题目内容
如图所示,光滑矩形斜面ABCD的倾角为
,在其上放置一矩形金属线框
,
的边长
,
的边长
,线框的质量
,电阻
,线框通过细线绕过定滑轮与重物相连,细线与斜面平行且靠近。重物质量
,离地面的高度为
。斜面上
区域是有界匀强磁场,方向垂直于斜面向上,已知AB到
的距离为
,
到
的距离为
,
到CD的距离为
,取
。现让线框从静止开始运动(开始时刻
与AB边重合),发现线框匀速穿过匀强磁场区域,求:
(1)efgh区域内匀强磁场的磁感应强度B
(2)线框在通过磁场区域过程中产生的焦耳热Q
(3)通过计算分析画出线框从开始运动到ab边与CD边重合过程中线框的
图象![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241643334805936.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164326553245.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164327006240.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164327489216.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164327895250.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164328113216.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164328581266.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164329158259.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164329548254.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164329923273.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164330188263.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164330422249.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164330640224.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164331202267.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164330640224.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164331732229.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164331951264.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164331732229.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164332325262.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164332559292.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164332902216.png)
(1)efgh区域内匀强磁场的磁感应强度B
(2)线框在通过磁场区域过程中产生的焦耳热Q
(3)通过计算分析画出线框从开始运动到ab边与CD边重合过程中线框的
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164333246219.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241643334805936.jpg)
v=" 3" m/s Q="4" C
="0." 5 J
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164333495373.png)
试题分析:(1)设M下落高度
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241643338701005.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164334135650.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241643345401261.png)
线框刚进入磁场时的速度:v=" 3" m/s ②
(2)线框进入磁场的过程中产生的感应电流的平均值为I,磁通量的变化量为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164334930458.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164335414385.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164335695552.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164336100531.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164336288696.png)
由③④⑤式得:Q="4" C ⑥
(3)当线框在匀速穿过ef边界时:设速度为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164336709313.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241643371611004.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164337333639.png)
由⑦⑧式得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164336709313.png)
设线框完全进入磁场时速度为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164337754355.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241643379411575.png)
得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164338347563.png)
从线框开始进入磁场到完全进入磁场的过程中,下滑高度为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164338737351.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164338924378.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164333495373.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241643397351774.png)
得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824164333495373.png)
点评:安培力的计算是关键.本题中运用的是整体法求解加速度
![](http://thumb2018.1010pic.com/images/loading.gif)
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