题目内容
(12分)图(甲)为小型旋转电枢式交流发电机的原理图,其矩形线圈在匀强磁场中绕垂直于磁场方向的固定轴OO′匀速转动,线圈的匝数n =100匝、电阻r =10W,线圈的两端经集流环与电阻R连接,电阻R =" 90" Ω,与R并联的交流电压表为理想电表。在t =0时刻,线圈平面与磁场方向平行,穿过每匝线圈的磁通量F随时间t按图15(乙)所示正弦规律变化。 求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/2014082500000667415788.png)
(1) 从1.57×10-2s到4.71×10-2s内通过电阻R上的电量q。
(2)电路中交流电压表的示数。
(3)线圈匀速转动一周的过程中,外力所做的功W外。
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/2014082500000667415788.png)
(1) 从1.57×10-2s到4.71×10-2s内通过电阻R上的电量q。
(2)电路中交流电压表的示数。
(3)线圈匀速转动一周的过程中,外力所做的功W外。
(1)
;(2)
;(3)12.56J
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000006690461.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000006706473.png)
试题分析:由法拉第电磁感应定律可知,平均电动势
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250000067211084.png)
平均电流
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000006737623.png)
流过R的电量
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000006752541.png)
联立上式得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250000067682006.png)
(2)线圈转动的角速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250000067841015.png)
感应电动势最大值
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000006799723.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000006815169.png)
由图可知
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000006830981.png)
回路中的电流的有效值
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000006846900.png)
电压表示数
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000006846474.png)
联立上式得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000006877634.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000006893804.png)
(3)线圈匀速转动一周的过程中,外力所做的功W外=Q总=I2(R+r)t=12.56J 2分
![](http://thumb2018.1010pic.com/images/loading.gif)
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