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# 课题：交变电流的产生和变化规律 - PowerPoint PPT Presentation

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### 课题：交变电流的产生和变化规律

♣ 电路性能更丰富、可用电元件更多

♣ 便于远距离输送

1.方向变化规律： 中性面--------在线圈平面垂直于磁感线时，各边都不切割磁感线，线圈中没有感应电流，这样的位置叫中性面。

V Yourself!

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V Yourself!

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eab=Blvsinωt

2. Yourself!大小变化规律------电动势的瞬时值

cd边中的感应电动势跟ab边中的大小相同，而且两边又是串联的，所以线圈中总感应电动势为

eab=2Blvsinωt

E r Yourself!

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R

• 把线圈的电阻组成闭合电路，电路中就有感应电流，实验证明，在只含有电阻的电路中，适用于直流电路的欧姆定律也适用于交流电路。其等效电路图如右：

i=Imsinωt Im叫电流的最大值

u=Umsinωt Um叫电压的最大值

ω=2πf=2π/ T

B Yourself!

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Em

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i Yourself!

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N Yourself!匝线圈的连接方式实质上是串联。

(1)e=NBSωsinωt，Em＝NBSω

(2)根据欧姆定律Im＝Em/Rn＝BSω/R

☆问题1：矩形线圈的面积为S，匝数为N，匀强磁场的磁感应强度为B，绕

中轴以ω角速度匀速转动。

（１）从线圈转到中性面开始计时，感应电动势的瞬时值表达式。

（２）若每匝线圈的电阻为R，则线圈中的感应电流的最大值是多少？

☆问题2：若从线圈转到与磁感线平行时开始计时，交变电流的波形图又

是怎样的呢？

☆问题3：交变电流能转换成直流电吗？