题目内容
如图(a)所示, 水平放置的平行金属板AB间的距离
,板长
,在金属板的左端竖直放置一带有小孔的挡板,小孔恰好位于AB板的正中间.距金属板右端
处竖直放置一足够大的荧光屏.现在AB板间加如图(b)所示的方波形电压,已知
.在挡板的左侧,有大量带正电的相同粒子以平行于金属板方向的速度持续射向挡板,粒子的质量
,电荷量
,速度大小均为
.带电粒子的重力不计.求:
(1)在t=0时刻进入的粒子射出电场时竖直方向的速度
(2)荧光屏上出现的光带长度
(3)若撤去挡板,同时将粒子的速度均变为
,则荧光屏上出现的光带又为多长?![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082415175648413521.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151755595530.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151755673522.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151755813541.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151755891708.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151756047741.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151756157671.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151756281778.png)
(1)在t=0时刻进入的粒子射出电场时竖直方向的速度
(2)荧光屏上出现的光带长度
(3)若撤去挡板,同时将粒子的速度均变为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151756406810.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/2014082415175648413521.png)
(1)1000m/s (2)
(3)0.15m
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151756562741.png)
试题分析:(1)从
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151756640347.png)
在电场中运动时间
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151756703812.png)
竖直方向先加速后减速,加速度大小
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241517568431092.png)
射出电场时竖直方向的速度
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151756952957.png)
(2)无论何时进入电场,粒子射出电场时的速度均相同。
偏转最大的粒子偏转量
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241517570151897.png)
反方向最大偏转量
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241517571241948.png)
形成光带的总长度
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151756562741.png)
(3)因粒子的速度均变为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151756406810.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151757373407.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241517574831204.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241517578411206.png)
形成的光带长度
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824151757919866.png)
点评:学生要知道因电压变化,粒子在极板间做的不是类平抛运动,竖直方向粒子是先加速再减速,水平方向做匀速直线运动,然后用匀变速直线运动的公式去解题。
![](http://thumb2018.1010pic.com/images/loading.gif)
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