题目内容
如图所示,在第一象限有一匀强电场,场强大小为E,方向沿y轴负向;在x轴下方第四象限有一均强磁场,磁场方向垂直于纸面向里,磁感应强度为B.一质量为m、电荷量为q的带正电粒子以平行于x轴的速度从y轴上的P点处射入电场,在x轴上的Q点处进入磁场,粒子第二次经过x轴的M点,已知OP=
,
,不计重力.求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241259405142536.jpg)
小题1:M点与坐标原点O间的距离;
小题2:粒子从P点运动到M点所用的时间.
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940452185.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940483489.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241259405142536.jpg)
小题1:M点与坐标原点O间的距离;
小题2:粒子从P点运动到M点所用的时间.
小题1:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940530630.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940546277.gif)
小题2:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940592884.gif)
粒子的轨迹如图所示:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241259406086170.jpg)
(1)由图得:![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940639737.gif)
∴
2分
由粒子在电场中的运动可得:
1分
2分
求得:
∴
1分
粒子在磁场中的轨道半径
=
1分
M
=2
=
1分
∴M点与坐标原点O间的距离;OM=
+
1分
(2)带电粒子在磁场中做匀速圆周运动的周期
1分
由图可得:∠
=2
=60°
∴粒子从Q点经过磁场到达M点所用时间
1分
粒子从P点运动到M点所用的时间
2分
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241259406086170.jpg)
(1)由图得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940639737.gif)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940655299.gif)
由粒子在电场中的运动可得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940670459.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940686538.gif)
求得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940686606.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940717577.gif)
∴
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940733776.gif)
粒子在磁场中的轨道半径
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940748480.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940530630.gif)
M
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940780216.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940795391.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940530630.gif)
∴M点与坐标原点O间的距离;OM=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940530630.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940546277.gif)
(2)带电粒子在磁场中做匀速圆周运动的周期
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940858531.gif)
由图可得:∠
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940873428.gif)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940873201.gif)
∴粒子从Q点经过磁场到达M点所用时间
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940904758.gif)
粒子从P点运动到M点所用的时间
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824125940592884.gif)
![](http://thumb2018.1010pic.com/images/loading.gif)
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