： 利用带电体具有的性质来判断。 例1.如果一个带电体吸引一个轻小物体，能否判断这个轻小物体也带电？ 分析：不能。如果轻小物体与带电体带异种电荷，它们之间可以相互吸引；如果轻小物体不带电，由于带电体的性质，它们之间也可以相互吸引。 例2.如果
6、一个带电体排斥一个轻小物体，能否判断这个轻小物体也带电？ 分析：可以。因为若轻小物体不带电，它们之间只能相互吸引，不会发生排斥现象。 例3.如果两个物体互相排斥，你能作出什么判断？ 分析：根据电荷间的相互作用，可以判断带电体必带同种电荷。 例4.有A、B、C、D四个带电体，若A排斥B，A吸引C，C排斥D，已知D带正电。那么A、B、C物体各带什么电？ 分析：已知D带正电可由此分析其他几个物体的带电性质。因为D带正电，D又排斥C，根据电荷间的相互作用，C应带正电。C吸引A，则A与C带异种电荷，即A带负电。A又排斥B，所以B也应带负电。 用验电器来检验。 验电器是实验室里常用的一种检验物体是否带电的
7、仪器。它是由金属球、金属杆、金属箔等几部分组成的（展示实物）。它的原理是利用了电荷间的相互作用。当用带电体接触验电器的金属球时，就有一部分电荷转移到验电器的金属箔片上，这两片金属箔由于带同种电荷互相排斥而张开。 演示实验：用被丝绸摩擦过的玻璃棒接触验电器的金属球，观察验电器金属箔片张开的角度，思考此时金属箔片带什么电？用力多摩擦几下玻璃棒，再去接触验电器的金属球，观察验电器金属箔片张开的角度有什么变化？张开角度的变化反映了什么？ 换用毛皮摩擦过的橡胶棒，重做上面的实验。 教师总结：验电器金属箔片张开的角度不同，反映了带电体传给验电器的电荷的多少不同。 (4)电量电荷的多少叫电量。 电量的单位是
8、库仑，简称库，符号是C。库仑是一个比较大的单位。一根摩擦过的玻璃棒或橡胶棒上所带的电量，大约只有107库仑，一片带电的云上所带的电量，大约有几十库仑。 (5)正、负电荷的中和 演示实验：把用丝绸摩擦过的玻璃棒接触验电器的金属球，使金属箔片张开一定的角度；再用毛皮摩擦过的橡胶棒去接触验电器的金属球，观察金属箔片张角的变化。 这个现象说明：正、负电荷放在一起会互相抵消。如果实验中的玻璃棒和橡胶棒带的电量相等，验电器的金属箔片将不再张开，即正、负电荷完全抵消。放在一起的等量异种电荷完全抵消的现象，叫做正、负电荷的中和。 思考题：将一物体跟一带正电的验电器的金属球接触时，验电器的金属箔先合拢后张开。
9、试分析这个物体的带电情况。 3.小结 这节课我们通过大量的实验，研究讨论了用摩擦的方法使物体带电后的性质、带电的种类及电荷间的相互作用。知道了怎样判断检验一个物体是否带电和带电的种类。那么摩擦起电的实质到底是什么呢？物体带正电、负电的本质又是什么呢？这些我们将在下一节里进行研究讨论。 4.布置作业。 (l)书上本节后的练习l、2、3。 (2)思考题：梳子与头发摩擦后，怎样检验梳子是否带电？带什么电？ (3)想一想，除了课上讲到的，还有哪些检验物体是否带电的方法。 备注：本教案依据的教材为人民教育出版社九年义务教育初中物理第二册第四章第一节。 荐初二物理浮力教学案例 (5000字) 荐初二物理教
10、案 物态变化 荐初中物理教学案例 123 荐初中物理教学设计和反思 (3000字) 荐初中物理教学案例密度 (800字) organization system and working mode, the selection of a number of municipal strengthening group to build innovation and strengthen the organization of the basic level organizations advanced model.(seven) the manual work of the Communist Y
11、outh League Organization published and League branch of manual work, to promote the use of two manuals in the citys organizations at various levels. The county committee, directly under the group (work) is under the jurisdiction of grassroots League and group (total) using branch ratio shall not be
12、less than 70%.Three, to further strengthen the groups leadership and team building(a) to strengthen the leagues leadership at all levels of construction. Continue to do a good job of municipal Party Committee Organization Department on the strengthening of the Communist Youth League cadres managemen
13、t opinions implementation. To promote the group counties (autonomous counties, cities) Commission and city directly under the group (workers) appointed to carry out the Five team building activities. Improve the League Association Department working mechanism. Conscientiously fulfill the duties of C
14、O, combined with the city group directly under (the) Committee of the general election and the adjustment, actively jointly with the unit where the party organization department good group leadership selection with the work. Do a good job in municipal Party committee assistant committee leadership a
15、nd leading cadres of the annual assessment work, adhere to and improve the assistant secretary of the Communist Youth League talk system group To weave individual conversation and collective conversation, to strengthen the committees of all levels, the Standing Committee of the Standing Committee, t
16、he establishment of a sound system of central group learning, the system of investigation and study, the system of important issues and the reporting system.(two) to strengthen the work of education and training of cadres to conscientiously implement the Central Committee. On the implementation of g
17、rassroots cadres training project and opinions on carrying out the mission municipal CYL Cadres training project implementation opinions, full implementation of the project of the City Youth League cadres training education. Focus on the county grassroots cadres and workers focused on training, the
18、new school system vocational training League cadres, for the Municipal Organization Department jointly held the third session of the Communist Youth League system training cadres in party. Focusing on the construction of new socialist countryside, strengthening village cadres and rural construction
19、team group member of the young team, the county organizations at various levels throughout the year is expected to train 100 00 rural grassroots cadres, plans to train 1000 village secretary of the village Party branch.(three) actively promote grassroots cadres election work. Under the unified leade
20、rship of the party organization, to strengthen grassroots organizations direct work, standardize the election work rules and procedures, in the designated candidate, open competition to democratically elected branch secretary at the same time, actively and steadily the development of Township, stree
21、ts and other grassroots organizations in the direct election of the pilot work, on the basis of summarizing the experience and gradually expand the scope of the pilot, and gradually formed a set of measures and cadres election system.(four) to strengthen the cadres testing exercise. To study the dev
22、elopment of XX city from 2006 to 2008 cadres testing exercise planning. To select outstanding cadres to the central mission in Beijing, Shanghai, Guangzhou and other central organs and sending work in developed areas. With the Central Committee the implementation of the western region and ethnic min
23、orities cadres training plan . To carry out the eighth batch of municipal organs attachment cadre management, selection, training work. The outstanding cadres to start the National Development Bank XX branch testing exercise.(five) to strengthen the group construction. The main position to play the
24、role of Youth League cadre education and training as the city, in accordance with the requirements of post training, further curriculum scientifically and rationally, adopt arrangement menu course, basic theory includes group work, focus, hot and difficult issues, to enhance the content and practice
25、; to strengthen the construction of teaching staff, the integration of teachers, establish a quality teacher training team, establish and implement course evaluation system; take delivery of training to the countryside, on-site training, and increase the rural grassroots cadres training efforts.Four
26、, efforts to strengthen the work of young talent(a) to tenth XX young 54 medal in recognition of the publicity, and actively explore the XX youth service. 54 Medal of institutionalization, standardization and socialization mechanism. Give full play to the XX award in recognition of 54 youth medal As
27、sociation, Youth Award winner in the 54 chapter, investigation activities. Who won the Youth Service medal, dedication to the society to create conditions, build the stage. During the 54, named in recognition of the tenth XX young 54 medal. The association of XX editing of young talent , the exchang
28、e of information and communication platform for the XX of outstanding young talents.(two) the establishment of municipal Party committee of young talent information database. In accordance with the feasible, effective, classification management, implement step by step principle, the establishment of
29、 municipal Party committee of youth talent database; guiding organizations at various levels generally established the young talent database, construction of city, county (directly under the Communist Youth League), grassroots organizations three young talent information database the relevant inform
30、ation collection system, and gradually establish the citys young people, the Communist Youth League youth talent information network, provide information platform for young talent resource development.Five, take effective measures to strengthen the mission management(a) to strengthen the mission man
31、agement work. Strengthen the dues collection and management, continue to adhere to the dues collection regularly reporting system, the annual comprehensive award in recognition of the tour and the tour one vote veto system audit system. Do statistical work in the group. The group service award in re
32、cognition of the advanced units, standardization, promoting group management work institutionalized.(two) to strengthen the organization of research and information exchange efforts. Grassroots carry out research, efforts to form a number of theoretical results. Make full use of the network carrier,
33、 to explore the establishment of electronic group service system, promote the work of Communist Youth League information.Attachment 4:XX municipal Party Committee Propaganda Department of the Communist Youth League work pointsIn 2006, the Communist Youth League propaganda ideological work XX to Deng Xiaoping theory and the important thought of Three Represents as guidance, study and implement the partys sixteen