题目内容
(11分)如图所示,在xOy直角坐标系中,第Ⅰ象限内分布着方向垂直纸面向里的匀强磁场,第Ⅱ象限内分布着方向沿y轴负方向的匀强电场.初速度为零、带电荷量为q、质量为m的粒子经过电压为U的电场加速后,从x轴上的A点垂直x轴进入磁场区域,经磁场偏转后过y轴上的P点且垂直y轴进入电场区域,在电场中偏转并击中x轴上的C点.已知OA=OC=d.求电场强度E和磁感应强度B的大小(粒子的重力不计).
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250008500244159.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/201408250008500244159.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000850040528.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000850055816.png)
试题分析:设带电粒子经电压为U的电场加速后速度为v, qU=
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000850071339.png)
带电粒子进入磁场后,洛伦兹力提供向心力,由牛顿第二定律:qBv=
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000850086537.png)
依题意可知:r=d ③ (1分)
联立①②③可解得:B=
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000850055816.png)
带电粒子在电场中偏转,做类平抛运动,设经时间t从P点到达C点,由d=vt ⑤ (2分)
d=
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000850071339.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000850164546.png)
联立①⑤⑥可解得:E=
![](http://thumb.1010pic.com/pic2/upload/papers/20140825/20140825000850040528.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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