3695911
幼苗
共回答了13个问题采纳率:100% 举报
当
![](https://img.yulucn.com/upload/a/c7/ac731616936476dd33ff43432e64b114_thumb.jpg)
由
![](https://img.yulucn.com/upload/d/27/d274cea697b758f7ef0239a3fd236818_thumb.jpg)
变化到
![](https://img.yulucn.com/upload/6/b3/6b37719f9826e6551f213ae0c95cb1b7_thumb.jpg)
的过程中,
![](https://img.yulucn.com/upload/a/06/a06bef1e795248e439887d79e9ddb658_thumb.jpg)
逐渐增大, s 也逐渐增大;当
![](https://img.yulucn.com/upload/a/c7/ac731616936476dd33ff43432e64b114_thumb.jpg)
由
![](https://img.yulucn.com/upload/6/b3/6b37719f9826e6551f213ae0c95cb1b7_thumb.jpg)
变化到
![](https://img.yulucn.com/upload/a/1d/a1d1b824623a3a35320f76a8da7a3eab_thumb.jpg)
的过程中,
![](https://img.yulucn.com/upload/a/06/a06bef1e795248e439887d79e9ddb658_thumb.jpg)
逐渐减小至零, s 也逐渐减小至零.故粒子打在荧光屏上的范围 s 为0~0. 15 m。
设粒子在磁场中沿 OB 弧做匀速圆周运动的半径为 r ,由牛顿第二定律得
![](https://img.yulucn.com/upload/3/48/3480477c96276e0cf8aa985e576282a9_thumb.jpg)
0.20 m
如图所示,当圆的直径 OD 转动到与 x 轴的夹角为
![](https://img.yulucn.com/upload/a/c7/ac731616936476dd33ff43432e64b114_thumb.jpg)
时,粒子从圆形磁场中的 B 点射出,粒子在磁场中的偏角为
![](https://img.yulucn.com/upload/a/06/a06bef1e795248e439887d79e9ddb658_thumb.jpg)
,打在荧光屏上的点到 x 轴的距离为 s ,由几何知识得
联立解得
代入数据并化简得
![](https://img.yulucn.com/upload/5/96/596d81ace614a73ff09f26bf4bfce18e_thumb.jpg)
m
故
![](https://img.yulucn.com/upload/a/06/a06bef1e795248e439887d79e9ddb658_thumb.jpg)
最大时, s 最大。如图,当 D 点与出射点 B 重合时,
![](https://img.yulucn.com/upload/a/06/a06bef1e795248e439887d79e9ddb658_thumb.jpg)
最大。由几何知识
![](https://img.yulucn.com/upload/d/c0/dc0b0d561ebeee80a45cecb92bd41272_thumb.jpg)
,得
求得粒子打在荧光屏上最远点到 x 轴的距离为
![](https://img.yulucn.com/upload/3/3c/33c2ba024156c1f056dbb764da42412b_thumb.jpg)
,此时
当
![](https://img.yulucn.com/upload/a/c7/ac731616936476dd33ff43432e64b114_thumb.jpg)
由
![](https://img.yulucn.com/upload/d/27/d274cea697b758f7ef0239a3fd236818_thumb.jpg)
变化到
![](https://img.yulucn.com/upload/6/b3/6b37719f9826e6551f213ae0c95cb1b7_thumb.jpg)
的过程中,
![](https://img.yulucn.com/upload/a/06/a06bef1e795248e439887d79e9ddb658_thumb.jpg)
逐渐增大, s 也逐渐增大;当
![](https://img.yulucn.com/upload/a/c7/ac731616936476dd33ff43432e64b114_thumb.jpg)
由
![](https://img.yulucn.com/upload/6/b3/6b37719f9826e6551f213ae0c95cb1b7_thumb.jpg)
变化到
![](https://img.yulucn.com/upload/a/1d/a1d1b824623a3a35320f76a8da7a3eab_thumb.jpg)
的过程中,
![](https://img.yulucn.com/upload/a/06/a06bef1e795248e439887d79e9ddb658_thumb.jpg)
逐渐减小至零, s 也逐渐减小至零.故粒子打在荧光屏上的范围 s 为0~0. 15 m。
1年前
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