题目内容
光纤通信是一种现代化的通讯手段,为了研究问题的方便,我们将光导纤维简化为一根长直的玻璃柱,如图所示,设此玻璃柱长为L,折射率为n,且光在玻璃的侧壁上不能漏出.已知光在真空中的传播速度为c,则光通过此段玻璃管所需的最长时间为
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242022230404429.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408242022230404429.png)
A.nL/c | B.n2L/c2 |
C.nL/c2 | D.n2L/c |
D
试题分析:由
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202224069494.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202225442377.png)
光在玻璃的内界面上恰好发生全反射,由
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202226253558.png)
光在玻璃中沿玻璃管方向传播的速度为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202227252772.png)
则光在玻璃中传播的时间为:
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202228157737.png)
故选:D
点评:光的全反射必须从光密介质进入光疏介质,同时入射角大于临界角.考查运动的分解及
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202226253558.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202224069494.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824202231323466.png)
![](http://thumb2018.1010pic.com/images/loading.gif)
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