题目内容
DVD光盘由塑料保护层和信息记录层组成。如图所示,激光束以入射角θ从空气入射到厚度为 d折射率为n的塑料保护层后,聚焦到信息记录层的光斑宽度为a,才能有效获取信息。
①写出sinθ应当满足的关系式;
②在保证a不变的前提下,减小激光束照到塑料保护层的宽度l(l=a +2b),可采取哪些措施?(答出三条措施即可)
(1)![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241357050323479.jpg)
①写出sinθ应当满足的关系式;
②在保证a不变的前提下,减小激光束照到塑料保护层的宽度l(l=a +2b),可采取哪些措施?(答出三条措施即可)
(1)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/201408241357050323479.jpg)
①
②见解析
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135705094942.png)
①由折射定律得
(2分)
式中r为折射角,
(2分)
解得
(2分)
②在保证
不变的前提下,减小激光束照到塑料保护层的宽度
,即减小
,由
的求解过程得
,故在
和
不变时,减小
;或在
和
不变时,增大
;或在
和
不变时,减小
。(每条1分,答出其他的合理措施也给分)
本题考查的是光的折射定律,射入保护膜后根据几何知识和折射定律可得关系式,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135705141658.png)
式中r为折射角,
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135705188837.png)
解得
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135705094942.png)
②在保证
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135705344283.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135705422280.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135705484299.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135705562205.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135705624993.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135705671297.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135705718297.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135705765333.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135705671297.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135705765333.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135705718297.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135705718297.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135705765333.png)
![](http://thumb.1010pic.com/pic2/upload/papers/20140824/20140824135705671297.png)
本题考查的是光的折射定律,射入保护膜后根据几何知识和折射定律可得关系式,
![](http://thumb2018.1010pic.com/images/loading.gif)
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