题目内容
(17分)如图13所示,一个半径为r的半圆形线圈,以直径ab为轴匀速转动,转速为n,ab的左侧有垂直于纸面向里(与ab垂直)的匀强磁场,磁感应强度为B.M和N是两个集流环,负载电阻为R,线圈、电流表和连接导线的电阻不计,求:
(1)从图示位置起转过1/4转的时间内负载电阻R上产生的
热量;
(2)从图示位置起转过1/4转的时间内通过负载电阻R的电
荷量;
(3)电流表的示数.
(1)从图示位置起转过1/4转的时间内负载电阻R上产生的
热量;
(2)从图示位置起转过1/4转的时间内通过负载电阻R的电
荷量;
(3)电流表的示数.
(1)
(2)
(3)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141632319760.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141632241801.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141632272679.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141632319760.png)
线圈绕轴匀速转动时,在电路中产生如图所示的交变电流.此交变电动势的最大值为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241416323662625.jpg)
Em=BSω=B·
·2πn=π2Bnr2.
(1)在线圈从图示位置转过1/4转的时间内,电动势的有效值为
E=
=![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141632522820.png)
电阻R上产生的热量
Q=(
)2R·
=
.
(2)在线圈从图示位置转过1/4转的时间内,电动势的平均值为
=
.
通过R的电荷量q=
·Δt=
·Δt=
=
.
(3)设此交变电动势在一个周期内的有效值为E′,由有效值的定义得
·
=
T
解得E′=
.
故电流表的示数为
I=
=
.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241416323662625.jpg)
Em=BSω=B·
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141632382544.png)
(1)在线圈从图示位置转过1/4转的时间内,电动势的有效值为
E=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141632475551.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141632522820.png)
电阻R上产生的热量
Q=(
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141632600440.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141632662389.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141632241801.png)
(2)在线圈从图示位置转过1/4转的时间内,电动势的平均值为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141632818321.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141632896508.png)
通过R的电荷量q=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141632974268.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141633021450.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141633505494.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141632272679.png)
(3)设此交变电动势在一个周期内的有效值为E′,由有效值的定义得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141633598829.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141633723406.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141633786519.png)
解得E′=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141633864518.png)
故电流表的示数为
I=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141633786519.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824141632319760.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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