题目内容
一棱镜的截面为直角三角形ABC,∠A=30o,斜边AB=
cm。棱镜材料的折射率为n=
。在此截面所在的平面内,一条光线以45o的入射角从AC边的中点M射入棱镜(如图所示)求:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241400058363211.jpg)
(1)光从棱镜射到空气的临界角
(2)求光从入射到第一次射出棱镜在棱镜所需的时间
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140005742421.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140005789336.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241400058363211.jpg)
(1)光从棱镜射到空气的临界角
(2)求光从入射到第一次射出棱镜在棱镜所需的时间
(1)45°(2)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241400058521144.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241400058521144.png)
(1)由
得 (1分)
光从棱镜射向空气是临界角为45° (1分)
(2)光在玻璃中的速度为:
(2分)
由数学知识得:
(2分)
(2分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241400058521144.png)
(2分)
本题考查光的全反射定律。根据判断光射入棱镜中后发生全反射,根据光在介质中的速度为:
,结合几何知识算出光从入射到第一次射出棱镜在棱镜所需的时间
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140005898612.png)
光从棱镜射向空气是临界角为45° (1分)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241400059616437.png)
(2)光在玻璃中的速度为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140006039495.png)
由数学知识得:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140006117956.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140006195737.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241400058521144.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140006273169.png)
本题考查光的全反射定律。根据判断光射入棱镜中后发生全反射,根据光在介质中的速度为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824140006039495.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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