题目内容
【物理—物理3-4】(1)如图为某一简谐横波在某时刻的波形图,已知该机械波传播的速度为2m/s,此时质点a振动方向沿y轴正方向。则质点a的振动周期是 s,从此时刻开始质点b第一次到达波谷需要的时间是 s。
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241553194763725.png)
(2)如图所示,△ABC为折射率n=
的等腰直角三棱镜的横截面,∠C=90°,一束激光a平行于AB边射入棱镜,经一次折射后到达BC边。试通过计算说明激光能否从BC边射出?![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241553197262069.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241553194763725.png)
(2)如图所示,△ABC为折射率n=
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155319632317.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241553197262069.png)
(1) 2 1 (2) 激光不会从BC边射出
试题分析:(1)从图中可知该波的波长为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155319929534.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155320163529.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155320319475.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155320553684.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155320693531.png)
(2)如图
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241553208494855.jpg)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155320865769.png)
由于
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155321161465.png)
所以激光在AC边发生折射的折射角为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155321364480.png)
根据几何关系有
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155321457607.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155321691510.png)
发生全发射的临界角C
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155321785613.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155321925491.png)
所以
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824155322003464.png)
点评:在研究机械波振动时,需要根据走坡法判断波的传播方向,波上所有点的起振方向是相同的,在研究光的折射时,需要先画出光路图,结合几何知识分析解题
![](http://thumb2018.1010pic.com/images/loading.gif)
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