互感系数的大小取决于两个线圈的几何形状,大小,相对位置,各自的匝数以及它们周围介质的 ,互感系数一般通过实验方法来测定。
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由于导体本身电流的变化而产生的电磁感应现象叫做自感现象。自感现象有时非常有害,例如具有大自感线圈的电路断开时,因电流变化很快,会产生很大的自感电动势,导致击穿线圈的绝缘保护,或在电闸断开的间隙产生强烈电弧,可能烧坏电闸开关,如周围空气中有大量可燃性尘粒或气体还可引起爆炸。这些都应设法避免。
A. 对
B. 错
互感的基本原理就是磁的耦合。无论在何处,只要存在两个电流回路,就会有互感。一个回路的电流产生一个磁场,而该磁场会影响第二个回路。两个回路相互作用,其相互作用的系数随距离的增加而增加。两个回路之间相互作用的系数称为它们的互感。两个电路之间的互感耦合相当于一个连接在电路A和电路B之间的微小变压器。无论何处,对于两个相邻电流回路的相互作用,可以看成是一个变压器的初级和次级,从而得到互感。
A. 对
B. 错
________ refer to the marketing communications element that involves company-sponsored activities and programs designed to create daily or special brand-related interactions with consumers.
A. Publicity campaigns
B. Trade promotions
C. Advertisements
D. Events and experiences
Which of the following elements of the marketing communications mix includes a variety of programs directed internally to employees of the company or externally to consumers, other firms, the government, and media to promote or protect a company's image or its individual product communications?
A. direct marketing
B. public relations and publicity
C. personal selling
D. advertising